1/* POSIX spawn interface. Linux version.
2 Copyright (C) 2016-2019 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 <fcntl.h>
21#include <paths.h>
22#include <string.h>
23#include <sys/resource.h>
24#include <sys/wait.h>
25#include <sys/param.h>
26#include <sys/mman.h>
27#include <not-cancel.h>
28#include <local-setxid.h>
29#include <shlib-compat.h>
30#include <nptl/pthreadP.h>
31#include <dl-sysdep.h>
32#include <libc-pointer-arith.h>
33#include <ldsodefs.h>
34#include "spawn_int.h"
35
36/* The Linux implementation of posix_spawn{p} uses the clone syscall directly
37 with CLONE_VM and CLONE_VFORK flags and an allocated stack. The new stack
38 and start function solves most the vfork limitation (possible parent
39 clobber due stack spilling). The remaining issue are:
40
41 1. That no signal handlers must run in child context, to avoid corrupting
42 parent's state.
43 2. The parent must ensure child's stack freeing.
44 3. Child must synchronize with parent to enforce 2. and to possible
45 return execv issues.
46
47 The first issue is solved by blocking all signals in child, even
48 the NPTL-internal ones (SIGCANCEL and SIGSETXID). The second and
49 third issue is done by a stack allocation in parent, and by using a
50 field in struct spawn_args where the child can write an error
51 code. CLONE_VFORK ensures that the parent does not run until the
52 child has either exec'ed successfully or exited. */
53
54
55/* The Unix standard contains a long explanation of the way to signal
56 an error after the fork() was successful. Since no new wait status
57 was wanted there is no way to signal an error using one of the
58 available methods. The committee chose to signal an error by a
59 normal program exit with the exit code 127. */
60#define SPAWN_ERROR 127
61
62#ifdef __ia64__
63# define CLONE(__fn, __stackbase, __stacksize, __flags, __args) \
64 __clone2 (__fn, __stackbase, __stacksize, __flags, __args, 0, 0, 0)
65#else
66# define CLONE(__fn, __stack, __stacksize, __flags, __args) \
67 __clone (__fn, __stack, __flags, __args)
68#endif
69
70/* Since ia64 wants the stackbase w/clone2, re-use the grows-up macro. */
71#if _STACK_GROWS_UP || defined (__ia64__)
72# define STACK(__stack, __stack_size) (__stack)
73#elif _STACK_GROWS_DOWN
74# define STACK(__stack, __stack_size) (__stack + __stack_size)
75#endif
76
77
78struct posix_spawn_args
79{
80 sigset_t oldmask;
81 const char *file;
82 int (*exec) (const char *, char *const *, char *const *);
83 const posix_spawn_file_actions_t *fa;
84 const posix_spawnattr_t *restrict attr;
85 char *const *argv;
86 ptrdiff_t argc;
87 char *const *envp;
88 int xflags;
89 int err;
90};
91
92/* Older version requires that shell script without shebang definition
93 to be called explicitly using /bin/sh (_PATH_BSHELL). */
94static void
95maybe_script_execute (struct posix_spawn_args *args)
96{
97 if (SHLIB_COMPAT (libc, GLIBC_2_2, GLIBC_2_15)
98 && (args->xflags & SPAWN_XFLAGS_TRY_SHELL) && errno == ENOEXEC)
99 {
100 char *const *argv = args->argv;
101 ptrdiff_t argc = args->argc;
102
103 /* Construct an argument list for the shell. */
104 char *new_argv[argc + 2];
105 new_argv[0] = (char *) _PATH_BSHELL;
106 new_argv[1] = (char *) args->file;
107 if (argc > 1)
108 memcpy (new_argv + 2, argv + 1, argc * sizeof (char *));
109 else
110 new_argv[2] = NULL;
111
112 /* Execute the shell. */
113 args->exec (new_argv[0], new_argv, args->envp);
114 }
115}
116
117/* Function used in the clone call to setup the signals mask, posix_spawn
118 attributes, and file actions. It run on its own stack (provided by the
119 posix_spawn call). */
120static int
121__spawni_child (void *arguments)
122{
123 struct posix_spawn_args *args = arguments;
124 const posix_spawnattr_t *restrict attr = args->attr;
125 const posix_spawn_file_actions_t *file_actions = args->fa;
126
127 /* The child must ensure that no signal handler are enabled because it shared
128 memory with parent, so the signal disposition must be either SIG_DFL or
129 SIG_IGN. It does by iterating over all signals and although it could
130 possibly be more optimized (by tracking which signal potentially have a
131 signal handler), it might requires system specific solutions (since the
132 sigset_t data type can be very different on different architectures). */
133 struct sigaction sa;
134 memset (&sa, '\0', sizeof (sa));
135
136 sigset_t hset;
137 __sigprocmask (SIG_BLOCK, 0, &hset);
138 for (int sig = 1; sig < _NSIG; ++sig)
139 {
140 if ((attr->__flags & POSIX_SPAWN_SETSIGDEF)
141 && __sigismember (&attr->__sd, sig))
142 {
143 sa.sa_handler = SIG_DFL;
144 }
145 else if (__sigismember (&hset, sig))
146 {
147 if (__is_internal_signal (sig))
148 sa.sa_handler = SIG_IGN;
149 else
150 {
151 __libc_sigaction (sig, 0, &sa);
152 if (sa.sa_handler == SIG_IGN)
153 continue;
154 sa.sa_handler = SIG_DFL;
155 }
156 }
157 else
158 continue;
159
160 __libc_sigaction (sig, &sa, 0);
161 }
162
163#ifdef _POSIX_PRIORITY_SCHEDULING
164 /* Set the scheduling algorithm and parameters. */
165 if ((attr->__flags & (POSIX_SPAWN_SETSCHEDPARAM | POSIX_SPAWN_SETSCHEDULER))
166 == POSIX_SPAWN_SETSCHEDPARAM)
167 {
168 if (__sched_setparam (0, &attr->__sp) == -1)
169 goto fail;
170 }
171 else if ((attr->__flags & POSIX_SPAWN_SETSCHEDULER) != 0)
172 {
173 if (__sched_setscheduler (0, attr->__policy, &attr->__sp) == -1)
174 goto fail;
175 }
176#endif
177
178 if ((attr->__flags & POSIX_SPAWN_SETSID) != 0
179 && __setsid () < 0)
180 goto fail;
181
182 /* Set the process group ID. */
183 if ((attr->__flags & POSIX_SPAWN_SETPGROUP) != 0
184 && __setpgid (0, attr->__pgrp) != 0)
185 goto fail;
186
187 /* Set the effective user and group IDs. */
188 if ((attr->__flags & POSIX_SPAWN_RESETIDS) != 0
189 && (local_seteuid (__getuid ()) != 0
190 || local_setegid (__getgid ()) != 0))
191 goto fail;
192
193 /* Execute the file actions. */
194 if (file_actions != 0)
195 {
196 int cnt;
197 struct rlimit64 fdlimit;
198 bool have_fdlimit = false;
199
200 for (cnt = 0; cnt < file_actions->__used; ++cnt)
201 {
202 struct __spawn_action *action = &file_actions->__actions[cnt];
203
204 switch (action->tag)
205 {
206 case spawn_do_close:
207 if (__close_nocancel (action->action.close_action.fd) != 0)
208 {
209 if (!have_fdlimit)
210 {
211 __getrlimit64 (RLIMIT_NOFILE, &fdlimit);
212 have_fdlimit = true;
213 }
214
215 /* Signal errors only for file descriptors out of range. */
216 if (action->action.close_action.fd < 0
217 || action->action.close_action.fd >= fdlimit.rlim_cur)
218 goto fail;
219 }
220 break;
221
222 case spawn_do_open:
223 {
224 /* POSIX states that if fildes was already an open file descriptor,
225 it shall be closed before the new file is opened. This avoid
226 pontential issues when posix_spawn plus addopen action is called
227 with the process already at maximum number of file descriptor
228 opened and also for multiple actions on single-open special
229 paths (like /dev/watchdog). */
230 __close_nocancel (action->action.open_action.fd);
231
232 int ret = __open_nocancel (action->action.open_action.path,
233 action->action.
234 open_action.oflag | O_LARGEFILE,
235 action->action.open_action.mode);
236
237 if (ret == -1)
238 goto fail;
239
240 int new_fd = ret;
241
242 /* Make sure the desired file descriptor is used. */
243 if (ret != action->action.open_action.fd)
244 {
245 if (__dup2 (new_fd, action->action.open_action.fd)
246 != action->action.open_action.fd)
247 goto fail;
248
249 if (__close_nocancel (new_fd) != 0)
250 goto fail;
251 }
252 }
253 break;
254
255 case spawn_do_dup2:
256 /* Austin Group issue #411 requires adddup2 action with source
257 and destination being equal to remove close-on-exec flag. */
258 if (action->action.dup2_action.fd
259 == action->action.dup2_action.newfd)
260 {
261 int fd = action->action.dup2_action.newfd;
262 int flags = __fcntl (fd, F_GETFD, 0);
263 if (flags == -1)
264 goto fail;
265 if (__fcntl (fd, F_SETFD, flags & ~FD_CLOEXEC) == -1)
266 goto fail;
267 }
268 else if (__dup2 (action->action.dup2_action.fd,
269 action->action.dup2_action.newfd)
270 != action->action.dup2_action.newfd)
271 goto fail;
272 break;
273
274 case spawn_do_chdir:
275 if (__chdir (action->action.chdir_action.path) != 0)
276 goto fail;
277 break;
278
279 case spawn_do_fchdir:
280 if (__fchdir (action->action.fchdir_action.fd) != 0)
281 goto fail;
282 break;
283 }
284 }
285 }
286
287 /* Set the initial signal mask of the child if POSIX_SPAWN_SETSIGMASK
288 is set, otherwise restore the previous one. */
289 __sigprocmask (SIG_SETMASK, (attr->__flags & POSIX_SPAWN_SETSIGMASK)
290 ? &attr->__ss : &args->oldmask, 0);
291
292 args->exec (args->file, args->argv, args->envp);
293
294 /* This is compatibility function required to enable posix_spawn run
295 script without shebang definition for older posix_spawn versions
296 (2.15). */
297 maybe_script_execute (args);
298
299fail:
300 /* errno should have an appropriate non-zero value; otherwise,
301 there's a bug in glibc or the kernel. For lack of an error code
302 (EINTERNALBUG) describing that, use ECHILD. Another option would
303 be to set args->err to some negative sentinel and have the parent
304 abort(), but that seems needlessly harsh. */
305 args->err = errno ? : ECHILD;
306 _exit (SPAWN_ERROR);
307}
308
309/* Spawn a new process executing PATH with the attributes describes in *ATTRP.
310 Before running the process perform the actions described in FILE-ACTIONS. */
311static int
312__spawnix (pid_t * pid, const char *file,
313 const posix_spawn_file_actions_t * file_actions,
314 const posix_spawnattr_t * attrp, char *const argv[],
315 char *const envp[], int xflags,
316 int (*exec) (const char *, char *const *, char *const *))
317{
318 pid_t new_pid;
319 struct posix_spawn_args args;
320 int ec;
321
322 /* To avoid imposing hard limits on posix_spawn{p} the total number of
323 arguments is first calculated to allocate a mmap to hold all possible
324 values. */
325 ptrdiff_t argc = 0;
326 /* Linux allows at most max (0x7FFFFFFF, 1/4 stack size) arguments
327 to be used in a execve call. We limit to INT_MAX minus one due the
328 compatiblity code that may execute a shell script (maybe_script_execute)
329 where it will construct another argument list with an additional
330 argument. */
331 ptrdiff_t limit = INT_MAX - 1;
332 while (argv[argc++] != NULL)
333 if (argc == limit)
334 {
335 errno = E2BIG;
336 return errno;
337 }
338
339 int prot = (PROT_READ | PROT_WRITE
340 | ((GL (dl_stack_flags) & PF_X) ? PROT_EXEC : 0));
341
342 /* Add a slack area for child's stack. */
343 size_t argv_size = (argc * sizeof (void *)) + 512;
344 /* We need at least a few pages in case the compiler's stack checking is
345 enabled. In some configs, it is known to use at least 24KiB. We use
346 32KiB to be "safe" from anything the compiler might do. Besides, the
347 extra pages won't actually be allocated unless they get used. */
348 argv_size += (32 * 1024);
349 size_t stack_size = ALIGN_UP (argv_size, GLRO(dl_pagesize));
350 void *stack = __mmap (NULL, stack_size, prot,
351 MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
352 if (__glibc_unlikely (stack == MAP_FAILED))
353 return errno;
354
355 /* Disable asynchronous cancellation. */
356 int state;
357 __libc_ptf_call (__pthread_setcancelstate,
358 (PTHREAD_CANCEL_DISABLE, &state), 0);
359
360 /* Child must set args.err to something non-negative - we rely on
361 the parent and child sharing VM. */
362 args.err = 0;
363 args.file = file;
364 args.exec = exec;
365 args.fa = file_actions;
366 args.attr = attrp ? attrp : &(const posix_spawnattr_t) { 0 };
367 args.argv = argv;
368 args.argc = argc;
369 args.envp = envp;
370 args.xflags = xflags;
371
372 __libc_signal_block_all (&args.oldmask);
373
374 /* The clone flags used will create a new child that will run in the same
375 memory space (CLONE_VM) and the execution of calling thread will be
376 suspend until the child calls execve or _exit.
377
378 Also since the calling thread execution will be suspend, there is not
379 need for CLONE_SETTLS. Although parent and child share the same TLS
380 namespace, there will be no concurrent access for TLS variables (errno
381 for instance). */
382 new_pid = CLONE (__spawni_child, STACK (stack, stack_size), stack_size,
383 CLONE_VM | CLONE_VFORK | SIGCHLD, &args);
384
385 /* It needs to collect the case where the auxiliary process was created
386 but failed to execute the file (due either any preparation step or
387 for execve itself). */
388 if (new_pid > 0)
389 {
390 /* Also, it handles the unlikely case where the auxiliary process was
391 terminated before calling execve as if it was successfully. The
392 args.err is set to 0 as default and changed to a positive value
393 only in case of failure, so in case of premature termination
394 due a signal args.err will remain zeroed and it will be up to
395 caller to actually collect it. */
396 ec = args.err;
397 if (ec > 0)
398 /* There still an unlikely case where the child is cancelled after
399 setting args.err, due to a positive error value. Also there is
400 possible pid reuse race (where the kernel allocated the same pid
401 to an unrelated process). Unfortunately due synchronization
402 issues where the kernel might not have the process collected
403 the waitpid below can not use WNOHANG. */
404 __waitpid (new_pid, NULL, 0);
405 }
406 else
407 ec = -new_pid;
408
409 __munmap (stack, stack_size);
410
411 if ((ec == 0) && (pid != NULL))
412 *pid = new_pid;
413
414 __libc_signal_restore_set (&args.oldmask);
415
416 __libc_ptf_call (__pthread_setcancelstate, (state, NULL), 0);
417
418 return ec;
419}
420
421/* Spawn a new process executing PATH with the attributes describes in *ATTRP.
422 Before running the process perform the actions described in FILE-ACTIONS. */
423int
424__spawni (pid_t * pid, const char *file,
425 const posix_spawn_file_actions_t * acts,
426 const posix_spawnattr_t * attrp, char *const argv[],
427 char *const envp[], int xflags)
428{
429 /* It uses __execvpex to avoid run ENOEXEC in non compatibility mode (it
430 will be handled by maybe_script_execute). */
431 return __spawnix (pid, file, acts, attrp, argv, envp, xflags,
432 xflags & SPAWN_XFLAGS_USE_PATH ? __execvpex :__execve);
433}
434