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authorAdhemerval Zanella <adhemerval.zanella@linaro.org>2020-12-29 12:24:28 -0300
committerAdhemerval Zanella <adhemerval.zanella@linaro.org>2021-01-20 11:13:53 -0300
commit961d7cff51332b7b4ed98d4530a98f73355dda4b (patch)
treea99241d06c8e58419c5bf65f14f149aa2620f4b3 /stdlib/tst-canon-bz26341.c
parent1006250ea2d683e684f65911d738bd84f55c06c1 (diff)
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stdlib: Add testcase for BZ #26241
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>
Diffstat (limited to 'stdlib/tst-canon-bz26341.c')
-rw-r--r--stdlib/tst-canon-bz26341.c101
1 files changed, 101 insertions, 0 deletions
diff --git a/stdlib/tst-canon-bz26341.c b/stdlib/tst-canon-bz26341.c
new file mode 100644
index 0000000000..6d054596b5
--- /dev/null
+++ b/stdlib/tst-canon-bz26341.c
@@ -0,0 +1,101 @@
+/* Check if realpath does not consume extra stack space based on symlink
+   existance in the path (BZ #26341)
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <stdlib.h>
+#include <string.h>
+#include <sys/param.h>
+#include <unistd.h>
+
+#define __sysconf sysconf
+#include <eloop-threshold.h>
+#include <support/check.h>
+#include <support/support.h>
+#include <support/temp_file.h>
+#include <support/xunistd.h>
+#include <support/xthread.h>
+
+static char *filename;
+static size_t filenamelen;
+static char *linkname;
+
+#ifndef PATH_MAX
+# define PATH_MAX 1024
+#endif
+
+static void
+create_link (void)
+{
+  int fd = create_temp_file ("tst-canon-bz26341", &filename);
+  TEST_VERIFY_EXIT (fd != -1);
+  xclose (fd);
+
+  /* Create MAXLINKS symbolic links to the temporary filename.
+     On exit, linkname has the last link created.  */
+  char *prevlink = filename;
+  int maxlinks = __eloop_threshold ();
+  for (int i = 0; i < maxlinks; i++)
+    {
+      linkname = xasprintf ("%s%d", filename, i);
+      xsymlink (prevlink, linkname);
+      add_temp_file (linkname);
+      prevlink = linkname;
+    }
+
+  filenamelen = strlen (filename);
+}
+
+static void *
+do_realpath (void *arg)
+{
+  /* 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.
+     This stack allocations tries fill the thread allocated stack minus
+     both the resolved path (plus some slack) and the realpath (plus some
+     slack).
+     If realpath uses more than 2 * PATH_MAX plus some slack it will trigger
+     a stackoverflow.  */
+
+  const size_t realpath_usage = 2 * PATH_MAX + 1024;
+  const size_t thread_usage = 1 * PATH_MAX + 1024;
+  size_t stack_size = support_small_thread_stack_size ()
+		      - realpath_usage - thread_usage;
+  char stack[stack_size];
+  char *resolved = stack + stack_size - thread_usage + 1024;
+
+  char *p = realpath (linkname, resolved);
+  TEST_VERIFY (p != NULL);
+  TEST_COMPARE_BLOB (resolved, filenamelen, filename, filenamelen);
+
+  return NULL;
+}
+
+static int
+do_test (void)
+{
+  create_link ();
+
+  pthread_t th = xpthread_create (support_small_stack_thread_attribute (),
+				  do_realpath, NULL);
+  xpthread_join (th);
+
+  return 0;
+}
+
+#include <support/test-driver.c>