sysdeps/posix/spawni.c

   1 /* Guts of POSIX spawn interface.  Generic POSIX.1 version.
   2    Copyright (C) 2000-2019 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <spawn.h>
  20 #include <assert.h>
  21 #include <fcntl.h>
  22 #include <paths.h>
  23 #include <string.h>
  24 #include <sys/resource.h>
  25 #include <sys/wait.h>
  26 #include <sys/param.h>
  27 #include <sys/mman.h>
  28 #include <not-cancel.h>
  29 #include <local-setxid.h>
  30 #include <shlib-compat.h>
  31 #include <nptl/pthreadP.h>
  32 #include <dl-sysdep.h>
  33 #include <libc-pointer-arith.h>
  34 #include <ldsodefs.h>
  35 #include "spawn_int.h"
  36
  37
  38 /* The Unix standard contains a long explanation of the way to signal
  39    an error after the fork() was successful.  Since no new wait status
  40    was wanted there is no way to signal an error using one of the
  41    available methods.  The committee chose to signal an error by a
  42    normal program exit with the exit code 127.  */
  43 #define SPAWN_ERROR     127
  44
  45 struct posix_spawn_args
  46 {
  47   sigset_t oldmask;
  48   const char *file;
  49   int (*exec) (const char *, char *const *, char *const *);
  50   const posix_spawn_file_actions_t *fa;
  51   const posix_spawnattr_t *restrict attr;
  52   char *const *argv;
  53   ptrdiff_t argc;
  54   char *const *envp;
  55   int xflags;
  56   int pipe[2];
  57 };
  58
  59 /* Older version requires that shell script without shebang definition
  60    to be called explicitly using /bin/sh (_PATH_BSHELL).  */
  61 static void
  62 maybe_script_execute (struct posix_spawn_args *args)
  63 {
  64   if (SHLIB_COMPAT (libc, GLIBC_2_2, GLIBC_2_15)
  65       && (args->xflags & SPAWN_XFLAGS_TRY_SHELL) && errno == ENOEXEC)
  66     {
  67       char *const *argv = args->argv;
  68       ptrdiff_t argc = args->argc;
  69
  70       /* Construct an argument list for the shell.  */
  71       char *new_argv[argc + 2];
  72       new_argv[0] = (char *) _PATH_BSHELL;
  73       new_argv[1] = (char *) args->file;
  74       if (argc > 1)
  75         memcpy (new_argv + 2, argv + 1, argc * sizeof(char *));
  76       else
  77         new_argv[2] = NULL;
  78
  79       /* Execute the shell.  */
  80       args->exec (new_argv[0], new_argv, args->envp);
  81     }
  82 }
  83
  84 /* Function used in the clone call to setup the signals mask, posix_spawn
  85    attributes, and file actions.  */
  86 static int
  87 __spawni_child (void *arguments)
  88 {
  89   struct posix_spawn_args *args = arguments;
  90   const posix_spawnattr_t *restrict attr = args->attr;
  91   const posix_spawn_file_actions_t *file_actions = args->fa;
  92   int ret;
  93
  94   __close (args->pipe[0]);
  95
  96   /* Set signal default action.  */
  97   if ((attr->__flags & POSIX_SPAWN_SETSIGDEF) != 0)
  98     {
  99       /* We have to iterate over all signals.  This could possibly be
 100          done better but it requires system specific solutions since
 101          the sigset_t data type can be very different on different
 102          architectures.  */
 103       int sig;
 104       struct sigaction sa;
 105
 106       memset (&sa, '\0', sizeof (sa));
 107       sa.sa_handler = SIG_DFL;
 108
 109       for (sig = 1; sig <= _NSIG; ++sig)
 110         if (__sigismember (&attr->__sd, sig) != 0
 111             && __sigaction (sig, &sa, NULL) != 0)
 112           goto fail;
 113     }
 114
 115 #ifdef _POSIX_PRIORITY_SCHEDULING
 116   /* Set the scheduling algorithm and parameters.  */
 117   if ((attr->__flags & (POSIX_SPAWN_SETSCHEDPARAM | POSIX_SPAWN_SETSCHEDULER))
 118       == POSIX_SPAWN_SETSCHEDPARAM)
 119     {
 120       if (__sched_setparam (0, &attr->__sp) == -1)
 121         goto fail;
 122     }
 123   else if ((attr->__flags & POSIX_SPAWN_SETSCHEDULER) != 0)
 124     {
 125       if (__sched_setscheduler (0, attr->__policy, &attr->__sp) == -1)
 126         goto fail;
 127     }
 128 #endif
 129
 130   /* Set the process session ID.  */
 131   if ((attr->__flags & POSIX_SPAWN_SETSID) != 0
 132       && __setsid () < 0)
 133     goto fail;
 134
 135   /* Set the process group ID.  */
 136   if ((attr->__flags & POSIX_SPAWN_SETPGROUP) != 0
 137       && __setpgid (0, attr->__pgrp) != 0)
 138     goto fail;
 139
 140   /* Set the effective user and group IDs.  */
 141   if ((attr->__flags & POSIX_SPAWN_RESETIDS) != 0
 142       && (local_seteuid (__getuid ()) != 0
 143           || local_setegid (__getgid ())) != 0)
 144     goto fail;
 145
 146   /* Execute the file actions.  */
 147   if (file_actions != NULL)
 148     {
 149       int cnt;
 150       struct rlimit64 fdlimit;
 151       bool have_fdlimit = false;
 152
 153       for (cnt = 0; cnt < file_actions->__used; ++cnt)
 154         {
 155           struct __spawn_action *action = &file_actions->__actions[cnt];
 156
 157           switch (action->tag)
 158             {
 159             case spawn_do_close:
 160               if (__close_nocancel (action->action.close_action.fd) != 0)
 161                 {
 162                   if (have_fdlimit == 0)
 163                     {
 164                       __getrlimit64 (RLIMIT_NOFILE, &fdlimit);
 165                       have_fdlimit = true;
 166                     }
 167
 168                   /* Only signal errors for file descriptors out of range.  */
 169                   if (action->action.close_action.fd < 0
 170                       || action->action.close_action.fd >= fdlimit.rlim_cur)
 171                     goto fail;
 172                 }
 173               break;
 174
 175             case spawn_do_open:
 176               {
 177                 /* POSIX states that if fildes was already an open file descriptor,
 178                    it shall be closed before the new file is opened.  This avoid
 179                    pontential issues when posix_spawn plus addopen action is called
 180                    with the process already at maximum number of file descriptor
 181                    opened and also for multiple actions on single-open special
 182                    paths (like /dev/watchdog).  */
 183                 __close_nocancel (action->action.open_action.fd);
 184
 185                 int new_fd = __open_nocancel (action->action.open_action.path,
 186                                               action->action.open_action.oflag
 187                                               | O_LARGEFILE,
 188                                               action->action.open_action.mode);
 189
 190                 if (new_fd == -1)
 191                   goto fail;
 192
 193                 /* Make sure the desired file descriptor is used.  */
 194                 if (new_fd != action->action.open_action.fd)
 195                   {
 196                     if (__dup2 (new_fd, action->action.open_action.fd)
 197                         != action->action.open_action.fd)
 198                       goto fail;
 199
 200                     if (__close_nocancel (new_fd) != 0)
 201                       goto fail;
 202                   }
 203               }
 204               break;
 205
 206             case spawn_do_dup2:
 207               if (__dup2 (action->action.dup2_action.fd,
 208                           action->action.dup2_action.newfd)
 209                   != action->action.dup2_action.newfd)
 210                 goto fail;
 211               break;
 212
 213             case spawn_do_chdir:
 214               if (__chdir (action->action.chdir_action.path) != 0)
 215                 goto fail;
 216               break;
 217
 218             case spawn_do_fchdir:
 219               if (__fchdir (action->action.fchdir_action.fd) != 0)
 220                 goto fail;
 221               break;
 222             }
 223         }
 224     }
 225
 226   /* Set the initial signal mask of the child if POSIX_SPAWN_SETSIGMASK
 227      is set, otherwise restore the previous one.  */
 228   __sigprocmask (SIG_SETMASK, (attr->__flags & POSIX_SPAWN_SETSIGMASK)
 229                  ? &attr->__ss : &args->oldmask, 0);
 230
 231   args->exec (args->file, args->argv, args->envp);
 232
 233   /* This is compatibility function required to enable posix_spawn run
 234      script without shebang definition for older posix_spawn versions
 235      (2.15).  */
 236   maybe_script_execute (args);
 237
 238 fail:
 239   /* errno should have an appropriate non-zero value; otherwise,
 240      there's a bug in glibc or the kernel.  For lack of an error code
 241      (EINTERNALBUG) describing that, use ECHILD.  Another option would
 242      be to set args->err to some negative sentinel and have the parent
 243      abort(), but that seems needlessly harsh.  */
 244   ret = errno ? : ECHILD;
 245   if (ret)
 246     /* Since sizeof errno < PIPE_BUF, the write is atomic. */
 247     while (__write_nocancel (args->pipe[1], &ret, sizeof (ret)) < 0);
 248
 249   _exit (SPAWN_ERROR);
 250 }
 251
 252 /* Spawn a new process executing PATH with the attributes describes in *ATTRP.
 253    Before running the process perform the actions described in FILE-ACTIONS. */
 254 int
 255 __spawnix (pid_t *pid, const char *file,
 256            const posix_spawn_file_actions_t *file_actions,
 257            const posix_spawnattr_t *attrp, char *const argv[],
 258            char *const envp[], int xflags,
 259            int (*exec) (const char *, char *const *, char *const *))
 260 {
 261   struct posix_spawn_args args;
 262   int ec;
 263
 264   if (__pipe2 (args.pipe, O_CLOEXEC))
 265     return errno;
 266
 267   /* Disable asynchronous cancellation.  */
 268   int state;
 269   __libc_ptf_call (__pthread_setcancelstate,
 270                    (PTHREAD_CANCEL_DISABLE, &state), 0);
 271
 272   ptrdiff_t argc = 0;
 273   ptrdiff_t limit = INT_MAX - 1;
 274   while (argv[argc++] != NULL)
 275     if (argc == limit)
 276       {
 277         errno = E2BIG;
 278         return errno;
 279       }
 280
 281   args.file = file;
 282   args.exec = exec;
 283   args.fa = file_actions;
 284   args.attr = attrp ? attrp : &(const posix_spawnattr_t) { 0 };
 285   args.argv = argv;
 286   args.argc = argc;
 287   args.envp = envp;
 288   args.xflags = xflags;
 289
 290   /* Generate the new process.  */
 291   pid_t new_pid = __fork ();
 292
 293   if (new_pid == 0)
 294     __spawni_child (&args);
 295   else if (new_pid > 0)
 296     {
 297       __close (args.pipe[1]);
 298
 299       if (__read (args.pipe[0], &ec, sizeof ec) != sizeof ec)
 300         ec = 0;
 301       else
 302         __waitpid (new_pid, &(int) { 0 }, 0);
 303     }
 304   else
 305     ec = errno;
 306
 307   __close (args.pipe[0]);
 308
 309   if ((ec == 0) && (pid != NULL))
 310     *pid = new_pid;
 311
 312   __libc_ptf_call (__pthread_setcancelstate, (state, NULL), 0);
 313
 314   return ec;
 315 }
 316
 317 int
 318 __spawni (pid_t * pid, const char *file,
 319           const posix_spawn_file_actions_t * acts,
 320           const posix_spawnattr_t * attrp, char *const argv[],
 321           char *const envp[], int xflags)
 322 {
 323   /* It uses __execvpex to avoid run ENOEXEC in non compatibility mode (it
 324      will be handled by maybe_script_execute).  */
 325   return __spawnix (pid, file, acts, attrp, argv, envp, xflags,
 326                     xflags & SPAWN_XFLAGS_USE_PATH ? __execvpex : __execve);
 327 }