stdlib/tst-canon-bz26341.c

   1 /* Check if realpath does not consume extra stack space based on symlink
   2    existence in the path (BZ #26341)
   3    Copyright (C) 2021-2024 Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <https://www.gnu.org/licenses/>.  */
  19
  20 #include <stdlib.h>
  21 #include <string.h>
  22 #include <sys/param.h>
  23 #include <unistd.h>
  24
  25 #define __sysconf sysconf
  26 #include <eloop-threshold.h>
  27 #include <support/check.h>
  28 #include <support/support.h>
  29 #include <support/temp_file.h>
  30 #include <support/xunistd.h>
  31 #include <support/xthread.h>
  32
  33 static char *filename;
  34 static size_t filenamelen;
  35 static char *linkname;
  36
  37 #ifndef PATH_MAX
  38 # define PATH_MAX 1024
  39 #endif
  40
  41 static void
  42 create_link (void)
  43 {
  44   int fd = create_temp_file ("tst-canon-bz26341", &filename);
  45   TEST_VERIFY_EXIT (fd != -1);
  46   xclose (fd);
  47
  48   /* Make filename a canonical path.  */
  49   char *saved_filename = filename;
  50   filename = realpath (filename, NULL);
  51   free (saved_filename);
  52   TEST_VERIFY (filename != NULL);
  53
  54   /* Create MAXLINKS symbolic links to the temporary filename.
  55      On exit, linkname has the last link created.  */
  56   char *prevlink = filename;
  57   int maxlinks = __eloop_threshold ();
  58   for (int i = 0; i < maxlinks; i++)
  59     {
  60       linkname = xasprintf ("%s%d", filename, i);
  61       xsymlink (prevlink, linkname);
  62       add_temp_file (linkname);
  63       prevlink = linkname;
  64     }
  65
  66   filenamelen = strlen (filename);
  67 }
  68
  69 static void *
  70 do_realpath (void *arg)
  71 {
  72   /* Old implementation of realpath allocates a PATH_MAX using alloca
  73      for each symlink in the path, leading to MAXSYMLINKS times PATH_MAX
  74      maximum stack usage.
  75      This stack allocations tries fill the thread allocated stack minus
  76      the resolved path (plus some slack), the realpath (plus some
  77      slack), and the system call usage (plus some slack).
  78      If realpath uses more than 2 * PATH_MAX plus some slack it will trigger
  79      a stackoverflow.  */
  80
  81   const size_t syscall_usage = 1 * PATH_MAX + 1024;
  82   const size_t realpath_usage = 2 * PATH_MAX + 1024;
  83   const size_t thread_usage = 1 * PATH_MAX + 1024;
  84   size_t stack_size = support_small_thread_stack_size ()
  85                       - syscall_usage - realpath_usage - thread_usage;
  86   char stack[stack_size];
  87   char *resolved = stack + stack_size - thread_usage + 1024;
  88
  89   char *p = realpath (linkname, resolved);
  90   TEST_VERIFY (p != NULL);
  91   TEST_COMPARE_BLOB (resolved, filenamelen, filename, filenamelen);
  92
  93   return NULL;
  94 }
  95
  96 static int
  97 do_test (void)
  98 {
  99   create_link ();
 100
 101   pthread_t th = xpthread_create (support_small_stack_thread_attribute (),
 102                                   do_realpath, NULL);
 103   xpthread_join (th);
 104
 105   return 0;
 106 }
 107
 108 #include <support/test-driver.c>