realpath: Set errno to ENAMETOOLONG for result larger than PATH_MAX [BZ #28770]

Message ID 20220113054203.3126818-1-siddhesh@sourceware.org
State New
Headers show
Series
  • realpath: Set errno to ENAMETOOLONG for result larger than PATH_MAX [BZ #28770]
Related show

Commit Message

Sunil K Pandey via Libc-alpha Jan. 13, 2022, 5:42 a.m.
realpath returns an allocated string when the result exceeds PATH_MAX,
which is unexpected when its second argument is not NULL.  This results
in the second argument (resolved) being uninitialized and also results
in a memory leak since the caller expects resolved to be the same as the
returned value.

Return NULL and set errno to ENAMETOOLONG if the result exceeds
PATH_MAX.  This fixes [BZ #28770], which is CVE-2021-3998.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

---
 stdlib/Makefile               |  1 +
 stdlib/canonicalize.c         | 12 +++++-
 stdlib/tst-realpath-toolong.c | 78 +++++++++++++++++++++++++++++++++++
 3 files changed, 89 insertions(+), 2 deletions(-)
 create mode 100644 stdlib/tst-realpath-toolong.c

-- 
2.33.1

Patch

diff --git a/stdlib/Makefile b/stdlib/Makefile
index 52e4d8cf19..897d4ea79d 100644
--- a/stdlib/Makefile
+++ b/stdlib/Makefile
@@ -108,6 +108,7 @@  tests		:=  bug-fmtmsg1 \
 		    tst-random \
 		    tst-random2 \
 		    tst-realpath \
+		    tst-realpath-toolong \
 		    tst-secure-getenv \
 		    tst-setcontext \
 		    tst-setcontext2 \
diff --git a/stdlib/canonicalize.c b/stdlib/canonicalize.c
index f36bdf4c76..732dc7ea46 100644
--- a/stdlib/canonicalize.c
+++ b/stdlib/canonicalize.c
@@ -400,8 +400,16 @@  realpath_stk (const char *name, char *resolved,
 
 error:
   *dest++ = '\0';
-  if (resolved != NULL && dest - rname <= get_path_max ())
-    rname = strcpy (resolved, rname);
+  if (resolved != NULL)
+    {
+      if (dest - rname <= get_path_max ())
+	rname = strcpy (resolved, rname);
+      else
+	{
+	  failed = true;
+	  __set_errno (ENAMETOOLONG);
+	}
+    }
 
 error_nomem:
   scratch_buffer_free (&extra_buffer);
diff --git a/stdlib/tst-realpath-toolong.c b/stdlib/tst-realpath-toolong.c
new file mode 100644
index 0000000000..9693127560
--- /dev/null
+++ b/stdlib/tst-realpath-toolong.c
@@ -0,0 +1,78 @@ 
+/* Verify that realpath returns NULL with ENAMETOOLONG if the result exceeds
+   NAME_MAX.
+   Copyright The GNU Toolchain Authors.
+   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 <errno.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <support/check.h>
+#include <support/temp_file.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#define BASENAME "tst-realpath-toolong."
+size_t nest_count;
+char dir[NAME_MAX + 1];
+
+int
+do_test (void)
+{
+  char *base = support_create_temp_directory (BASENAME);
+
+  TEST_VERIFY_EXIT (chdir (base) == 0);
+
+  memset (dir, 'X', sizeof (dir) - 1);
+  dir[NAME_MAX] = '\0';
+
+  /* Create directories and descend into them so that the final path is larger
+     than PATH_MAX.  */
+  for (nest_count = 0; nest_count <= PATH_MAX / sizeof (dir); nest_count++)
+    {
+      TEST_VERIFY_EXIT (mkdir (dir, S_IRWXU) == 0);
+      TEST_VERIFY_EXIT (chdir (dir) == 0);
+    }
+
+  char buf[PATH_MAX + 1];
+  const char * const res = realpath (".", buf);
+
+  /* canonicalize.c states that if the real path is >= PATH_MAX, then
+     realpath returns NULL and sets ENAMETOOLONG.  */
+  TEST_VERIFY_EXIT (res == NULL && errno == ENAMETOOLONG);
+
+  free (base);
+  return 0;
+}
+
+static void
+delete_subdirectories (const char *name)
+{
+  if (nest_count-- > 0)
+    delete_subdirectories (dir);
+  rmdir (dir);
+}
+
+static void
+do_cleanup (void)
+{
+  delete_subdirectories (BASENAME);
+}
+
+#define CLEANUP_HANDLER do_cleanup
+#include <support/test-driver.c>