The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_exec.c

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    1 /*
    2  * Copyright (c) 1993, David Greenman
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  *
   14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   24  * SUCH DAMAGE.
   25  *
   26  * $FreeBSD$
   27  */
   28 
   29 #include <sys/param.h>
   30 #include <sys/systm.h>
   31 #include <sys/sysproto.h>
   32 #include <sys/kernel.h>
   33 #include <sys/mount.h>
   34 #include <sys/filedesc.h>
   35 #include <sys/fcntl.h>
   36 #include <sys/acct.h>
   37 #include <sys/exec.h>
   38 #include <sys/imgact.h>
   39 #include <sys/imgact_elf.h>
   40 #include <sys/wait.h>
   41 #include <sys/malloc.h>
   42 #include <sys/proc.h>
   43 #include <sys/signalvar.h>
   44 #include <sys/pioctl.h>
   45 #include <sys/namei.h>
   46 #include <sys/sysent.h>
   47 #include <sys/shm.h>
   48 #include <sys/sysctl.h>
   49 #include <sys/vnode.h>
   50 #include <sys/aio.h>
   51 
   52 #include <vm/vm.h>
   53 #include <vm/vm_param.h>
   54 #include <sys/lock.h>
   55 #include <vm/pmap.h>
   56 #include <vm/vm_page.h>
   57 #include <vm/vm_map.h>
   58 #include <vm/vm_kern.h>
   59 #include <vm/vm_extern.h>
   60 #include <vm/vm_object.h>
   61 #include <vm/vm_pager.h>
   62 
   63 #include <sys/user.h>
   64 #include <machine/reg.h>
   65 
   66 MALLOC_DEFINE(M_PARGS, "proc-args", "Process arguments");
   67 
   68 static register_t *exec_copyout_strings __P((struct image_params *));
   69 
   70 /* XXX This should be vm_size_t. */
   71 static u_long ps_strings = PS_STRINGS;
   72 SYSCTL_ULONG(_kern, KERN_PS_STRINGS, ps_strings, CTLFLAG_RD, &ps_strings, 0, "");
   73 
   74 /* XXX This should be vm_size_t. */
   75 static u_long usrstack = USRSTACK;
   76 SYSCTL_ULONG(_kern, KERN_USRSTACK, usrstack, CTLFLAG_RD, &usrstack, 0, "");
   77 
   78 u_long ps_arg_cache_limit = PAGE_SIZE / 16;
   79 SYSCTL_LONG(_kern, OID_AUTO, ps_arg_cache_limit, CTLFLAG_RW, 
   80     &ps_arg_cache_limit, 0, "");
   81 
   82 int ps_argsopen = 1;
   83 SYSCTL_INT(_kern, OID_AUTO, ps_argsopen, CTLFLAG_RW, &ps_argsopen, 0, "");
   84 
   85 /*
   86  * Each of the items is a pointer to a `const struct execsw', hence the
   87  * double pointer here.
   88  */
   89 static const struct execsw **execsw;
   90 
   91 #ifndef _SYS_SYSPROTO_H_
   92 struct execve_args {
   93         char    *fname; 
   94         char    **argv;
   95         char    **envv; 
   96 };
   97 #endif
   98 
   99 /*
  100  * execve() system call.
  101  */
  102 int
  103 execve(p, uap)
  104         struct proc *p;
  105         register struct execve_args *uap;
  106 {
  107         struct nameidata nd, *ndp;
  108         register_t *stack_base;
  109         int error, len, i;
  110         struct image_params image_params, *imgp;
  111         struct vattr attr;
  112         int (*img_first) __P((struct image_params *));
  113 
  114         imgp = &image_params;
  115 
  116         /*
  117          * Lock the process and set the P_INEXEC flag to indicate that
  118          * it should be left alone until we're done here.  This is
  119          * necessary to avoid race conditions - e.g. in ptrace() -
  120          * that might allow a local user to illicitly obtain elevated
  121          * privileges.
  122          */
  123         p->p_flag |= P_INEXEC;
  124 
  125         /*
  126          * Initialize part of the common data
  127          */
  128         imgp->proc = p;
  129         imgp->uap = uap;
  130         imgp->attr = &attr;
  131         imgp->argc = imgp->envc = 0;
  132         imgp->argv0 = NULL;
  133         imgp->entry_addr = 0;
  134         imgp->vmspace_destroyed = 0;
  135         imgp->interpreted = 0;
  136         imgp->interpreter_name[0] = '\0';
  137         imgp->auxargs = NULL;
  138         imgp->vp = NULL;
  139         imgp->firstpage = NULL;
  140         imgp->ps_strings = 0;
  141 
  142         /*
  143          * Allocate temporary demand zeroed space for argument and
  144          *      environment strings
  145          */
  146         imgp->stringbase = (char *)kmem_alloc_wait(exec_map, ARG_MAX + PAGE_SIZE);
  147         if (imgp->stringbase == NULL) {
  148                 error = ENOMEM;
  149                 goto exec_fail;
  150         }
  151         imgp->stringp = imgp->stringbase;
  152         imgp->stringspace = ARG_MAX;
  153         imgp->image_header = imgp->stringbase + ARG_MAX;
  154 
  155         /*
  156          * Translate the file name. namei() returns a vnode pointer
  157          *      in ni_vp amoung other things.
  158          */
  159         ndp = &nd;
  160         NDINIT(ndp, LOOKUP, LOCKLEAF | FOLLOW | SAVENAME,
  161             UIO_USERSPACE, uap->fname, p);
  162 
  163 interpret:
  164 
  165         error = namei(ndp);
  166         if (error) {
  167                 kmem_free_wakeup(exec_map, (vm_offset_t)imgp->stringbase,
  168                         ARG_MAX + PAGE_SIZE);
  169                 goto exec_fail;
  170         }
  171 
  172         imgp->vp = ndp->ni_vp;
  173         imgp->fname = uap->fname;
  174 
  175         /*
  176          * Check file permissions (also 'opens' file)
  177          */
  178         error = exec_check_permissions(imgp);
  179         if (error) {
  180                 VOP_UNLOCK(imgp->vp, 0, p);
  181                 goto exec_fail_dealloc;
  182         }
  183 
  184         error = exec_map_first_page(imgp);
  185         VOP_UNLOCK(imgp->vp, 0, p);
  186         if (error)
  187                 goto exec_fail_dealloc;
  188 
  189         /*
  190          *      If the current process has a special image activator it
  191          *      wants to try first, call it.   For example, emulating shell 
  192          *      scripts differently.
  193          */
  194         error = -1;
  195         if ((img_first = imgp->proc->p_sysent->sv_imgact_try) != NULL)
  196                 error = img_first(imgp);
  197 
  198         /*
  199          *      Loop through the list of image activators, calling each one.
  200          *      An activator returns -1 if there is no match, 0 on success,
  201          *      and an error otherwise.
  202          */
  203         for (i = 0; error == -1 && execsw[i]; ++i) {
  204                 if (execsw[i]->ex_imgact == NULL ||
  205                     execsw[i]->ex_imgact == img_first) {
  206                         continue;
  207                 }
  208                 error = (*execsw[i]->ex_imgact)(imgp);
  209         }
  210 
  211         if (error) {
  212                 if (error == -1)
  213                         error = ENOEXEC;
  214                 goto exec_fail_dealloc;
  215         }
  216 
  217         /*
  218          * Special interpreter operation, cleanup and loop up to try to
  219          * activate the interpreter.
  220          */
  221         if (imgp->interpreted) {
  222                 exec_unmap_first_page(imgp);
  223                 /* free name buffer and old vnode */
  224                 NDFREE(ndp, NDF_ONLY_PNBUF);
  225                 vrele(ndp->ni_vp);
  226                 /* set new name to that of the interpreter */
  227                 NDINIT(ndp, LOOKUP, LOCKLEAF | FOLLOW | SAVENAME,
  228                     UIO_SYSSPACE, imgp->interpreter_name, p);
  229                 goto interpret;
  230         }
  231 
  232         /*
  233          * Copy out strings (args and env) and initialize stack base
  234          */
  235         stack_base = exec_copyout_strings(imgp);
  236         p->p_vmspace->vm_minsaddr = (char *)stack_base;
  237 
  238         /*
  239          * If custom stack fixup routine present for this process
  240          * let it do the stack setup.
  241          * Else stuff argument count as first item on stack
  242          */
  243         if (p->p_sysent->sv_fixup)
  244                 (*p->p_sysent->sv_fixup)(&stack_base, imgp);
  245         else
  246                 suword(--stack_base, imgp->argc);
  247 
  248         /*
  249          * For security and other reasons, the file descriptor table cannot
  250          * be shared after an exec.
  251          */
  252         if (p->p_fd->fd_refcnt > 1) {
  253                 struct filedesc *tmp;
  254 
  255                 tmp = fdcopy(p);
  256                 fdfree(p);
  257                 p->p_fd = tmp;
  258         }
  259 
  260         /*
  261          * For security and other reasons, signal handlers cannot
  262          * be shared after an exec. The new proces gets a copy of the old
  263          * handlers. In execsigs(), the new process will have its signals
  264          * reset.
  265          */
  266         if (p->p_procsig->ps_refcnt > 1) {
  267                 struct procsig *newprocsig;
  268 
  269                 MALLOC(newprocsig, struct procsig *, sizeof(struct procsig),
  270                        M_SUBPROC, M_WAITOK);
  271                 bcopy(p->p_procsig, newprocsig, sizeof(*newprocsig));
  272                 p->p_procsig->ps_refcnt--;
  273                 p->p_procsig = newprocsig;
  274                 p->p_procsig->ps_refcnt = 1;
  275                 if (p->p_sigacts == &p->p_addr->u_sigacts)
  276                         panic("shared procsig but private sigacts?");
  277 
  278                 p->p_addr->u_sigacts = *p->p_sigacts;
  279                 p->p_sigacts = &p->p_addr->u_sigacts;
  280         }
  281 
  282         /* Stop profiling */
  283         stopprofclock(p);
  284 
  285         /* close files on exec */
  286         fdcloseexec(p);
  287 
  288         /* reset caught signals */
  289         execsigs(p);
  290 
  291         /* name this process - nameiexec(p, ndp) */
  292         len = min(ndp->ni_cnd.cn_namelen,MAXCOMLEN);
  293         bcopy(ndp->ni_cnd.cn_nameptr, p->p_comm, len);
  294         p->p_comm[len] = 0;
  295 
  296         /*
  297          * mark as execed, wakeup the process that vforked (if any) and tell
  298          * it that it now has its own resources back
  299          */
  300         p->p_flag |= P_EXEC;
  301         if (p->p_pptr && (p->p_flag & P_PPWAIT)) {
  302                 p->p_flag &= ~P_PPWAIT;
  303                 wakeup((caddr_t)p->p_pptr);
  304         }
  305 
  306         /*
  307          * Implement image setuid/setgid.
  308          *
  309          * Don't honor setuid/setgid if the filesystem prohibits it or if
  310          * the process is being traced.
  311          */
  312         if ((((attr.va_mode & VSUID) && p->p_ucred->cr_uid != attr.va_uid) ||
  313              ((attr.va_mode & VSGID) && p->p_ucred->cr_gid != attr.va_gid)) &&
  314             (imgp->vp->v_mount->mnt_flag & MNT_NOSUID) == 0 &&
  315             (p->p_flag & P_TRACED) == 0) {
  316                 /*
  317                  * Turn off syscall tracing for set-id programs, except for
  318                  * root.  Record any set-id flags first to make sure that
  319                  * we do not regain any tracing during a possible block.
  320                  */
  321                 setsugid(p);
  322                 if (p->p_tracep && suser(p)) {
  323                         struct vnode *vtmp;
  324 
  325                         if ((vtmp = p->p_tracep) != NULL) {
  326                                 p->p_tracep = NULL;
  327                                 p->p_traceflag = 0;
  328                                 vrele(vtmp);
  329                         }
  330                 }
  331                 /* Close any file descriptors 0..2 that reference procfs */
  332                 setugidsafety(p);
  333                 /* Make sure file descriptors 0..2 are in use. */
  334                 error = fdcheckstd(p);
  335                 if (error != 0)
  336                         goto exec_fail_dealloc;
  337                 /*
  338                  * Set the new credentials.
  339                  */
  340                 p->p_ucred = crcopy(p->p_ucred);
  341                 if (attr.va_mode & VSUID)
  342                         change_euid(p, attr.va_uid);
  343                 if (attr.va_mode & VSGID)
  344                         p->p_ucred->cr_gid = attr.va_gid;
  345         } else {
  346                 if (p->p_ucred->cr_uid == p->p_cred->p_ruid &&
  347                     p->p_ucred->cr_gid == p->p_cred->p_rgid)
  348                         p->p_flag &= ~P_SUGID;
  349         }
  350 
  351         /*
  352          * Implement correct POSIX saved-id behavior.
  353          */
  354         p->p_cred->p_svuid = p->p_ucred->cr_uid;
  355         p->p_cred->p_svgid = p->p_ucred->cr_gid;
  356 
  357         /*
  358          * Store the vp for use in procfs
  359          */
  360         if (p->p_textvp)                /* release old reference */
  361                 vrele(p->p_textvp);
  362         VREF(ndp->ni_vp);
  363         p->p_textvp = ndp->ni_vp;
  364 
  365         /*
  366          * Notify others that we exec'd, and clear the P_INEXEC flag
  367          * as we're now a bona fide freshly-execed process.
  368          */
  369         KNOTE(&p->p_klist, NOTE_EXEC);
  370         p->p_flag &= ~P_INEXEC;
  371 
  372         /*
  373          * If tracing the process, trap to debugger so breakpoints
  374          *      can be set before the program executes.
  375          */
  376         STOPEVENT(p, S_EXEC, 0);
  377 
  378         if (p->p_flag & P_TRACED)
  379                 psignal(p, SIGTRAP);
  380 
  381         /* clear "fork but no exec" flag, as we _are_ execing */
  382         p->p_acflag &= ~AFORK;
  383 
  384         /* Set values passed into the program in registers. */
  385         setregs(p, imgp->entry_addr, (u_long)(uintptr_t)stack_base,
  386             imgp->ps_strings);
  387 
  388         /* Free any previous argument cache */
  389         if (p->p_args && --p->p_args->ar_ref == 0)
  390                 FREE(p->p_args, M_PARGS);
  391         p->p_args = NULL;
  392 
  393         /* Cache arguments if they fit inside our allowance */
  394         i = imgp->endargs - imgp->stringbase;
  395         if (ps_arg_cache_limit >= i + sizeof(struct pargs)) {
  396                 MALLOC(p->p_args, struct pargs *, sizeof(struct pargs) + i, 
  397                     M_PARGS, M_WAITOK);
  398                 p->p_args->ar_ref = 1;
  399                 p->p_args->ar_length = i;
  400                 bcopy(imgp->stringbase, p->p_args->ar_args, i);
  401         }
  402 
  403 exec_fail_dealloc:
  404 
  405         /*
  406          * free various allocated resources
  407          */
  408         if (imgp->firstpage)
  409                 exec_unmap_first_page(imgp);
  410 
  411         if (imgp->stringbase != NULL)
  412                 kmem_free_wakeup(exec_map, (vm_offset_t)imgp->stringbase,
  413                         ARG_MAX + PAGE_SIZE);
  414 
  415         if (imgp->vp) {
  416                 NDFREE(ndp, NDF_ONLY_PNBUF);
  417                 vrele(imgp->vp);
  418         }
  419 
  420         if (error == 0)
  421                 return (0);
  422 
  423 exec_fail:
  424         /* we're done here, clear P_INEXEC */
  425         p->p_flag &= ~P_INEXEC;
  426         if (imgp->vmspace_destroyed) {
  427                 /* sorry, no more process anymore. exit gracefully */
  428                 exit1(p, W_EXITCODE(0, SIGABRT));
  429                 /* NOT REACHED */
  430                 return(0);
  431         } else {
  432                 return(error);
  433         }
  434 }
  435 
  436 int
  437 exec_map_first_page(imgp)
  438         struct image_params *imgp;
  439 {
  440         int s, rv, i;
  441         int initial_pagein;
  442         vm_page_t ma[VM_INITIAL_PAGEIN];
  443         vm_object_t object;
  444 
  445 
  446         if (imgp->firstpage) {
  447                 exec_unmap_first_page(imgp);
  448         }
  449 
  450         VOP_GETVOBJECT(imgp->vp, &object);
  451         s = splvm();
  452 
  453         ma[0] = vm_page_grab(object, 0, VM_ALLOC_NORMAL | VM_ALLOC_RETRY);
  454 
  455         if ((ma[0]->valid & VM_PAGE_BITS_ALL) != VM_PAGE_BITS_ALL) {
  456                 initial_pagein = VM_INITIAL_PAGEIN;
  457                 if (initial_pagein > object->size)
  458                         initial_pagein = object->size;
  459                 for (i = 1; i < initial_pagein; i++) {
  460                         if ((ma[i] = vm_page_lookup(object, i)) != NULL) {
  461                                 if ((ma[i]->flags & PG_BUSY) || ma[i]->busy)
  462                                         break;
  463                                 if (ma[i]->valid)
  464                                         break;
  465                                 vm_page_busy(ma[i]);
  466                         } else {
  467                                 ma[i] = vm_page_alloc(object, i, VM_ALLOC_NORMAL);
  468                                 if (ma[i] == NULL)
  469                                         break;
  470                         }
  471                 }
  472                 initial_pagein = i;
  473 
  474                 rv = vm_pager_get_pages(object, ma, initial_pagein, 0);
  475                 ma[0] = vm_page_lookup(object, 0);
  476 
  477                 if ((rv != VM_PAGER_OK) || (ma[0] == NULL) || (ma[0]->valid == 0)) {
  478                         if (ma[0]) {
  479                                 vm_page_protect(ma[0], VM_PROT_NONE);
  480                                 vm_page_free(ma[0]);
  481                         }
  482                         splx(s);
  483                         return EIO;
  484                 }
  485         }
  486 
  487         vm_page_wire(ma[0]);
  488         vm_page_wakeup(ma[0]);
  489         splx(s);
  490 
  491         pmap_kenter((vm_offset_t) imgp->image_header, VM_PAGE_TO_PHYS(ma[0]));
  492         imgp->firstpage = ma[0];
  493 
  494         return 0;
  495 }
  496 
  497 void
  498 exec_unmap_first_page(imgp)
  499         struct image_params *imgp;
  500 {
  501         if (imgp->firstpage) {
  502                 pmap_kremove((vm_offset_t) imgp->image_header);
  503                 vm_page_unwire(imgp->firstpage, 1);
  504                 imgp->firstpage = NULL;
  505         }
  506 }
  507 
  508 /*
  509  * Destroy old address space, and allocate a new stack
  510  *      The new stack is only SGROWSIZ large because it is grown
  511  *      automatically in trap.c.
  512  */
  513 int
  514 exec_new_vmspace(imgp)
  515         struct image_params *imgp;
  516 {
  517         int error;
  518         struct vmspace *vmspace = imgp->proc->p_vmspace;
  519         vm_offset_t stack_addr = USRSTACK - maxssiz;
  520         vm_map_t map = &vmspace->vm_map;
  521 
  522         imgp->vmspace_destroyed = 1;
  523 
  524         /*
  525          * Prevent a pending AIO from modifying the new address space.
  526          */
  527         aio_proc_rundown(imgp->proc);
  528 
  529         /*
  530          * Blow away entire process VM, if address space not shared,
  531          * otherwise, create a new VM space so that other threads are
  532          * not disrupted
  533          */
  534         if (vmspace->vm_refcnt == 1) {
  535                 if (vmspace->vm_shm)
  536                         shmexit(imgp->proc);
  537                 pmap_remove_pages(vmspace_pmap(vmspace), 0, VM_MAXUSER_ADDRESS);
  538                 vm_map_remove(map, 0, VM_MAXUSER_ADDRESS);
  539         } else {
  540                 vmspace_exec(imgp->proc);
  541                 vmspace = imgp->proc->p_vmspace;
  542                 map = &vmspace->vm_map;
  543         }
  544 
  545         /* Allocate a new stack */
  546         error = vm_map_stack(&vmspace->vm_map, stack_addr, (vm_size_t)maxssiz,
  547             VM_PROT_ALL, VM_PROT_ALL, 0);
  548         if (error)
  549                 return (error);
  550 
  551         /* vm_ssize and vm_maxsaddr are somewhat antiquated concepts in the
  552          * VM_STACK case, but they are still used to monitor the size of the
  553          * process stack so we can check the stack rlimit.
  554          */
  555         vmspace->vm_ssize = sgrowsiz >> PAGE_SHIFT;
  556         vmspace->vm_maxsaddr = (char *)USRSTACK - maxssiz;
  557 
  558         return(0);
  559 }
  560 
  561 /*
  562  * Copy out argument and environment strings from the old process
  563  *      address space into the temporary string buffer.
  564  */
  565 int
  566 exec_extract_strings(imgp)
  567         struct image_params *imgp;
  568 {
  569         char    **argv, **envv;
  570         char    *argp, *envp;
  571         int     error;
  572         size_t  length;
  573 
  574         /*
  575          * extract arguments first
  576          */
  577 
  578         argv = imgp->uap->argv;
  579 
  580         if (argv) {
  581                 argp = (caddr_t) (intptr_t) fuword(argv);
  582                 if (argp == (caddr_t) -1)
  583                         return (EFAULT);
  584                 if (argp)
  585                         argv++;
  586                 if (imgp->argv0)
  587                         argp = imgp->argv0;
  588                 if (argp) {
  589                         do {
  590                                 if (argp == (caddr_t) -1)
  591                                         return (EFAULT);
  592                                 if ((error = copyinstr(argp, imgp->stringp,
  593                                     imgp->stringspace, &length))) {
  594                                         if (error == ENAMETOOLONG)
  595                                                 return(E2BIG);
  596                                         return (error);
  597                                 }
  598                                 imgp->stringspace -= length;
  599                                 imgp->stringp += length;
  600                                 imgp->argc++;
  601                         } while ((argp = (caddr_t) (intptr_t) fuword(argv++)));
  602                 }
  603         }       
  604 
  605         imgp->endargs = imgp->stringp;
  606 
  607         /*
  608          * extract environment strings
  609          */
  610 
  611         envv = imgp->uap->envv;
  612 
  613         if (envv) {
  614                 while ((envp = (caddr_t) (intptr_t) fuword(envv++))) {
  615                         if (envp == (caddr_t) -1)
  616                                 return (EFAULT);
  617                         if ((error = copyinstr(envp, imgp->stringp,
  618                             imgp->stringspace, &length))) {
  619                                 if (error == ENAMETOOLONG)
  620                                         return(E2BIG);
  621                                 return (error);
  622                         }
  623                         imgp->stringspace -= length;
  624                         imgp->stringp += length;
  625                         imgp->envc++;
  626                 }
  627         }
  628 
  629         return (0);
  630 }
  631 
  632 /*
  633  * Copy strings out to the new process address space, constructing
  634  *      new arg and env vector tables. Return a pointer to the base
  635  *      so that it can be used as the initial stack pointer.
  636  */
  637 register_t *
  638 exec_copyout_strings(imgp)
  639         struct image_params *imgp;
  640 {
  641         int argc, envc;
  642         char **vectp;
  643         char *stringp, *destp;
  644         register_t *stack_base;
  645         struct ps_strings *arginfo;
  646         int szsigcode;
  647 
  648         /*
  649          * Calculate string base and vector table pointers.
  650          * Also deal with signal trampoline code for this exec type.
  651          */
  652         arginfo = (struct ps_strings *)PS_STRINGS;
  653         szsigcode = *(imgp->proc->p_sysent->sv_szsigcode);
  654         destp = (caddr_t)arginfo - szsigcode - SPARE_USRSPACE -
  655                 roundup((ARG_MAX - imgp->stringspace), sizeof(char *));
  656 
  657         /*
  658          * install sigcode
  659          */
  660         if (szsigcode)
  661                 copyout(imgp->proc->p_sysent->sv_sigcode,
  662                         ((caddr_t)arginfo - szsigcode), szsigcode);
  663 
  664         /*
  665          * If we have a valid auxargs ptr, prepare some room
  666          * on the stack.
  667          */
  668         if (imgp->auxargs)
  669         /*
  670          * The '+ 2' is for the null pointers at the end of each of the
  671          * arg and env vector sets, and 'AT_COUNT*2' is room for the
  672          * ELF Auxargs data.
  673          */
  674                 vectp = (char **)(destp - (imgp->argc + imgp->envc + 2 +
  675                                   AT_COUNT*2) * sizeof(char*));
  676         else 
  677         /*
  678          * The '+ 2' is for the null pointers at the end of each of the
  679          * arg and env vector sets
  680          */
  681                 vectp = (char **)
  682                         (destp - (imgp->argc + imgp->envc + 2) * sizeof(char*));
  683 
  684         /*
  685          * vectp also becomes our initial stack base
  686          */
  687         stack_base = (register_t *)vectp;
  688 
  689         stringp = imgp->stringbase;
  690         argc = imgp->argc;
  691         envc = imgp->envc;
  692 
  693         /*
  694          * Copy out strings - arguments and environment.
  695          */
  696         copyout(stringp, destp, ARG_MAX - imgp->stringspace);
  697 
  698         /*
  699          * Fill in "ps_strings" struct for ps, w, etc.
  700          */
  701         suword(&arginfo->ps_argvstr, (long)(intptr_t)vectp);
  702         suword(&arginfo->ps_nargvstr, argc);
  703 
  704         /*
  705          * Fill in argument portion of vector table.
  706          */
  707         for (; argc > 0; --argc) {
  708                 suword(vectp++, (long)(intptr_t)destp);
  709                 while (*stringp++ != 0)
  710                         destp++;
  711                 destp++;
  712         }
  713 
  714         /* a null vector table pointer seperates the argp's from the envp's */
  715         suword(vectp++, 0);
  716 
  717         suword(&arginfo->ps_envstr, (long)(intptr_t)vectp);
  718         suword(&arginfo->ps_nenvstr, envc);
  719 
  720         /*
  721          * Fill in environment portion of vector table.
  722          */
  723         for (; envc > 0; --envc) {
  724                 suword(vectp++, (long)(intptr_t)destp);
  725                 while (*stringp++ != 0)
  726                         destp++;
  727                 destp++;
  728         }
  729 
  730         /* end of vector table is a null pointer */
  731         suword(vectp, 0);
  732 
  733         return (stack_base);
  734 }
  735 
  736 /*
  737  * Check permissions of file to execute.
  738  *      Return 0 for success or error code on failure.
  739  */
  740 int
  741 exec_check_permissions(imgp)
  742         struct image_params *imgp;
  743 {
  744         struct proc *p = imgp->proc;
  745         struct vnode *vp = imgp->vp;
  746         struct vattr *attr = imgp->attr;
  747         int error;
  748 
  749         /* Get file attributes */
  750         error = VOP_GETATTR(vp, attr, p->p_ucred, p);
  751         if (error)
  752                 return (error);
  753 
  754         /*
  755          * 1) Check if file execution is disabled for the filesystem that this
  756          *      file resides on.
  757          * 2) Insure that at least one execute bit is on - otherwise root
  758          *      will always succeed, and we don't want to happen unless the
  759          *      file really is executable.
  760          * 3) Insure that the file is a regular file.
  761          */
  762         if ((vp->v_mount->mnt_flag & MNT_NOEXEC) ||
  763             ((attr->va_mode & 0111) == 0) ||
  764             (attr->va_type != VREG)) {
  765                 return (EACCES);
  766         }
  767 
  768         /*
  769          * Zero length files can't be exec'd
  770          */
  771         if (attr->va_size == 0)
  772                 return (ENOEXEC);
  773 
  774         /*
  775          *  Check for execute permission to file based on current credentials.
  776          */
  777         error = VOP_ACCESS(vp, VEXEC, p->p_ucred, p);
  778         if (error)
  779                 return (error);
  780 
  781         /*
  782          * Check number of open-for-writes on the file and deny execution
  783          * if there are any.
  784          */
  785         if (vp->v_writecount)
  786                 return (ETXTBSY);
  787 
  788         /*
  789          * Call filesystem specific open routine (which does nothing in the
  790          * general case).
  791          */
  792         error = VOP_OPEN(vp, FREAD, p->p_ucred, p);
  793         if (error)
  794                 return (error);
  795 
  796         return (0);
  797 }
  798 
  799 /*
  800  * Exec handler registration
  801  */
  802 int
  803 exec_register(execsw_arg)
  804         const struct execsw *execsw_arg;
  805 {
  806         const struct execsw **es, **xs, **newexecsw;
  807         int count = 2;  /* New slot and trailing NULL */
  808 
  809         if (execsw)
  810                 for (es = execsw; *es; es++)
  811                         count++;
  812         newexecsw = malloc(count * sizeof(*es), M_TEMP, M_WAITOK);
  813         if (newexecsw == NULL)
  814                 return ENOMEM;
  815         xs = newexecsw;
  816         if (execsw)
  817                 for (es = execsw; *es; es++)
  818                         *xs++ = *es;
  819         *xs++ = execsw_arg;
  820         *xs = NULL;
  821         if (execsw)
  822                 free(execsw, M_TEMP);
  823         execsw = newexecsw;
  824         return 0;
  825 }
  826 
  827 int
  828 exec_unregister(execsw_arg)
  829         const struct execsw *execsw_arg;
  830 {
  831         const struct execsw **es, **xs, **newexecsw;
  832         int count = 1;
  833 
  834         if (execsw == NULL)
  835                 panic("unregister with no handlers left?\n");
  836 
  837         for (es = execsw; *es; es++) {
  838                 if (*es == execsw_arg)
  839                         break;
  840         }
  841         if (*es == NULL)
  842                 return ENOENT;
  843         for (es = execsw; *es; es++)
  844                 if (*es != execsw_arg)
  845                         count++;
  846         newexecsw = malloc(count * sizeof(*es), M_TEMP, M_WAITOK);
  847         if (newexecsw == NULL)
  848                 return ENOMEM;
  849         xs = newexecsw;
  850         for (es = execsw; *es; es++)
  851                 if (*es != execsw_arg)
  852                         *xs++ = *es;
  853         *xs = NULL;
  854         if (execsw)
  855                 free(execsw, M_TEMP);
  856         execsw = newexecsw;
  857         return 0;
  858 }

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