FreeBSD/Linux Kernel Cross Reference
sys/fs/exec.c

     /*
      *  linux/fs/exec.c
      *
      *  Copyright (C) 1991, 1992  Linus Torvalds
      */
     
     /*
      * #!-checking implemented by tytso.
      */
    /*
     * Demand-loading implemented 01.12.91 - no need to read anything but
     * the header into memory. The inode of the executable is put into
     * "current->executable", and page faults do the actual loading. Clean.
     *
     * Once more I can proudly say that linux stood up to being changed: it
     * was less than 2 hours work to get demand-loading completely implemented.
     *
     * Demand loading changed July 1993 by Eric Youngdale.   Use mmap instead,
     * current->executable is only used by the procfs.  This allows a dispatch
     * table to check for several different types  of binary formats.  We keep
     * trying until we recognize the file or we run out of supported binary
     * formats. 
     */
    
    #include <linux/slab.h>
    #include <linux/file.h>
    #include <linux/fdtable.h>
    #include <linux/mm.h>
    #include <linux/stat.h>
    #include <linux/fcntl.h>
    #include <linux/swap.h>
    #include <linux/string.h>
    #include <linux/init.h>
    #include <linux/pagemap.h>
    #include <linux/perf_event.h>
    #include <linux/highmem.h>
    #include <linux/spinlock.h>
    #include <linux/key.h>
    #include <linux/personality.h>
    #include <linux/binfmts.h>
    #include <linux/utsname.h>
    #include <linux/pid_namespace.h>
    #include <linux/module.h>
    #include <linux/namei.h>
    #include <linux/mount.h>
    #include <linux/security.h>
    #include <linux/syscalls.h>
    #include <linux/tsacct_kern.h>
    #include <linux/cn_proc.h>
    #include <linux/audit.h>
    #include <linux/tracehook.h>
    #include <linux/kmod.h>
    #include <linux/fsnotify.h>
    #include <linux/fs_struct.h>
    #include <linux/pipe_fs_i.h>
    #include <linux/oom.h>
    #include <linux/compat.h>
    
    #include <asm/uaccess.h>
    #include <asm/mmu_context.h>
    #include <asm/tlb.h>
    
    #include <trace/events/task.h>
    #include "internal.h"
    #include "coredump.h"
    
    #include <trace/events/sched.h>
    
    int suid_dumpable = 0;
    
    static LIST_HEAD(formats);
    static DEFINE_RWLOCK(binfmt_lock);
    
    void __register_binfmt(struct linux_binfmt * fmt, int insert)
    {
            BUG_ON(!fmt);
            write_lock(&binfmt_lock);
            insert ? list_add(&fmt->lh, &formats) :
                     list_add_tail(&fmt->lh, &formats);
            write_unlock(&binfmt_lock);
    }
    
    EXPORT_SYMBOL(__register_binfmt);
    
    void unregister_binfmt(struct linux_binfmt * fmt)
    {
            write_lock(&binfmt_lock);
            list_del(&fmt->lh);
            write_unlock(&binfmt_lock);
    }
    
    EXPORT_SYMBOL(unregister_binfmt);
    
    static inline void put_binfmt(struct linux_binfmt * fmt)
    {
            module_put(fmt->module);
    }
    
    /*
    * Note that a shared library must be both readable and executable due to
    * security reasons.
    *
    * Also note that we take the address to load from from the file itself.
    */
   SYSCALL_DEFINE1(uselib, const char __user *, library)
   {
           struct file *file;
           struct filename *tmp = getname(library);
           int error = PTR_ERR(tmp);
           static const struct open_flags uselib_flags = {
                   .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
                   .acc_mode = MAY_READ | MAY_EXEC | MAY_OPEN,
                   .intent = LOOKUP_OPEN
           };
   
           if (IS_ERR(tmp))
                   goto out;
   
           file = do_filp_open(AT_FDCWD, tmp, &uselib_flags, LOOKUP_FOLLOW);
           putname(tmp);
           error = PTR_ERR(file);
           if (IS_ERR(file))
                   goto out;
   
           error = -EINVAL;
           if (!S_ISREG(file->f_path.dentry->d_inode->i_mode))
                   goto exit;
   
           error = -EACCES;
           if (file->f_path.mnt->mnt_flags & MNT_NOEXEC)
                   goto exit;
   
           fsnotify_open(file);
   
           error = -ENOEXEC;
           if(file->f_op) {
                   struct linux_binfmt * fmt;
   
                   read_lock(&binfmt_lock);
                   list_for_each_entry(fmt, &formats, lh) {
                           if (!fmt->load_shlib)
                                   continue;
                           if (!try_module_get(fmt->module))
                                   continue;
                           read_unlock(&binfmt_lock);
                           error = fmt->load_shlib(file);
                           read_lock(&binfmt_lock);
                           put_binfmt(fmt);
                           if (error != -ENOEXEC)
                                   break;
                   }
                   read_unlock(&binfmt_lock);
           }
   exit:
           fput(file);
   out:
           return error;
   }
   
   #ifdef CONFIG_MMU
   /*
    * The nascent bprm->mm is not visible until exec_mmap() but it can
    * use a lot of memory, account these pages in current->mm temporary
    * for oom_badness()->get_mm_rss(). Once exec succeeds or fails, we
    * change the counter back via acct_arg_size(0).
    */
   static void acct_arg_size(struct linux_binprm *bprm, unsigned long pages)
   {
           struct mm_struct *mm = current->mm;
           long diff = (long)(pages - bprm->vma_pages);
   
           if (!mm || !diff)
                   return;
   
           bprm->vma_pages = pages;
           add_mm_counter(mm, MM_ANONPAGES, diff);
   }
   
   static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
                   int write)
   {
           struct page *page;
           int ret;
   
   #ifdef CONFIG_STACK_GROWSUP
           if (write) {
                   ret = expand_downwards(bprm->vma, pos);
                   if (ret < 0)
                           return NULL;
           }
   #endif
           ret = get_user_pages(current, bprm->mm, pos,
                           1, write, 1, &page, NULL);
           if (ret <= 0)
                   return NULL;
   
           if (write) {
                   unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start;
                   struct rlimit *rlim;
   
                   acct_arg_size(bprm, size / PAGE_SIZE);
   
                   /*
                    * We've historically supported up to 32 pages (ARG_MAX)
                    * of argument strings even with small stacks
                    */
                   if (size <= ARG_MAX)
                           return page;
   
                   /*
                    * Limit to 1/4-th the stack size for the argv+env strings.
                    * This ensures that:
                    *  - the remaining binfmt code will not run out of stack space,
                    *  - the program will have a reasonable amount of stack left
                    *    to work from.
                    */
                   rlim = current->signal->rlim;
                   if (size > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) {
                           put_page(page);
                           return NULL;
                   }
           }
   
           return page;
   }
   
   static void put_arg_page(struct page *page)
   {
           put_page(page);
   }
   
   static void free_arg_page(struct linux_binprm *bprm, int i)
   {
   }
   
   static void free_arg_pages(struct linux_binprm *bprm)
   {
   }
   
   static void flush_arg_page(struct linux_binprm *bprm, unsigned long pos,
                   struct page *page)
   {
           flush_cache_page(bprm->vma, pos, page_to_pfn(page));
   }
   
   static int __bprm_mm_init(struct linux_binprm *bprm)
   {
           int err;
           struct vm_area_struct *vma = NULL;
           struct mm_struct *mm = bprm->mm;
   
           bprm->vma = vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
           if (!vma)
                   return -ENOMEM;
   
           down_write(&mm->mmap_sem);
           vma->vm_mm = mm;
   
           /*
            * Place the stack at the largest stack address the architecture
            * supports. Later, we'll move this to an appropriate place. We don't
            * use STACK_TOP because that can depend on attributes which aren't
            * configured yet.
            */
           BUILD_BUG_ON(VM_STACK_FLAGS & VM_STACK_INCOMPLETE_SETUP);
           vma->vm_end = STACK_TOP_MAX;
           vma->vm_start = vma->vm_end - PAGE_SIZE;
           vma->vm_flags = VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP;
           vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
           INIT_LIST_HEAD(&vma->anon_vma_chain);
   
           err = insert_vm_struct(mm, vma);
           if (err)
                   goto err;
   
           mm->stack_vm = mm->total_vm = 1;
           up_write(&mm->mmap_sem);
           bprm->p = vma->vm_end - sizeof(void *);
           return 0;
   err:
           up_write(&mm->mmap_sem);
           bprm->vma = NULL;
           kmem_cache_free(vm_area_cachep, vma);
           return err;
   }
   
   static bool valid_arg_len(struct linux_binprm *bprm, long len)
   {
           return len <= MAX_ARG_STRLEN;
   }
   
   #else
   
   static inline void acct_arg_size(struct linux_binprm *bprm, unsigned long pages)
   {
   }
   
   static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
                   int write)
   {
           struct page *page;
   
           page = bprm->page[pos / PAGE_SIZE];
           if (!page && write) {
                   page = alloc_page(GFP_HIGHUSER|__GFP_ZERO);
                   if (!page)
                           return NULL;
                   bprm->page[pos / PAGE_SIZE] = page;
           }
   
           return page;
   }
   
   static void put_arg_page(struct page *page)
   {
   }
   
   static void free_arg_page(struct linux_binprm *bprm, int i)
   {
           if (bprm->page[i]) {
                   __free_page(bprm->page[i]);
                   bprm->page[i] = NULL;
           }
   }
   
   static void free_arg_pages(struct linux_binprm *bprm)
   {
           int i;
   
           for (i = 0; i < MAX_ARG_PAGES; i++)
                   free_arg_page(bprm, i);
   }
   
   static void flush_arg_page(struct linux_binprm *bprm, unsigned long pos,
                   struct page *page)
   {
   }
   
   static int __bprm_mm_init(struct linux_binprm *bprm)
   {
           bprm->p = PAGE_SIZE * MAX_ARG_PAGES - sizeof(void *);
           return 0;
   }
   
   static bool valid_arg_len(struct linux_binprm *bprm, long len)
   {
           return len <= bprm->p;
   }
   
   #endif /* CONFIG_MMU */
   
   /*
    * Create a new mm_struct and populate it with a temporary stack
    * vm_area_struct.  We don't have enough context at this point to set the stack
    * flags, permissions, and offset, so we use temporary values.  We'll update
    * them later in setup_arg_pages().
    */
   int bprm_mm_init(struct linux_binprm *bprm)
   {
           int err;
           struct mm_struct *mm = NULL;
   
           bprm->mm = mm = mm_alloc();
           err = -ENOMEM;
           if (!mm)
                   goto err;
   
           err = init_new_context(current, mm);
           if (err)
                   goto err;
   
           err = __bprm_mm_init(bprm);
           if (err)
                   goto err;
   
           return 0;
   
   err:
           if (mm) {
                   bprm->mm = NULL;
                   mmdrop(mm);
           }
   
           return err;
   }
   
   struct user_arg_ptr {
   #ifdef CONFIG_COMPAT
           bool is_compat;
   #endif
           union {
                   const char __user *const __user *native;
   #ifdef CONFIG_COMPAT
                   const compat_uptr_t __user *compat;
   #endif
           } ptr;
   };
   
   static const char __user *get_user_arg_ptr(struct user_arg_ptr argv, int nr)
   {
           const char __user *native;
   
   #ifdef CONFIG_COMPAT
           if (unlikely(argv.is_compat)) {
                   compat_uptr_t compat;
   
                   if (get_user(compat, argv.ptr.compat + nr))
                           return ERR_PTR(-EFAULT);
   
                   return compat_ptr(compat);
           }
   #endif
   
           if (get_user(native, argv.ptr.native + nr))
                   return ERR_PTR(-EFAULT);
   
           return native;
   }
   
   /*
    * count() counts the number of strings in array ARGV.
    */
   static int count(struct user_arg_ptr argv, int max)
   {
           int i = 0;
   
           if (argv.ptr.native != NULL) {
                   for (;;) {
                           const char __user *p = get_user_arg_ptr(argv, i);
   
                           if (!p)
                                   break;
   
                           if (IS_ERR(p))
                                   return -EFAULT;
   
                           if (i >= max)
                                   return -E2BIG;
                           ++i;
   
                           if (fatal_signal_pending(current))
                                   return -ERESTARTNOHAND;
                           cond_resched();
                   }
           }
           return i;
   }
   
   /*
    * 'copy_strings()' copies argument/environment strings from the old
    * processes's memory to the new process's stack.  The call to get_user_pages()
    * ensures the destination page is created and not swapped out.
    */
   static int copy_strings(int argc, struct user_arg_ptr argv,
                           struct linux_binprm *bprm)
   {
           struct page *kmapped_page = NULL;
           char *kaddr = NULL;
           unsigned long kpos = 0;
           int ret;
   
           while (argc-- > 0) {
                   const char __user *str;
                   int len;
                   unsigned long pos;
   
                   ret = -EFAULT;
                   str = get_user_arg_ptr(argv, argc);
                   if (IS_ERR(str))
                           goto out;
   
                   len = strnlen_user(str, MAX_ARG_STRLEN);
                   if (!len)
                           goto out;
   
                   ret = -E2BIG;
                   if (!valid_arg_len(bprm, len))
                           goto out;
   
                   /* We're going to work our way backwords. */
                   pos = bprm->p;
                   str += len;
                   bprm->p -= len;
   
                   while (len > 0) {
                           int offset, bytes_to_copy;
   
                           if (fatal_signal_pending(current)) {
                                   ret = -ERESTARTNOHAND;
                                   goto out;
                           }
                           cond_resched();
   
                           offset = pos % PAGE_SIZE;
                           if (offset == 0)
                                   offset = PAGE_SIZE;
   
                           bytes_to_copy = offset;
                           if (bytes_to_copy > len)
                                   bytes_to_copy = len;
   
                           offset -= bytes_to_copy;
                           pos -= bytes_to_copy;
                           str -= bytes_to_copy;
                           len -= bytes_to_copy;
   
                           if (!kmapped_page || kpos != (pos & PAGE_MASK)) {
                                   struct page *page;
   
                                   page = get_arg_page(bprm, pos, 1);
                                   if (!page) {
                                           ret = -E2BIG;
                                           goto out;
                                   }
   
                                   if (kmapped_page) {
                                           flush_kernel_dcache_page(kmapped_page);
                                           kunmap(kmapped_page);
                                           put_arg_page(kmapped_page);
                                   }
                                   kmapped_page = page;
                                   kaddr = kmap(kmapped_page);
                                   kpos = pos & PAGE_MASK;
                                   flush_arg_page(bprm, kpos, kmapped_page);
                           }
                           if (copy_from_user(kaddr+offset, str, bytes_to_copy)) {
                                   ret = -EFAULT;
                                   goto out;
                           }
                   }
           }
           ret = 0;
   out:
           if (kmapped_page) {
                   flush_kernel_dcache_page(kmapped_page);
                   kunmap(kmapped_page);
                   put_arg_page(kmapped_page);
           }
           return ret;
   }
   
   /*
    * Like copy_strings, but get argv and its values from kernel memory.
    */
   int copy_strings_kernel(int argc, const char *const *__argv,
                           struct linux_binprm *bprm)
   {
           int r;
           mm_segment_t oldfs = get_fs();
           struct user_arg_ptr argv = {
                   .ptr.native = (const char __user *const  __user *)__argv,
           };
   
           set_fs(KERNEL_DS);
           r = copy_strings(argc, argv, bprm);
           set_fs(oldfs);
   
           return r;
   }
   EXPORT_SYMBOL(copy_strings_kernel);
   
   #ifdef CONFIG_MMU
   
   /*
    * During bprm_mm_init(), we create a temporary stack at STACK_TOP_MAX.  Once
    * the binfmt code determines where the new stack should reside, we shift it to
    * its final location.  The process proceeds as follows:
    *
    * 1) Use shift to calculate the new vma endpoints.
    * 2) Extend vma to cover both the old and new ranges.  This ensures the
    *    arguments passed to subsequent functions are consistent.
    * 3) Move vma's page tables to the new range.
    * 4) Free up any cleared pgd range.
    * 5) Shrink the vma to cover only the new range.
    */
   static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
   {
           struct mm_struct *mm = vma->vm_mm;
           unsigned long old_start = vma->vm_start;
           unsigned long old_end = vma->vm_end;
           unsigned long length = old_end - old_start;
           unsigned long new_start = old_start - shift;
           unsigned long new_end = old_end - shift;
           struct mmu_gather tlb;
   
           BUG_ON(new_start > new_end);
   
           /*
            * ensure there are no vmas between where we want to go
            * and where we are
            */
           if (vma != find_vma(mm, new_start))
                   return -EFAULT;
   
           /*
            * cover the whole range: [new_start, old_end)
            */
           if (vma_adjust(vma, new_start, old_end, vma->vm_pgoff, NULL))
                   return -ENOMEM;
   
           /*
            * move the page tables downwards, on failure we rely on
            * process cleanup to remove whatever mess we made.
            */
           if (length != move_page_tables(vma, old_start,
                                          vma, new_start, length, false))
                   return -ENOMEM;
   
           lru_add_drain();
           tlb_gather_mmu(&tlb, mm, 0);
           if (new_end > old_start) {
                   /*
                    * when the old and new regions overlap clear from new_end.
                    */
                   free_pgd_range(&tlb, new_end, old_end, new_end,
                           vma->vm_next ? vma->vm_next->vm_start : 0);
           } else {
                   /*
                    * otherwise, clean from old_start; this is done to not touch
                    * the address space in [new_end, old_start) some architectures
                    * have constraints on va-space that make this illegal (IA64) -
                    * for the others its just a little faster.
                    */
                   free_pgd_range(&tlb, old_start, old_end, new_end,
                           vma->vm_next ? vma->vm_next->vm_start : 0);
           }
           tlb_finish_mmu(&tlb, new_end, old_end);
   
           /*
            * Shrink the vma to just the new range.  Always succeeds.
            */
           vma_adjust(vma, new_start, new_end, vma->vm_pgoff, NULL);
   
           return 0;
   }
   
   /*
    * Finalizes the stack vm_area_struct. The flags and permissions are updated,
    * the stack is optionally relocated, and some extra space is added.
    */
   int setup_arg_pages(struct linux_binprm *bprm,
                       unsigned long stack_top,
                       int executable_stack)
   {
           unsigned long ret;
           unsigned long stack_shift;
           struct mm_struct *mm = current->mm;
           struct vm_area_struct *vma = bprm->vma;
           struct vm_area_struct *prev = NULL;
           unsigned long vm_flags;
           unsigned long stack_base;
           unsigned long stack_size;
           unsigned long stack_expand;
           unsigned long rlim_stack;
   
   #ifdef CONFIG_STACK_GROWSUP
           /* Limit stack size to 1GB */
           stack_base = rlimit_max(RLIMIT_STACK);
           if (stack_base > (1 << 30))
                   stack_base = 1 << 30;
   
           /* Make sure we didn't let the argument array grow too large. */
           if (vma->vm_end - vma->vm_start > stack_base)
                   return -ENOMEM;
   
           stack_base = PAGE_ALIGN(stack_top - stack_base);
   
           stack_shift = vma->vm_start - stack_base;
           mm->arg_start = bprm->p - stack_shift;
           bprm->p = vma->vm_end - stack_shift;
   #else
           stack_top = arch_align_stack(stack_top);
           stack_top = PAGE_ALIGN(stack_top);
   
           if (unlikely(stack_top < mmap_min_addr) ||
               unlikely(vma->vm_end - vma->vm_start >= stack_top - mmap_min_addr))
                   return -ENOMEM;
   
           stack_shift = vma->vm_end - stack_top;
   
           bprm->p -= stack_shift;
           mm->arg_start = bprm->p;
   #endif
   
           if (bprm->loader)
                   bprm->loader -= stack_shift;
           bprm->exec -= stack_shift;
   
           down_write(&mm->mmap_sem);
           vm_flags = VM_STACK_FLAGS;
   
           /*
            * Adjust stack execute permissions; explicitly enable for
            * EXSTACK_ENABLE_X, disable for EXSTACK_DISABLE_X and leave alone
            * (arch default) otherwise.
            */
           if (unlikely(executable_stack == EXSTACK_ENABLE_X))
                   vm_flags |= VM_EXEC;
           else if (executable_stack == EXSTACK_DISABLE_X)
                   vm_flags &= ~VM_EXEC;
           vm_flags |= mm->def_flags;
           vm_flags |= VM_STACK_INCOMPLETE_SETUP;
   
           ret = mprotect_fixup(vma, &prev, vma->vm_start, vma->vm_end,
                           vm_flags);
           if (ret)
                   goto out_unlock;
           BUG_ON(prev != vma);
   
           /* Move stack pages down in memory. */
           if (stack_shift) {
                   ret = shift_arg_pages(vma, stack_shift);
                   if (ret)
                           goto out_unlock;
           }
   
           /* mprotect_fixup is overkill to remove the temporary stack flags */
           vma->vm_flags &= ~VM_STACK_INCOMPLETE_SETUP;
   
           stack_expand = 131072UL; /* randomly 32*4k (or 2*64k) pages */
           stack_size = vma->vm_end - vma->vm_start;
           /*
            * Align this down to a page boundary as expand_stack
            * will align it up.
            */
           rlim_stack = rlimit(RLIMIT_STACK) & PAGE_MASK;
   #ifdef CONFIG_STACK_GROWSUP
           if (stack_size + stack_expand > rlim_stack)
                   stack_base = vma->vm_start + rlim_stack;
           else
                   stack_base = vma->vm_end + stack_expand;
   #else
           if (stack_size + stack_expand > rlim_stack)
                   stack_base = vma->vm_end - rlim_stack;
           else
                   stack_base = vma->vm_start - stack_expand;
   #endif
           current->mm->start_stack = bprm->p;
           ret = expand_stack(vma, stack_base);
           if (ret)
                   ret = -EFAULT;
   
   out_unlock:
           up_write(&mm->mmap_sem);
           return ret;
   }
   EXPORT_SYMBOL(setup_arg_pages);
   
   #endif /* CONFIG_MMU */
   
   struct file *open_exec(const char *name)
   {
           struct file *file;
           int err;
           struct filename tmp = { .name = name };
           static const struct open_flags open_exec_flags = {
                   .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
                   .acc_mode = MAY_EXEC | MAY_OPEN,
                   .intent = LOOKUP_OPEN
           };
   
           file = do_filp_open(AT_FDCWD, &tmp, &open_exec_flags, LOOKUP_FOLLOW);
           if (IS_ERR(file))
                   goto out;
   
           err = -EACCES;
           if (!S_ISREG(file->f_path.dentry->d_inode->i_mode))
                   goto exit;
   
           if (file->f_path.mnt->mnt_flags & MNT_NOEXEC)
                   goto exit;
   
           fsnotify_open(file);
   
           err = deny_write_access(file);
           if (err)
                   goto exit;
   
   out:
           return file;
   
   exit:
           fput(file);
           return ERR_PTR(err);
   }
   EXPORT_SYMBOL(open_exec);
   
   int kernel_read(struct file *file, loff_t offset,
                   char *addr, unsigned long count)
   {
           mm_segment_t old_fs;
           loff_t pos = offset;
           int result;
   
           old_fs = get_fs();
           set_fs(get_ds());
           /* The cast to a user pointer is valid due to the set_fs() */
           result = vfs_read(file, (void __user *)addr, count, &pos);
           set_fs(old_fs);
           return result;
   }
   
   EXPORT_SYMBOL(kernel_read);
   
   static int exec_mmap(struct mm_struct *mm)
   {
           struct task_struct *tsk;
           struct mm_struct * old_mm, *active_mm;
   
           /* Notify parent that we're no longer interested in the old VM */
           tsk = current;
           old_mm = current->mm;
           mm_release(tsk, old_mm);
   
           if (old_mm) {
                   sync_mm_rss(old_mm);
                   /*
                    * Make sure that if there is a core dump in progress
                    * for the old mm, we get out and die instead of going
                    * through with the exec.  We must hold mmap_sem around
                    * checking core_state and changing tsk->mm.
                    */
                   down_read(&old_mm->mmap_sem);
                   if (unlikely(old_mm->core_state)) {
                           up_read(&old_mm->mmap_sem);
                           return -EINTR;
                   }
           }
           task_lock(tsk);
           active_mm = tsk->active_mm;
           tsk->mm = mm;
           tsk->active_mm = mm;
           activate_mm(active_mm, mm);
           task_unlock(tsk);
           arch_pick_mmap_layout(mm);
           if (old_mm) {
                   up_read(&old_mm->mmap_sem);
                   BUG_ON(active_mm != old_mm);
                   setmax_mm_hiwater_rss(&tsk->signal->maxrss, old_mm);
                   mm_update_next_owner(old_mm);
                   mmput(old_mm);
                   return 0;
           }
           mmdrop(active_mm);
           return 0;
   }
   
   /*
    * This function makes sure the current process has its own signal table,
    * so that flush_signal_handlers can later reset the handlers without
    * disturbing other processes.  (Other processes might share the signal
    * table via the CLONE_SIGHAND option to clone().)
    */
   static int de_thread(struct task_struct *tsk)
   {
           struct signal_struct *sig = tsk->signal;
           struct sighand_struct *oldsighand = tsk->sighand;
           spinlock_t *lock = &oldsighand->siglock;
   
           if (thread_group_empty(tsk))
                   goto no_thread_group;
   
           /*
            * Kill all other threads in the thread group.
            */
           spin_lock_irq(lock);
           if (signal_group_exit(sig)) {
                   /*
                    * Another group action in progress, just
                    * return so that the signal is processed.
                    */
                   spin_unlock_irq(lock);
                   return -EAGAIN;
           }
   
           sig->group_exit_task = tsk;
           sig->notify_count = zap_other_threads(tsk);
           if (!thread_group_leader(tsk))
                   sig->notify_count--;
   
           while (sig->notify_count) {
                   __set_current_state(TASK_KILLABLE);
                   spin_unlock_irq(lock);
                   schedule();
                   if (unlikely(__fatal_signal_pending(tsk)))
                           goto killed;
                   spin_lock_irq(lock);
           }
           spin_unlock_irq(lock);
   
           /*
            * At this point all other threads have exited, all we have to
            * do is to wait for the thread group leader to become inactive,
            * and to assume its PID:
            */
           if (!thread_group_leader(tsk)) {
                   struct task_struct *leader = tsk->group_leader;
   
                   sig->notify_count = -1; /* for exit_notify() */
                   for (;;) {
                           write_lock_irq(&tasklist_lock);
                           if (likely(leader->exit_state))
                                   break;
                           __set_current_state(TASK_KILLABLE);
                           write_unlock_irq(&tasklist_lock);
                           schedule();
                           if (unlikely(__fatal_signal_pending(tsk)))
                                   goto killed;
                   }
   
                   /*
                    * The only record we have of the real-time age of a
                    * process, regardless of execs it's done, is start_time.
                    * All the past CPU time is accumulated in signal_struct
                    * from sister threads now dead.  But in this non-leader
                    * exec, nothing survives from the original leader thread,
                    * whose birth marks the true age of this process now.
                    * When we take on its identity by switching to its PID, we
                    * also take its birthdate (always earlier than our own).
                    */
                   tsk->start_time = leader->start_time;
   
                   BUG_ON(!same_thread_group(leader, tsk));
                   BUG_ON(has_group_leader_pid(tsk));
                   /*
                    * An exec() starts a new thread group with the
                    * TGID of the previous thread group. Rehash the
                    * two threads with a switched PID, and release
                    * the former thread group leader:
                    */
   
                   /* Become a process group leader with the old leader's pid.
                    * The old leader becomes a thread of the this thread group.
                    * Note: The old leader also uses this pid until release_task
                    *       is called.  Odd but simple and correct.
                    */
                   detach_pid(tsk, PIDTYPE_PID);
                   tsk->pid = leader->pid;
                   attach_pid(tsk, PIDTYPE_PID,  task_pid(leader));
                   transfer_pid(leader, tsk, PIDTYPE_PGID);
                   transfer_pid(leader, tsk, PIDTYPE_SID);
   
                   list_replace_rcu(&leader->tasks, &tsk->tasks);
                   list_replace_init(&leader->sibling, &tsk->sibling);
   
                   tsk->group_leader = tsk;
                   leader->group_leader = tsk;
   
                   tsk->exit_signal = SIGCHLD;
                   leader->exit_signal = -1;
   
                   BUG_ON(leader->exit_state != EXIT_ZOMBIE);
                   leader->exit_state = EXIT_DEAD;
   
                   /*
                    * We are going to release_task()->ptrace_unlink() silently,
                    * the tracer can sleep in do_wait(). EXIT_DEAD guarantees
                    * the tracer wont't block again waiting for this thread.
                    */
                   if (unlikely(leader->ptrace))
                           __wake_up_parent(leader, leader->parent);
                   write_unlock_irq(&tasklist_lock);
   
                   release_task(leader);
           }
   
           sig->group_exit_task = NULL;
           sig->notify_count = 0;
   
   no_thread_group:
           /* we have changed execution domain */
           tsk->exit_signal = SIGCHLD;
   
           exit_itimers(sig);
           flush_itimer_signals();
   
           if (atomic_read(&oldsighand->count) != 1) {
                   struct sighand_struct *newsighand;
                   /*
                    * This ->sighand is shared with the CLONE_SIGHAND
                    * but not CLONE_THREAD task, switch to the new one.
                    */
                   newsighand = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
                   if (!newsighand)
                           return -ENOMEM;
   
                   atomic_set(&newsighand->count, 1);
                   memcpy(newsighand->action, oldsighand->action,
                          sizeof(newsighand->action));
   
                   write_lock_irq(&tasklist_lock);
                   spin_lock(&oldsighand->siglock);
                   rcu_assign_pointer(tsk->sighand, newsighand);
                   spin_unlock(&oldsighand->siglock);
                   write_unlock_irq(&tasklist_lock);
   
                   __cleanup_sighand(oldsighand);
           }
   
          BUG_ON(!thread_group_leader(tsk));
          return 0;
  
  killed:
          /* protects against exit_notify() and __exit_signal() */
          read_lock(&tasklist_lock);
          sig->group_exit_task = NULL;
          sig->notify_count = 0;
          read_unlock(&tasklist_lock);
          return -EAGAIN;
  }
  
  char *get_task_comm(char *buf, struct task_struct *tsk)
  {
          /* buf must be at least sizeof(tsk->comm) in size */
          task_lock(tsk);
          strncpy(buf, tsk->comm, sizeof(tsk->comm));
          task_unlock(tsk);
          return buf;
  }
  EXPORT_SYMBOL_GPL(get_task_comm);
  
  /*
   * These functions flushes out all traces of the currently running executable
   * so that a new one can be started
   */
  
  void set_task_comm(struct task_struct *tsk, char *buf)
  {
          task_lock(tsk);
  
          trace_task_rename(tsk, buf);
  
          /*
           * Threads may access current->comm without holding
           * the task lock, so write the string carefully.
           * Readers without a lock may see incomplete new
           * names but are safe from non-terminating string reads.
           */
          memset(tsk->comm, 0, TASK_COMM_LEN);
          wmb();
          strlcpy(tsk->comm, buf, sizeof(tsk->comm));
          task_unlock(tsk);
          perf_event_comm(tsk);
  }
  
  static void filename_to_taskname(char *tcomm, const char *fn, unsigned int len)
  {
          int i, ch;
  
          /* Copies the binary name from after last slash */
          for (i = 0; (ch = *(fn++)) != '\0';) {
                  if (ch == '/')
                          i = 0; /* overwrite what we wrote */
                  else
                          if (i < len - 1)
                                  tcomm[i++] = ch;
          }
          tcomm[i] = '\0';
  }
  
  int flush_old_exec(struct linux_binprm * bprm)
  {
          int retval;
  
          /*
           * Make sure we have a private signal table and that
           * we are unassociated from the previous thread group.
           */
          retval = de_thread(current);
          if (retval)
                  goto out;
  
          set_mm_exe_file(bprm->mm, bprm->file);
  
          filename_to_taskname(bprm->tcomm, bprm->filename, sizeof(bprm->tcomm));
          /*
           * Release all of the old mmap stuff
           */
          acct_arg_size(bprm, 0);
          retval = exec_mmap(bprm->mm);
          if (retval)
                  goto out;
  
          bprm->mm = NULL;                /* We're using it now */
  
          set_fs(USER_DS);
          current->flags &=
                  ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD | PF_NOFREEZE);
          flush_thread();
          current->personality &= ~bprm->per_clear;
  
          return 0;
  
  out:
          return retval;
  }
  EXPORT_SYMBOL(flush_old_exec);
  
  void would_dump(struct linux_binprm *bprm, struct file *file)
  {
          if (inode_permission(file->f_path.dentry->d_inode, MAY_READ) < 0)
                  bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
  }
  EXPORT_SYMBOL(would_dump);
  
  void setup_new_exec(struct linux_binprm * bprm)
  {
          arch_pick_mmap_layout(current->mm);
  
          /* This is the point of no return */
          current->sas_ss_sp = current->sas_ss_size = 0;
  
          if (uid_eq(current_euid(), current_uid()) && gid_eq(current_egid(), current_gid()))
                  set_dumpable(current->mm, SUID_DUMPABLE_ENABLED);
          else
                  set_dumpable(current->mm, suid_dumpable);
  
          set_task_comm(current, bprm->tcomm);
  
          /* Set the new mm task size. We have to do that late because it may
           * depend on TIF_32BIT which is only updated in flush_thread() on
           * some architectures like powerpc
           */
          current->mm->task_size = TASK_SIZE;
  
          /* install the new credentials */
          if (!uid_eq(bprm->cred->uid, current_euid()) ||
              !gid_eq(bprm->cred->gid, current_egid())) {
                  current->pdeath_signal = 0;
          } else {
                  would_dump(bprm, bprm->file);
                  if (bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP)
                          set_dumpable(current->mm, suid_dumpable);
          }
  
          /*
           * Flush performance counters when crossing a
           * security domain:
           */
          if (!get_dumpable(current->mm))
                  perf_event_exit_task(current);
  
          /* An exec changes our domain. We are no longer part of the thread
             group */
  
          current->self_exec_id++;
                          
          flush_signal_handlers(current, 0);
          do_close_on_exec(current->files);
  }
  EXPORT_SYMBOL(setup_new_exec);
  
  /*
   * Prepare credentials and lock ->cred_guard_mutex.
   * install_exec_creds() commits the new creds and drops the lock.
   * Or, if exec fails before, free_bprm() should release ->cred and
   * and unlock.
   */
  int prepare_bprm_creds(struct linux_binprm *bprm)
  {
          if (mutex_lock_interruptible(&current->signal->cred_guard_mutex))
                  return -ERESTARTNOINTR;
  
          bprm->cred = prepare_exec_creds();
          if (likely(bprm->cred))
                  return 0;
  
          mutex_unlock(&current->signal->cred_guard_mutex);
          return -ENOMEM;
  }
  
  void free_bprm(struct linux_binprm *bprm)
  {
          free_arg_pages(bprm);
          if (bprm->cred) {
                  mutex_unlock(&current->signal->cred_guard_mutex);
                  abort_creds(bprm->cred);
          }
          /* If a binfmt changed the interp, free it. */
          if (bprm->interp != bprm->filename)
                  kfree(bprm->interp);
          kfree(bprm);
  }
  
  int bprm_change_interp(char *interp, struct linux_binprm *bprm)
  {
          /* If a binfmt changed the interp, free it first. */
          if (bprm->interp != bprm->filename)
                  kfree(bprm->interp);
          bprm->interp = kstrdup(interp, GFP_KERNEL);
          if (!bprm->interp)
                  return -ENOMEM;
          return 0;
  }
  EXPORT_SYMBOL(bprm_change_interp);
  
  /*
   * install the new credentials for this executable
   */
  void install_exec_creds(struct linux_binprm *bprm)
  {
          security_bprm_committing_creds(bprm);
  
          commit_creds(bprm->cred);
          bprm->cred = NULL;
          /*
           * cred_guard_mutex must be held at least to this point to prevent
           * ptrace_attach() from altering our determination of the task's
           * credentials; any time after this it may be unlocked.
           */
          security_bprm_committed_creds(bprm);
          mutex_unlock(&current->signal->cred_guard_mutex);
  }
  EXPORT_SYMBOL(install_exec_creds);
  
  /*
   * determine how safe it is to execute the proposed program
   * - the caller must hold ->cred_guard_mutex to protect against
   *   PTRACE_ATTACH
   */
  static int check_unsafe_exec(struct linux_binprm *bprm)
  {
          struct task_struct *p = current, *t;
          unsigned n_fs;
          int res = 0;
  
          if (p->ptrace) {
                  if (p->ptrace & PT_PTRACE_CAP)
                          bprm->unsafe |= LSM_UNSAFE_PTRACE_CAP;
                  else
                          bprm->unsafe |= LSM_UNSAFE_PTRACE;
          }
  
          /*
           * This isn't strictly necessary, but it makes it harder for LSMs to
           * mess up.
           */
          if (current->no_new_privs)
                  bprm->unsafe |= LSM_UNSAFE_NO_NEW_PRIVS;
  
          n_fs = 1;
          spin_lock(&p->fs->lock);
          rcu_read_lock();
          for (t = next_thread(p); t != p; t = next_thread(t)) {
                  if (t->fs == p->fs)
                          n_fs++;
          }
          rcu_read_unlock();
  
          if (p->fs->users > n_fs) {
                  bprm->unsafe |= LSM_UNSAFE_SHARE;
          } else {
                  res = -EAGAIN;
                  if (!p->fs->in_exec) {
                          p->fs->in_exec = 1;
                          res = 1;
                  }
          }
          spin_unlock(&p->fs->lock);
  
          return res;
  }
  
  /* 
   * Fill the binprm structure from the inode. 
   * Check permissions, then read the first 128 (BINPRM_BUF_SIZE) bytes
   *
   * This may be called multiple times for binary chains (scripts for example).
   */
  int prepare_binprm(struct linux_binprm *bprm)
  {
          umode_t mode;
          struct inode * inode = bprm->file->f_path.dentry->d_inode;
          int retval;
  
          mode = inode->i_mode;
          if (bprm->file->f_op == NULL)
                  return -EACCES;
  
          /* clear any previous set[ug]id data from a previous binary */
          bprm->cred->euid = current_euid();
          bprm->cred->egid = current_egid();
  
          if (!(bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) &&
              !current->no_new_privs &&
              kuid_has_mapping(bprm->cred->user_ns, inode->i_uid) &&
              kgid_has_mapping(bprm->cred->user_ns, inode->i_gid)) {
                  /* Set-uid? */
                  if (mode & S_ISUID) {
                          bprm->per_clear |= PER_CLEAR_ON_SETID;
                          bprm->cred->euid = inode->i_uid;
                  }
  
                  /* Set-gid? */
                  /*
                   * If setgid is set but no group execute bit then this
                   * is a candidate for mandatory locking, not a setgid
                   * executable.
                   */
                  if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
                          bprm->per_clear |= PER_CLEAR_ON_SETID;
                          bprm->cred->egid = inode->i_gid;
                  }
          }
  
          /* fill in binprm security blob */
          retval = security_bprm_set_creds(bprm);
          if (retval)
                  return retval;
          bprm->cred_prepared = 1;
  
          memset(bprm->buf, 0, BINPRM_BUF_SIZE);
          return kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
  }
  
  EXPORT_SYMBOL(prepare_binprm);
  
  /*
   * Arguments are '\0' separated strings found at the location bprm->p
   * points to; chop off the first by relocating brpm->p to right after
   * the first '\0' encountered.
   */
  int remove_arg_zero(struct linux_binprm *bprm)
  {
          int ret = 0;
          unsigned long offset;
          char *kaddr;
          struct page *page;
  
          if (!bprm->argc)
                  return 0;
  
          do {
                  offset = bprm->p & ~PAGE_MASK;
                  page = get_arg_page(bprm, bprm->p, 0);
                  if (!page) {
                          ret = -EFAULT;
                          goto out;
                  }
                  kaddr = kmap_atomic(page);
  
                  for (; offset < PAGE_SIZE && kaddr[offset];
                                  offset++, bprm->p++)
                          ;
  
                  kunmap_atomic(kaddr);
                  put_arg_page(page);
  
                  if (offset == PAGE_SIZE)
                          free_arg_page(bprm, (bprm->p >> PAGE_SHIFT) - 1);
          } while (offset == PAGE_SIZE);
  
          bprm->p++;
          bprm->argc--;
          ret = 0;
  
  out:
          return ret;
  }
  EXPORT_SYMBOL(remove_arg_zero);
  
  /*
   * cycle the list of binary formats handler, until one recognizes the image
   */
  int search_binary_handler(struct linux_binprm *bprm)
  {
          unsigned int depth = bprm->recursion_depth;
          int try,retval;
          struct linux_binfmt *fmt;
          pid_t old_pid, old_vpid;
  
          /* This allows 4 levels of binfmt rewrites before failing hard. */
          if (depth > 5)
                  return -ELOOP;
  
          retval = security_bprm_check(bprm);
          if (retval)
                  return retval;
  
          retval = audit_bprm(bprm);
          if (retval)
                  return retval;
  
          /* Need to fetch pid before load_binary changes it */
          old_pid = current->pid;
          rcu_read_lock();
          old_vpid = task_pid_nr_ns(current, task_active_pid_ns(current->parent));
          rcu_read_unlock();
  
          retval = -ENOENT;
          for (try=0; try<2; try++) {
                  read_lock(&binfmt_lock);
                  list_for_each_entry(fmt, &formats, lh) {
                          int (*fn)(struct linux_binprm *) = fmt->load_binary;
                          if (!fn)
                                  continue;
                          if (!try_module_get(fmt->module))
                                  continue;
                          read_unlock(&binfmt_lock);
                          bprm->recursion_depth = depth + 1;
                          retval = fn(bprm);
                          bprm->recursion_depth = depth;
                          if (retval >= 0) {
                                  if (depth == 0) {
                                          trace_sched_process_exec(current, old_pid, bprm);
                                          ptrace_event(PTRACE_EVENT_EXEC, old_vpid);
                                  }
                                  put_binfmt(fmt);
                                  allow_write_access(bprm->file);
                                  if (bprm->file)
                                          fput(bprm->file);
                                  bprm->file = NULL;
                                  current->did_exec = 1;
                                  proc_exec_connector(current);
                                  return retval;
                          }
                          read_lock(&binfmt_lock);
                          put_binfmt(fmt);
                          if (retval != -ENOEXEC || bprm->mm == NULL)
                                  break;
                          if (!bprm->file) {
                                  read_unlock(&binfmt_lock);
                                  return retval;
                          }
                  }
                  read_unlock(&binfmt_lock);
  #ifdef CONFIG_MODULES
                  if (retval != -ENOEXEC || bprm->mm == NULL) {
                          break;
                  } else {
  #define printable(c) (((c)=='\t') || ((c)=='\n') || (0x20<=(c) && (c)<=0x7e))
                          if (printable(bprm->buf[0]) &&
                              printable(bprm->buf[1]) &&
                              printable(bprm->buf[2]) &&
                              printable(bprm->buf[3]))
                                  break; /* -ENOEXEC */
                          if (try)
                                  break; /* -ENOEXEC */
                          request_module("binfmt-%04x", *(unsigned short *)(&bprm->buf[2]));
                  }
  #else
                  break;
  #endif
          }
          return retval;
  }
  
  EXPORT_SYMBOL(search_binary_handler);
  
  /*
   * sys_execve() executes a new program.
   */
  static int do_execve_common(const char *filename,
                                  struct user_arg_ptr argv,
                                  struct user_arg_ptr envp)
  {
          struct linux_binprm *bprm;
          struct file *file;
          struct files_struct *displaced;
          bool clear_in_exec;
          int retval;
          const struct cred *cred = current_cred();
  
          /*
           * We move the actual failure in case of RLIMIT_NPROC excess from
           * set*uid() to execve() because too many poorly written programs
           * don't check setuid() return code.  Here we additionally recheck
           * whether NPROC limit is still exceeded.
           */
          if ((current->flags & PF_NPROC_EXCEEDED) &&
              atomic_read(&cred->user->processes) > rlimit(RLIMIT_NPROC)) {
                  retval = -EAGAIN;
                  goto out_ret;
          }
  
          /* We're below the limit (still or again), so we don't want to make
           * further execve() calls fail. */
          current->flags &= ~PF_NPROC_EXCEEDED;
  
          retval = unshare_files(&displaced);
          if (retval)
                  goto out_ret;
  
          retval = -ENOMEM;
          bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
          if (!bprm)
                  goto out_files;
  
          retval = prepare_bprm_creds(bprm);
          if (retval)
                  goto out_free;
  
          retval = check_unsafe_exec(bprm);
          if (retval < 0)
                  goto out_free;
          clear_in_exec = retval;
          current->in_execve = 1;
  
          file = open_exec(filename);
          retval = PTR_ERR(file);
          if (IS_ERR(file))
                  goto out_unmark;
  
          sched_exec();
  
          bprm->file = file;
          bprm->filename = filename;
          bprm->interp = filename;
  
          retval = bprm_mm_init(bprm);
          if (retval)
                  goto out_file;
  
          bprm->argc = count(argv, MAX_ARG_STRINGS);
          if ((retval = bprm->argc) < 0)
                  goto out;
  
          bprm->envc = count(envp, MAX_ARG_STRINGS);
          if ((retval = bprm->envc) < 0)
                  goto out;
  
          retval = prepare_binprm(bprm);
          if (retval < 0)
                  goto out;
  
          retval = copy_strings_kernel(1, &bprm->filename, bprm);
          if (retval < 0)
                  goto out;
  
          bprm->exec = bprm->p;
          retval = copy_strings(bprm->envc, envp, bprm);
          if (retval < 0)
                  goto out;
  
          retval = copy_strings(bprm->argc, argv, bprm);
          if (retval < 0)
                  goto out;
  
          retval = search_binary_handler(bprm);
          if (retval < 0)
                  goto out;
  
          /* execve succeeded */
          current->fs->in_exec = 0;
          current->in_execve = 0;
          acct_update_integrals(current);
          free_bprm(bprm);
          if (displaced)
                  put_files_struct(displaced);
          return retval;
  
  out:
          if (bprm->mm) {
                  acct_arg_size(bprm, 0);
                  mmput(bprm->mm);
          }
  
  out_file:
          if (bprm->file) {
                  allow_write_access(bprm->file);
                  fput(bprm->file);
          }
  
  out_unmark:
          if (clear_in_exec)
                  current->fs->in_exec = 0;
          current->in_execve = 0;
  
  out_free:
          free_bprm(bprm);
  
  out_files:
          if (displaced)
                  reset_files_struct(displaced);
  out_ret:
          return retval;
  }
  
  int do_execve(const char *filename,
          const char __user *const __user *__argv,
          const char __user *const __user *__envp)
  {
          struct user_arg_ptr argv = { .ptr.native = __argv };
          struct user_arg_ptr envp = { .ptr.native = __envp };
          return do_execve_common(filename, argv, envp);
  }
  
  #ifdef CONFIG_COMPAT
  static int compat_do_execve(const char *filename,
          const compat_uptr_t __user *__argv,
          const compat_uptr_t __user *__envp)
  {
          struct user_arg_ptr argv = {
                  .is_compat = true,
                  .ptr.compat = __argv,
          };
          struct user_arg_ptr envp = {
                  .is_compat = true,
                  .ptr.compat = __envp,
          };
          return do_execve_common(filename, argv, envp);
  }
  #endif
  
  void set_binfmt(struct linux_binfmt *new)
  {
          struct mm_struct *mm = current->mm;
  
          if (mm->binfmt)
                  module_put(mm->binfmt->module);
  
          mm->binfmt = new;
          if (new)
                  __module_get(new->module);
  }
  
  EXPORT_SYMBOL(set_binfmt);
  
  /*
   * set_dumpable converts traditional three-value dumpable to two flags and
   * stores them into mm->flags.  It modifies lower two bits of mm->flags, but
   * these bits are not changed atomically.  So get_dumpable can observe the
   * intermediate state.  To avoid doing unexpected behavior, get get_dumpable
   * return either old dumpable or new one by paying attention to the order of
   * modifying the bits.
   *
   * dumpable |   mm->flags (binary)
   * old  new | initial interim  final
   * ---------+-----------------------
   *  0    1  |   00      01      01
   *  0    2  |   00      10(*)   11
   *  1    0  |   01      00      00
   *  1    2  |   01      11      11
   *  2    0  |   11      10(*)   00
   *  2    1  |   11      11      01
   *
   * (*) get_dumpable regards interim value of 10 as 11.
   */
  void set_dumpable(struct mm_struct *mm, int value)
  {
          switch (value) {
          case SUID_DUMPABLE_DISABLED:
                  clear_bit(MMF_DUMPABLE, &mm->flags);
                  smp_wmb();
                  clear_bit(MMF_DUMP_SECURELY, &mm->flags);
                  break;
          case SUID_DUMPABLE_ENABLED:
                  set_bit(MMF_DUMPABLE, &mm->flags);
                  smp_wmb();
                  clear_bit(MMF_DUMP_SECURELY, &mm->flags);
                  break;
          case SUID_DUMPABLE_SAFE:
                  set_bit(MMF_DUMP_SECURELY, &mm->flags);
                  smp_wmb();
                  set_bit(MMF_DUMPABLE, &mm->flags);
                  break;
          }
  }
  
  int __get_dumpable(unsigned long mm_flags)
  {
          int ret;
  
          ret = mm_flags & MMF_DUMPABLE_MASK;
          return (ret > SUID_DUMPABLE_ENABLED) ? SUID_DUMPABLE_SAFE : ret;
  }
  
  int get_dumpable(struct mm_struct *mm)
  {
          return __get_dumpable(mm->flags);
  }
  
  SYSCALL_DEFINE3(execve,
                  const char __user *, filename,
                  const char __user *const __user *, argv,
                  const char __user *const __user *, envp)
  {
          struct filename *path = getname(filename);
          int error = PTR_ERR(path);
          if (!IS_ERR(path)) {
                  error = do_execve(path->name, argv, envp);
                  putname(path);
          }
          return error;
  }
  #ifdef CONFIG_COMPAT
  asmlinkage long compat_sys_execve(const char __user * filename,
          const compat_uptr_t __user * argv,
          const compat_uptr_t __user * envp)
  {
          struct filename *path = getname(filename);
          int error = PTR_ERR(path);
          if (!IS_ERR(path)) {
                  error = compat_do_execve(path->name, argv, envp);
                  putname(path);
          }
          return error;
  }
  #endif

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