FreeBSD/Linux Kernel Cross Reference
sys/kernel/capability.c

     /*
      * linux/kernel/capability.c
      *
      * Copyright (C) 1997  Andrew Main <zefram@fysh.org>
      *
      * Integrated into 2.1.97+,  Andrew G. Morgan <morgan@kernel.org>
      * 30 May 2002: Cleanup, Robert M. Love <rml@tech9.net>
      */
     
    #include <linux/audit.h>
    #include <linux/capability.h>
    #include <linux/mm.h>
    #include <linux/export.h>
    #include <linux/security.h>
    #include <linux/syscalls.h>
    #include <linux/pid_namespace.h>
    #include <linux/user_namespace.h>
    #include <asm/uaccess.h>
    
    /*
     * Leveraged for setting/resetting capabilities
     */
    
    const kernel_cap_t __cap_empty_set = CAP_EMPTY_SET;
    
    EXPORT_SYMBOL(__cap_empty_set);
    
    int file_caps_enabled = 1;
    
    static int __init file_caps_disable(char *str)
    {
            file_caps_enabled = 0;
            return 1;
    }
    __setup("no_file_caps", file_caps_disable);
    
    /*
     * More recent versions of libcap are available from:
     *
     *   http://www.kernel.org/pub/linux/libs/security/linux-privs/
     */
    
    static void warn_legacy_capability_use(void)
    {
            static int warned;
            if (!warned) {
                    char name[sizeof(current->comm)];
    
                    printk(KERN_INFO "warning: `%s' uses 32-bit capabilities"
                           " (legacy support in use)\n",
                           get_task_comm(name, current));
                    warned = 1;
            }
    }
    
    /*
     * Version 2 capabilities worked fine, but the linux/capability.h file
     * that accompanied their introduction encouraged their use without
     * the necessary user-space source code changes. As such, we have
     * created a version 3 with equivalent functionality to version 2, but
     * with a header change to protect legacy source code from using
     * version 2 when it wanted to use version 1. If your system has code
     * that trips the following warning, it is using version 2 specific
     * capabilities and may be doing so insecurely.
     *
     * The remedy is to either upgrade your version of libcap (to 2.10+,
     * if the application is linked against it), or recompile your
     * application with modern kernel headers and this warning will go
     * away.
     */
    
    static void warn_deprecated_v2(void)
    {
            static int warned;
    
            if (!warned) {
                    char name[sizeof(current->comm)];
    
                    printk(KERN_INFO "warning: `%s' uses deprecated v2"
                           " capabilities in a way that may be insecure.\n",
                           get_task_comm(name, current));
                    warned = 1;
            }
    }
    
    /*
     * Version check. Return the number of u32s in each capability flag
     * array, or a negative value on error.
     */
    static int cap_validate_magic(cap_user_header_t header, unsigned *tocopy)
    {
            __u32 version;
    
            if (get_user(version, &header->version))
                    return -EFAULT;
    
            switch (version) {
            case _LINUX_CAPABILITY_VERSION_1:
                    warn_legacy_capability_use();
                   *tocopy = _LINUX_CAPABILITY_U32S_1;
                   break;
           case _LINUX_CAPABILITY_VERSION_2:
                   warn_deprecated_v2();
                   /*
                    * fall through - v3 is otherwise equivalent to v2.
                    */
           case _LINUX_CAPABILITY_VERSION_3:
                   *tocopy = _LINUX_CAPABILITY_U32S_3;
                   break;
           default:
                   if (put_user((u32)_KERNEL_CAPABILITY_VERSION, &header->version))
                           return -EFAULT;
                   return -EINVAL;
           }
   
           return 0;
   }
   
   /*
    * The only thing that can change the capabilities of the current
    * process is the current process. As such, we can't be in this code
    * at the same time as we are in the process of setting capabilities
    * in this process. The net result is that we can limit our use of
    * locks to when we are reading the caps of another process.
    */
   static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
                                        kernel_cap_t *pIp, kernel_cap_t *pPp)
   {
           int ret;
   
           if (pid && (pid != task_pid_vnr(current))) {
                   struct task_struct *target;
   
                   rcu_read_lock();
   
                   target = find_task_by_vpid(pid);
                   if (!target)
                           ret = -ESRCH;
                   else
                           ret = security_capget(target, pEp, pIp, pPp);
   
                   rcu_read_unlock();
           } else
                   ret = security_capget(current, pEp, pIp, pPp);
   
           return ret;
   }
   
   /**
    * sys_capget - get the capabilities of a given process.
    * @header: pointer to struct that contains capability version and
    *      target pid data
    * @dataptr: pointer to struct that contains the effective, permitted,
    *      and inheritable capabilities that are returned
    *
    * Returns 0 on success and < 0 on error.
    */
   SYSCALL_DEFINE2(capget, cap_user_header_t, header, cap_user_data_t, dataptr)
   {
           int ret = 0;
           pid_t pid;
           unsigned tocopy;
           kernel_cap_t pE, pI, pP;
   
           ret = cap_validate_magic(header, &tocopy);
           if ((dataptr == NULL) || (ret != 0))
                   return ((dataptr == NULL) && (ret == -EINVAL)) ? 0 : ret;
   
           if (get_user(pid, &header->pid))
                   return -EFAULT;
   
           if (pid < 0)
                   return -EINVAL;
   
           ret = cap_get_target_pid(pid, &pE, &pI, &pP);
           if (!ret) {
                   struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
                   unsigned i;
   
                   for (i = 0; i < tocopy; i++) {
                           kdata[i].effective = pE.cap[i];
                           kdata[i].permitted = pP.cap[i];
                           kdata[i].inheritable = pI.cap[i];
                   }
   
                   /*
                    * Note, in the case, tocopy < _KERNEL_CAPABILITY_U32S,
                    * we silently drop the upper capabilities here. This
                    * has the effect of making older libcap
                    * implementations implicitly drop upper capability
                    * bits when they perform a: capget/modify/capset
                    * sequence.
                    *
                    * This behavior is considered fail-safe
                    * behavior. Upgrading the application to a newer
                    * version of libcap will enable access to the newer
                    * capabilities.
                    *
                    * An alternative would be to return an error here
                    * (-ERANGE), but that causes legacy applications to
                    * unexpectidly fail; the capget/modify/capset aborts
                    * before modification is attempted and the application
                    * fails.
                    */
                   if (copy_to_user(dataptr, kdata, tocopy
                                    * sizeof(struct __user_cap_data_struct))) {
                           return -EFAULT;
                   }
           }
   
           return ret;
   }
   
   /**
    * sys_capset - set capabilities for a process or (*) a group of processes
    * @header: pointer to struct that contains capability version and
    *      target pid data
    * @data: pointer to struct that contains the effective, permitted,
    *      and inheritable capabilities
    *
    * Set capabilities for the current process only.  The ability to any other
    * process(es) has been deprecated and removed.
    *
    * The restrictions on setting capabilities are specified as:
    *
    * I: any raised capabilities must be a subset of the old permitted
    * P: any raised capabilities must be a subset of the old permitted
    * E: must be set to a subset of new permitted
    *
    * Returns 0 on success and < 0 on error.
    */
   SYSCALL_DEFINE2(capset, cap_user_header_t, header, const cap_user_data_t, data)
   {
           struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
           unsigned i, tocopy, copybytes;
           kernel_cap_t inheritable, permitted, effective;
           struct cred *new;
           int ret;
           pid_t pid;
   
           ret = cap_validate_magic(header, &tocopy);
           if (ret != 0)
                   return ret;
   
           if (get_user(pid, &header->pid))
                   return -EFAULT;
   
           /* may only affect current now */
           if (pid != 0 && pid != task_pid_vnr(current))
                   return -EPERM;
   
           copybytes = tocopy * sizeof(struct __user_cap_data_struct);
           if (copybytes > sizeof(kdata))
                   return -EFAULT;
   
           if (copy_from_user(&kdata, data, copybytes))
                   return -EFAULT;
   
           for (i = 0; i < tocopy; i++) {
                   effective.cap[i] = kdata[i].effective;
                   permitted.cap[i] = kdata[i].permitted;
                   inheritable.cap[i] = kdata[i].inheritable;
           }
           while (i < _KERNEL_CAPABILITY_U32S) {
                   effective.cap[i] = 0;
                   permitted.cap[i] = 0;
                   inheritable.cap[i] = 0;
                   i++;
           }
   
           new = prepare_creds();
           if (!new)
                   return -ENOMEM;
   
           ret = security_capset(new, current_cred(),
                                 &effective, &inheritable, &permitted);
           if (ret < 0)
                   goto error;
   
           audit_log_capset(pid, new, current_cred());
   
           return commit_creds(new);
   
   error:
           abort_creds(new);
           return ret;
   }
   
   /**
    * has_ns_capability - Does a task have a capability in a specific user ns
    * @t: The task in question
    * @ns: target user namespace
    * @cap: The capability to be tested for
    *
    * Return true if the specified task has the given superior capability
    * currently in effect to the specified user namespace, false if not.
    *
    * Note that this does not set PF_SUPERPRIV on the task.
    */
   bool has_ns_capability(struct task_struct *t,
                          struct user_namespace *ns, int cap)
   {
           int ret;
   
           rcu_read_lock();
           ret = security_capable(__task_cred(t), ns, cap);
           rcu_read_unlock();
   
           return (ret == 0);
   }
   
   /**
    * has_capability - Does a task have a capability in init_user_ns
    * @t: The task in question
    * @cap: The capability to be tested for
    *
    * Return true if the specified task has the given superior capability
    * currently in effect to the initial user namespace, false if not.
    *
    * Note that this does not set PF_SUPERPRIV on the task.
    */
   bool has_capability(struct task_struct *t, int cap)
   {
           return has_ns_capability(t, &init_user_ns, cap);
   }
   
   /**
    * has_ns_capability_noaudit - Does a task have a capability (unaudited)
    * in a specific user ns.
    * @t: The task in question
    * @ns: target user namespace
    * @cap: The capability to be tested for
    *
    * Return true if the specified task has the given superior capability
    * currently in effect to the specified user namespace, false if not.
    * Do not write an audit message for the check.
    *
    * Note that this does not set PF_SUPERPRIV on the task.
    */
   bool has_ns_capability_noaudit(struct task_struct *t,
                                  struct user_namespace *ns, int cap)
   {
           int ret;
   
           rcu_read_lock();
           ret = security_capable_noaudit(__task_cred(t), ns, cap);
           rcu_read_unlock();
   
           return (ret == 0);
   }
   
   /**
    * has_capability_noaudit - Does a task have a capability (unaudited) in the
    * initial user ns
    * @t: The task in question
    * @cap: The capability to be tested for
    *
    * Return true if the specified task has the given superior capability
    * currently in effect to init_user_ns, false if not.  Don't write an
    * audit message for the check.
    *
    * Note that this does not set PF_SUPERPRIV on the task.
    */
   bool has_capability_noaudit(struct task_struct *t, int cap)
   {
           return has_ns_capability_noaudit(t, &init_user_ns, cap);
   }
   
   /**
    * ns_capable - Determine if the current task has a superior capability in effect
    * @ns:  The usernamespace we want the capability in
    * @cap: The capability to be tested for
    *
    * Return true if the current task has the given superior capability currently
    * available for use, false if not.
    *
    * This sets PF_SUPERPRIV on the task if the capability is available on the
    * assumption that it's about to be used.
    */
   bool ns_capable(struct user_namespace *ns, int cap)
   {
           if (unlikely(!cap_valid(cap))) {
                   printk(KERN_CRIT "capable() called with invalid cap=%u\n", cap);
                   BUG();
           }
   
           if (security_capable(current_cred(), ns, cap) == 0) {
                   current->flags |= PF_SUPERPRIV;
                   return true;
           }
           return false;
   }
   EXPORT_SYMBOL(ns_capable);
   
   /**
    * capable - Determine if the current task has a superior capability in effect
    * @cap: The capability to be tested for
    *
    * Return true if the current task has the given superior capability currently
    * available for use, false if not.
    *
    * This sets PF_SUPERPRIV on the task if the capability is available on the
    * assumption that it's about to be used.
    */
   bool capable(int cap)
   {
           return ns_capable(&init_user_ns, cap);
   }
   EXPORT_SYMBOL(capable);
   
   /**
    * nsown_capable - Check superior capability to one's own user_ns
    * @cap: The capability in question
    *
    * Return true if the current task has the given superior capability
    * targeted at its own user namespace.
    */
   bool nsown_capable(int cap)
   {
           return ns_capable(current_user_ns(), cap);
   }
   
   /**
    * inode_capable - Check superior capability over inode
    * @inode: The inode in question
    * @cap: The capability in question
    *
    * Return true if the current task has the given superior capability
    * targeted at it's own user namespace and that the given inode is owned
    * by the current user namespace or a child namespace.
    *
    * Currently we check to see if an inode is owned by the current
    * user namespace by seeing if the inode's owner maps into the
    * current user namespace.
    *
    */
   bool inode_capable(const struct inode *inode, int cap)
   {
           struct user_namespace *ns = current_user_ns();
   
           return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid);
   }

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