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961d7cff51
Old implementation of realpath allocates a PATH_MAX using alloca for each symlink in the path, leading to MAXSYMLINKS times PATH_MAX maximum stack usage. The test create a symlink with __eloop_threshold() loops and creates a thread with minimum stack size (obtained through support_small_stack_thread_attribute). The thread issues a stack allocations that fill the thread allocated stack minus some slack plus and the realpath usage (which assumes a bounded stack usage). If realpath uses more than about 2 * PATH_MAX plus some slack it triggers a stackoverflow. Checked on x86_64-linux-gnu and i686-linux-gnu. Reviewed-by: DJ Delorie <dj@redhat.com>
102 lines
2.9 KiB
C
102 lines
2.9 KiB
C
/* Check if realpath does not consume extra stack space based on symlink
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existance in the path (BZ #26341)
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Copyright (C) 2021 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <stdlib.h>
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#include <string.h>
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#include <sys/param.h>
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#include <unistd.h>
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#define __sysconf sysconf
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#include <eloop-threshold.h>
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#include <support/check.h>
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#include <support/support.h>
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#include <support/temp_file.h>
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#include <support/xunistd.h>
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#include <support/xthread.h>
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static char *filename;
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static size_t filenamelen;
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static char *linkname;
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#ifndef PATH_MAX
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# define PATH_MAX 1024
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#endif
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static void
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create_link (void)
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{
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int fd = create_temp_file ("tst-canon-bz26341", &filename);
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TEST_VERIFY_EXIT (fd != -1);
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xclose (fd);
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/* Create MAXLINKS symbolic links to the temporary filename.
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On exit, linkname has the last link created. */
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char *prevlink = filename;
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int maxlinks = __eloop_threshold ();
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for (int i = 0; i < maxlinks; i++)
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{
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linkname = xasprintf ("%s%d", filename, i);
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xsymlink (prevlink, linkname);
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add_temp_file (linkname);
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prevlink = linkname;
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}
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filenamelen = strlen (filename);
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}
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static void *
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do_realpath (void *arg)
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{
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/* Old implementation of realpath allocates a PATH_MAX using alloca
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for each symlink in the path, leading to MAXSYMLINKS times PATH_MAX
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maximum stack usage.
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This stack allocations tries fill the thread allocated stack minus
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both the resolved path (plus some slack) and the realpath (plus some
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slack).
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If realpath uses more than 2 * PATH_MAX plus some slack it will trigger
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a stackoverflow. */
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const size_t realpath_usage = 2 * PATH_MAX + 1024;
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const size_t thread_usage = 1 * PATH_MAX + 1024;
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size_t stack_size = support_small_thread_stack_size ()
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- realpath_usage - thread_usage;
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char stack[stack_size];
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char *resolved = stack + stack_size - thread_usage + 1024;
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char *p = realpath (linkname, resolved);
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TEST_VERIFY (p != NULL);
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TEST_COMPARE_BLOB (resolved, filenamelen, filename, filenamelen);
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return NULL;
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}
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static int
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do_test (void)
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{
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create_link ();
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pthread_t th = xpthread_create (support_small_stack_thread_attribute (),
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do_realpath, NULL);
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xpthread_join (th);
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return 0;
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}
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#include <support/test-driver.c>
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