support/support_capture_subprocess.c

   1 /* Capture output from a subprocess.
   2    Copyright (C) 2017-2024 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 <support/subprocess.h>
  20 #include <support/capture_subprocess.h>
  21
  22 #include <errno.h>
  23 #include <fcntl.h>
  24 #include <stdlib.h>
  25 #include <support/check.h>
  26 #include <support/xunistd.h>
  27 #include <support/xsocket.h>
  28 #include <support/xspawn.h>
  29 #include <support/support.h>
  30 #include <support/test-driver.h>
  31
  32 static void
  33 transfer (const char *what, struct pollfd *pfd, struct xmemstream *stream)
  34 {
  35   if (pfd->revents != 0)
  36     {
  37       char buf[1024];
  38       ssize_t ret = TEMP_FAILURE_RETRY (read (pfd->fd, buf, sizeof (buf)));
  39       if (ret < 0)
  40         {
  41           support_record_failure ();
  42           printf ("error: reading from subprocess %s: %m\n", what);
  43           pfd->events = 0;
  44           pfd->revents = 0;
  45         }
  46       else if (ret == 0)
  47         {
  48           /* EOF reached.  Stop listening.  */
  49           pfd->events = 0;
  50           pfd->revents = 0;
  51         }
  52       else
  53         /* Store the data just read.   */
  54         TEST_VERIFY (fwrite (buf, ret, 1, stream->out) == 1);
  55     }
  56 }
  57
  58 static void
  59 support_capture_poll (struct support_capture_subprocess *result,
  60                       struct support_subprocess *proc)
  61 {
  62   struct pollfd fds[2] =
  63     {
  64       { .fd = proc->stdout_pipe[0], .events = POLLIN },
  65       { .fd = proc->stderr_pipe[0], .events = POLLIN },
  66     };
  67
  68   do
  69     {
  70       xpoll (fds, 2, -1);
  71       transfer ("stdout", &fds[0], &result->out);
  72       transfer ("stderr", &fds[1], &result->err);
  73     }
  74   while (fds[0].events != 0 || fds[1].events != 0);
  75
  76   xfclose_memstream (&result->out);
  77   xfclose_memstream (&result->err);
  78
  79   result->status = support_process_wait (proc);
  80 }
  81
  82 struct support_capture_subprocess
  83 support_capture_subprocess (void (*callback) (void *), void *closure)
  84 {
  85   struct support_capture_subprocess result;
  86   xopen_memstream (&result.out);
  87   xopen_memstream (&result.err);
  88
  89   struct support_subprocess proc = support_subprocess (callback, closure);
  90
  91   support_capture_poll (&result, &proc);
  92   return result;
  93 }
  94
  95 struct support_capture_subprocess
  96 support_capture_subprogram (const char *file, char *const argv[],
  97                             char *const envp[])
  98 {
  99   struct support_capture_subprocess result;
 100   xopen_memstream (&result.out);
 101   xopen_memstream (&result.err);
 102
 103   struct support_subprocess proc = support_subprogram (file, argv, envp);
 104
 105   support_capture_poll (&result, &proc);
 106   return result;
 107 }
 108
 109 /* Copies the executable into a restricted directory, so that we can
 110    safely make it SGID with the TARGET group ID.  Then runs the
 111    executable.  */
 112 static int
 113 copy_and_spawn_sgid (char *child_id, gid_t gid)
 114 {
 115   char *dirname = xasprintf ("%s/tst-tunables-setuid.%jd",
 116                              test_dir, (intmax_t) getpid ());
 117   char *execname = xasprintf ("%s/bin", dirname);
 118   int infd = -1;
 119   int outfd = -1;
 120   int ret = 1, status = 1;
 121
 122   TEST_VERIFY (mkdir (dirname, 0700) == 0);
 123   if (support_record_failure_is_failed ())
 124     goto err;
 125
 126   infd = open ("/proc/self/exe", O_RDONLY);
 127   if (infd < 0)
 128     FAIL_UNSUPPORTED ("unsupported: Cannot read binary from procfs\n");
 129
 130   outfd = open (execname, O_WRONLY | O_CREAT | O_EXCL, 0700);
 131   TEST_VERIFY (outfd >= 0);
 132   if (support_record_failure_is_failed ())
 133     goto err;
 134
 135   char buf[4096];
 136   for (;;)
 137     {
 138       ssize_t rdcount = read (infd, buf, sizeof (buf));
 139       TEST_VERIFY (rdcount >= 0);
 140       if (support_record_failure_is_failed ())
 141         goto err;
 142       if (rdcount == 0)
 143         break;
 144       char *p = buf;
 145       char *end = buf + rdcount;
 146       while (p != end)
 147         {
 148           ssize_t wrcount = write (outfd, buf, end - p);
 149           if (wrcount == 0)
 150             errno = ENOSPC;
 151           TEST_VERIFY (wrcount > 0);
 152           if (support_record_failure_is_failed ())
 153             goto err;
 154           p += wrcount;
 155         }
 156     }
 157
 158   bool chowned = false;
 159   TEST_VERIFY ((chowned = fchown (outfd, getuid (), gid) == 0)
 160                || errno == EPERM);
 161   if (support_record_failure_is_failed ())
 162     goto err;
 163   else if (!chowned)
 164     {
 165       ret = 77;
 166       goto err;
 167     }
 168
 169   TEST_VERIFY (fchmod (outfd, 02750) == 0);
 170   if (support_record_failure_is_failed ())
 171     goto err;
 172   TEST_VERIFY (close (outfd) == 0);
 173   if (support_record_failure_is_failed ())
 174     goto err;
 175   TEST_VERIFY (close (infd) == 0);
 176   if (support_record_failure_is_failed ())
 177     goto err;
 178
 179   /* We have the binary, now spawn the subprocess.  Avoid using
 180      support_subprogram because we only want the program exit status, not the
 181      contents.  */
 182   ret = 0;
 183   infd = outfd = -1;
 184
 185   char * const args[] = {execname, child_id, NULL};
 186
 187   status = support_subprogram_wait (args[0], args);
 188
 189 err:
 190   if (outfd >= 0)
 191     close (outfd);
 192   if (infd >= 0)
 193     close (infd);
 194   if (execname != NULL)
 195     {
 196       unlink (execname);
 197       free (execname);
 198     }
 199   if (dirname != NULL)
 200     {
 201       rmdir (dirname);
 202       free (dirname);
 203     }
 204
 205   if (ret == 77)
 206     FAIL_UNSUPPORTED ("Failed to make sgid executable for test\n");
 207   if (ret != 0)
 208     FAIL_EXIT1 ("Failed to make sgid executable for test\n");
 209
 210   return status;
 211 }
 212
 213 int
 214 support_capture_subprogram_self_sgid (char *child_id)
 215 {
 216   gid_t target = 0;
 217   const int count = 64;
 218   gid_t groups[count];
 219
 220   /* Get a GID which is not our current GID, but is present in the
 221      supplementary group list.  */
 222   int ret = getgroups (count, groups);
 223   if (ret < 0)
 224     FAIL_UNSUPPORTED("Could not get group list for user %jd\n",
 225                      (intmax_t) getuid ());
 226
 227   gid_t current = getgid ();
 228   for (int i = 0; i < ret; ++i)
 229     {
 230       if (groups[i] != current)
 231         {
 232           target = groups[i];
 233           break;
 234         }
 235     }
 236
 237   if (target == 0)
 238     FAIL_UNSUPPORTED("Could not find a suitable GID for user %jd\n",
 239                      (intmax_t) getuid ());
 240
 241   return copy_and_spawn_sgid (child_id, target);
 242 }
 243
 244 void
 245 support_capture_subprocess_free (struct support_capture_subprocess *p)
 246 {
 247   free (p->out.buffer);
 248   free (p->err.buffer);
 249 }