sysdeps/posix/spawni.c

   1 /* Guts of POSIX spawn interface.  Generic POSIX.1 version.
   2    Copyright (C) 2000-2021 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    <https://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               /* Austin Group issue #411 requires adddup2 action with source
 208                  and destination being equal to remove close-on-exec flag.  */
 209               if (action->action.dup2_action.fd
 210                   == action->action.dup2_action.newfd)
 211                 {
 212                   int fd = action->action.dup2_action.newfd;
 213                   int flags = __fcntl (fd, F_GETFD, 0);
 214                   if (flags == -1)
 215                     goto fail;
 216                   if (__fcntl (fd, F_SETFD, flags & ~FD_CLOEXEC) == -1)
 217                     goto fail;
 218                 }
 219               else if (__dup2 (action->action.dup2_action.fd,
 220                                action->action.dup2_action.newfd)
 221                        != action->action.dup2_action.newfd)
 222                 goto fail;
 223               break;
 224
 225             case spawn_do_chdir:
 226               if (__chdir (action->action.chdir_action.path) != 0)
 227                 goto fail;
 228               break;
 229
 230             case spawn_do_fchdir:
 231               if (__fchdir (action->action.fchdir_action.fd) != 0)
 232                 goto fail;
 233               break;
 234             }
 235         }
 236     }
 237
 238   /* Set the initial signal mask of the child if POSIX_SPAWN_SETSIGMASK
 239      is set, otherwise restore the previous one.  */
 240   __sigprocmask (SIG_SETMASK, (attr->__flags & POSIX_SPAWN_SETSIGMASK)
 241                  ? &attr->__ss : &args->oldmask, 0);
 242
 243   args->exec (args->file, args->argv, args->envp);
 244
 245   /* This is compatibility function required to enable posix_spawn run
 246      script without shebang definition for older posix_spawn versions
 247      (2.15).  */
 248   maybe_script_execute (args);
 249
 250 fail:
 251   /* errno should have an appropriate non-zero value; otherwise,
 252      there's a bug in glibc or the kernel.  For lack of an error code
 253      (EINTERNALBUG) describing that, use ECHILD.  Another option would
 254      be to set args->err to some negative sentinel and have the parent
 255      abort(), but that seems needlessly harsh.  */
 256   ret = errno ? : ECHILD;
 257   if (ret)
 258     /* Since sizeof errno < PIPE_BUF, the write is atomic. */
 259     while (__write_nocancel (args->pipe[1], &ret, sizeof (ret)) < 0);
 260
 261   _exit (SPAWN_ERROR);
 262 }
 263
 264 /* Spawn a new process executing PATH with the attributes describes in *ATTRP.
 265    Before running the process perform the actions described in FILE-ACTIONS. */
 266 int
 267 __spawnix (pid_t *pid, const char *file,
 268            const posix_spawn_file_actions_t *file_actions,
 269            const posix_spawnattr_t *attrp, char *const argv[],
 270            char *const envp[], int xflags,
 271            int (*exec) (const char *, char *const *, char *const *))
 272 {
 273   struct posix_spawn_args args;
 274   int ec;
 275
 276   if (__pipe2 (args.pipe, O_CLOEXEC))
 277     return errno;
 278
 279   /* Disable asynchronous cancellation.  */
 280   int state;
 281   __libc_ptf_call (__pthread_setcancelstate,
 282                    (PTHREAD_CANCEL_DISABLE, &state), 0);
 283
 284   ptrdiff_t argc = 0;
 285   ptrdiff_t limit = INT_MAX - 1;
 286   while (argv[argc++] != NULL)
 287     if (argc == limit)
 288       {
 289         errno = E2BIG;
 290         return errno;
 291       }
 292
 293   args.file = file;
 294   args.exec = exec;
 295   args.fa = file_actions;
 296   args.attr = attrp ? attrp : &(const posix_spawnattr_t) { 0 };
 297   args.argv = argv;
 298   args.argc = argc;
 299   args.envp = envp;
 300   args.xflags = xflags;
 301
 302   /* Generate the new process.  */
 303   pid_t new_pid = __fork ();
 304
 305   if (new_pid == 0)
 306     __spawni_child (&args);
 307   else if (new_pid > 0)
 308     {
 309       __close (args.pipe[1]);
 310
 311       if (__read (args.pipe[0], &ec, sizeof ec) != sizeof ec)
 312         ec = 0;
 313       else
 314         __waitpid (new_pid, &(int) { 0 }, 0);
 315     }
 316   else
 317     ec = errno;
 318
 319   __close (args.pipe[0]);
 320
 321   if ((ec == 0) && (pid != NULL))
 322     *pid = new_pid;
 323
 324   __libc_ptf_call (__pthread_setcancelstate, (state, NULL), 0);
 325
 326   return ec;
 327 }
 328
 329 int
 330 __spawni (pid_t * pid, const char *file,
 331           const posix_spawn_file_actions_t * acts,
 332           const posix_spawnattr_t * attrp, char *const argv[],
 333           char *const envp[], int xflags)
 334 {
 335   /* It uses __execvpex to avoid run ENOEXEC in non compatibility mode (it
 336      will be handled by maybe_script_execute).  */
 337   return __spawnix (pid, file, acts, attrp, argv, envp, xflags,
 338                     xflags & SPAWN_XFLAGS_USE_PATH ? __execvpex : __execve);
 339 }