commit 5460617d1567657621107d895ee2dd83bc1f88f2

Author: Paul Pluzhnikov <ppluzhnikov@google.com>

Date:   Tue May 8 18:12:41 2018 -0700

    Fix BZ 22786: integer addition overflow may cause stack buffer overflow

    when realpath() input length is close to SSIZE_MAX.

    2018-05-09  Paul Pluzhnikov  <ppluzhnikov@google.com>

            [BZ #22786]

            * stdlib/canonicalize.c (__realpath): Fix overflow in path length

            computation.

            * stdlib/Makefile (test-bz22786): New test.

            * stdlib/test-bz22786.c: New test.

diff --git a/stdlib/Makefile b/stdlib/Makefile

index b5553eafc2a4bbd5..7265b44a5082b991 100644

--- a/stdlib/Makefile

+++ b/stdlib/Makefile

@@ -72,7 +72,7 @@ tests		:= tst-strtol tst-strtod testmb testrand testsort testdiv   \

 		   tst-makecontext3 bug-getcontext bug-fmtmsg1		    \

 		   tst-secure-getenv tst-strtod-overflow tst-strtod-round   \

 		   tst-tininess tst-strtod-underflow tst-strfmon_l	    \

-		   tst-makecontext-align

+		   tst-makecontext-align test-bz22786

 tests-static	:= tst-secure-getenv

 include ../Makeconfig

diff --git a/stdlib/canonicalize.c b/stdlib/canonicalize.c

index aeff804c108de277..b43f6223b98a578a 100644

--- a/stdlib/canonicalize.c

+++ b/stdlib/canonicalize.c

@@ -181,7 +181,7 @@ __realpath (const char *name, char *resolved)

 		extra_buf = __alloca (path_max);

 	      len = strlen (end);

-	      if ((long int) (n + len) >= path_max)

+	      if (path_max - n <= len)

 		{

 		  __set_errno (ENAMETOOLONG);

 		  goto error;

diff --git a/stdlib/test-bz22786.c b/stdlib/test-bz22786.c

new file mode 100644

index 0000000000000000..e7837f98c19fc4bf

--- /dev/null

+++ b/stdlib/test-bz22786.c

@@ -0,0 +1,90 @@

+/* Bug 22786: test for buffer overflow in realpath.

+   Copyright (C) 2018 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

+   <http://www.gnu.org/licenses/>.  */

+

+/* This file must be run from within a directory called "stdlib".  */

+

+#include <errno.h>

+#include <limits.h>

+#include <stdio.h>

+#include <stdlib.h>

+#include <string.h>

+#include <unistd.h>

+#include <sys/stat.h>

+#include <sys/types.h>

+#include <support/test-driver.h>

+#include <libc-diag.h>

+

+static int

+do_test (void)

+{

+  const char dir[] = "bz22786";

+  const char lnk[] = "bz22786/symlink";

+

+  rmdir (dir);

+  if (mkdir (dir, 0755) != 0 && errno != EEXIST)

+    {

+      printf ("mkdir %s: %m\n", dir);

+      return EXIT_FAILURE;

+    }

+  if (symlink (".", lnk) != 0 && errno != EEXIST)

+    {

+      printf ("symlink (%s, %s): %m\n", dir, lnk);

+      return EXIT_FAILURE;

+    }

+

+  const size_t path_len = (size_t) INT_MAX + 1;

+

+  DIAG_PUSH_NEEDS_COMMENT;

+#if __GNUC_PREREQ (7, 0)

+  /* GCC 7 warns about too-large allocations; here we need such

+     allocation to succeed for the test to work.  */

+  DIAG_IGNORE_NEEDS_COMMENT (7, "-Walloc-size-larger-than=");

+#endif

+  char *path = malloc (path_len);

+  DIAG_POP_NEEDS_COMMENT;

+

+  if (path == NULL)

+    {

+      printf ("malloc (%zu): %m\n", path_len);

+      return EXIT_UNSUPPORTED;

+    }

+

+  /* Construct very long path = "bz22786/symlink/aaaa....."  */

+  char *p = mempcpy (path, lnk, sizeof (lnk) - 1);

+  *(p++) = '/';

+  memset (p, 'a', path_len - (path - p) - 2);

+  p[path_len - (path - p) - 1] = '\0';

+

+  /* This call crashes before the fix for bz22786 on 32-bit platforms.  */

+  p = realpath (path, NULL);

+

+  if (p != NULL || errno != ENAMETOOLONG)

+    {

+      printf ("realpath: %s (%m)", p);

+      return EXIT_FAILURE;

+    }

+

+  /* Cleanup.  */

+  unlink (lnk);

+  rmdir (dir);

+

+  return 0;

+}

+

+#define TEST_FUNCTION do_test

+#include <support/test-driver.c>