CVE-2014-8121: Do not close NSS files database during iteration [BZ #18007]

Robin Hack discovered Samba would enter an infinite loop processing
certain quota-related requests.  We eventually tracked this down to a
glibc issue.

Running a (simplified) test case under strace shows that /etc/passwd
is continuously opened and closed:

…
open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
lseek(3, 0, SEEK_CUR)                   = 0
read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 2717
lseek(3, 2717, SEEK_SET)                = 2717
close(3)                                = 0
open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
lseek(3, 0, SEEK_CUR)                   = 0
lseek(3, 0, SEEK_SET)                   = 0
read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 2717
lseek(3, 2717, SEEK_SET)                = 2717
close(3)                                = 0
open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
lseek(3, 0, SEEK_CUR)                   = 0
…

The lookup function implementation in
nss/nss_files/files-XXX.c:DB_LOOKUP has code to prevent that.  It is
supposed skip closing the input file if it was already open.

  /* Reset file pointer to beginning or open file.  */			      \
  status = internal_setent (keep_stream);				      \
									      \
  if (status == NSS_STATUS_SUCCESS)					      \
    {									      \
      /* Tell getent function that we have repositioned the file pointer.  */ \
      last_use = getby;							      \
									      \
      while ((status = internal_getent (result, buffer, buflen, errnop	      \
					H_ERRNO_ARG EXTRA_ARGS_VALUE))	      \
	     == NSS_STATUS_SUCCESS)					      \
	{ break_if_match }						      \
									      \
      if (! keep_stream)						      \
	internal_endent ();						      \
    }									      \

keep_stream is initialized from the stayopen flag in internal_setent.
internal_setent is called from the set*ent implementation as:

  status = internal_setent (stayopen);

However, for non-host database, this flag is always 0, per the
STAYOPEN magic in nss/getXXent_r.c.

Thus, the fix is this:

-  status = internal_setent (stayopen);
+  status = internal_setent (1);

This is not a behavioral change even for the hosts database (where the
application can specify the stayopen flag) because with a call to
sethostent(0), the file handle is still not closed in the
implementation of gethostent.

diff --git a/ChangeLog b/ChangeLog
index 35106b5235d8678fbe01ecde31352b3ebfc7b78f..c32cf7ae792f6860c5a5c2ec1bd97d7cdcf7b32c 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2015-04-29  Florian Weimer  <fweimer@redhat.com>
+
+       [BZ #18007]
+       * nss/nss_files/files-XXX.c (CONCAT): Always enable stayopen.
+       (CVE-2014-8121)
+       * nss/tst-nss-getpwent.c: New file.
+       * nss/Makefile (tests): Add new test.
+
 2015-04-28  Joseph Myers  <joseph@codesourcery.com>
 
        [BZ #18346]

diff --git a/NEWS b/NEWS
index fc3911dc29fcc4f79793c33341325e64e45998df..58cf55930ba711a525a122c29c67b8694d95c910 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -13,10 +13,10 @@ Version 2.22
   16512, 16560, 16783, 16850, 17090, 17195, 17269, 17523, 17542, 17569,
   17588, 17596, 17620, 17621, 17628, 17631, 17711, 17715, 17776, 17779,
   17792, 17836, 17912, 17916, 17930, 17932, 17944, 17949, 17964, 17965,
-  17967, 17969, 17978, 17987, 17991, 17996, 17998, 17999, 18019, 18020,
-  18029, 18030, 18032, 18036, 18038, 18039, 18042, 18043, 18046, 18047,
-  18068, 18080, 18093, 18100, 18104, 18110, 18111, 18128, 18138, 18185,
-  18197, 18206, 18210, 18211, 18247, 18287, 18333, 18346.
+  17967, 17969, 17978, 17987, 17991, 17996, 17998, 17999, 18007, 18019,
+  18020, 18029, 18030, 18032, 18036, 18038, 18039, 18042, 18043, 18046,
+  18047, 18068, 18080, 18093, 18100, 18104, 18110, 18111, 18128, 18138,
+  18185, 18197, 18206, 18210, 18211, 18247, 18287, 18333, 18346.
 
 * Cache information can be queried via sysconf() function on s390 e.g. with
   _SC_LEVEL1_ICACHE_SIZE as argument.
@@ -43,6 +43,10 @@ Version 2.22
   Hat).  These updates cause user visible changes, such as the fix for bug
   17998.
 
+* CVE-2014-8121 The NSS files backend would reset the file pointer used by
+  the get*ent functions if any of the query functions for the same database
+  are used during the iteration, causing a denial-of-service condition in
+  some applications.
 \f
 Version 2.21
 

diff --git a/nss/Makefile b/nss/Makefile
index d75dad2ee648fe70b0ed531fcdedf7e8d6b5254f..65ab7b5419dce97942e2b2ccad53ba4de6d00285 100644 (file)
--- a/nss/Makefile
+++ b/nss/Makefile
@@ -47,7 +47,7 @@ install-bin             := getent makedb
 makedb-modules = xmalloc hash-string
 extra-objs             += $(makedb-modules:=.o)
 
-tests                  = test-netdb tst-nss-test1 test-digits-dots
+tests                  = test-netdb tst-nss-test1 test-digits-dots tst-nss-getpwent
 xtests                 = bug-erange
 
 # Specify rules for the nss_* modules.  We have some services.

diff --git a/nss/nss_files/files-XXX.c b/nss/nss_files/files-XXX.c
index a7a45e5b0e9f68f5ece6cdbb393d8701d1bb9bca..a7ce5ea97e80b06c1c39b4ca50aa7087e91a3e62 100644 (file)
--- a/nss/nss_files/files-XXX.c
+++ b/nss/nss_files/files-XXX.c
@@ -134,7 +134,7 @@ CONCAT(_nss_files_set,ENTNAME) (int stayopen)
 
   __libc_lock_lock (lock);
 
-  status = internal_setent (stayopen);
+  status = internal_setent (1);
 
   if (status == NSS_STATUS_SUCCESS && fgetpos (stream, &position) < 0)
     {

diff --git a/nss/tst-nss-getpwent.c b/nss/tst-nss-getpwent.c
new file mode 100644 (file)
index 0000000..f2e8abc
--- /dev/null
+++ b/nss/tst-nss-getpwent.c
@@ -0,0 +1,118 @@
+/* Copyright (C) 2015 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/>.  */
+
+#include <pwd.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int
+do_test (void)
+{
+  /* Count the number of entries in the password database, and fetch
+     data from the first and last entries.  */
+  size_t count = 0;
+  struct passwd * pw;
+  char *first_name = NULL;
+  uid_t first_uid = 0;
+  char *last_name = NULL;
+  uid_t last_uid = 0;
+  setpwent ();
+  while ((pw  = getpwent ()) != NULL)
+    {
+      if (first_name == NULL)
+       {
+         first_name = strdup (pw->pw_name);
+         if (first_name == NULL)
+           {
+             printf ("strdup: %m\n");
+             return 1;
+           }
+         first_uid = pw->pw_uid;
+       }
+
+      free (last_name);
+      last_name = strdup (pw->pw_name);
+      if (last_name == NULL)
+       {
+         printf ("strdup: %m\n");
+         return 1;
+       }
+      last_uid = pw->pw_uid;
+      ++count;
+    }
+  endpwent ();
+
+  if (count == 0)
+    {
+      printf ("No entries in the password database.\n");
+      return 0;
+    }
+
+  /* Try again, this time interleaving with name-based and UID-based
+     lookup operations.  The counts do not match if the interleaved
+     lookups affected the enumeration.  */
+  size_t new_count = 0;
+  setpwent ();
+  while ((pw  = getpwent ()) != NULL)
+    {
+      if (new_count == count)
+       {
+         printf ("Additional entry in the password database.\n");
+         return 1;
+       }
+      ++new_count;
+      struct passwd *pw2 = getpwnam (first_name);
+      if (pw2 == NULL)
+       {
+         printf ("getpwnam (%s) failed: %m\n", first_name);
+         return 1;
+       }
+      pw2 = getpwnam (last_name);
+      if (pw2 == NULL)
+       {
+         printf ("getpwnam (%s) failed: %m\n", last_name);
+         return 1;
+       }
+      pw2 = getpwuid (first_uid);
+      if (pw2 == NULL)
+       {
+         printf ("getpwuid (%llu) failed: %m\n",
+                 (unsigned long long) first_uid);
+         return 1;
+       }
+      pw2 = getpwuid (last_uid);
+      if (pw2 == NULL)
+       {
+         printf ("getpwuid (%llu) failed: %m\n",
+                 (unsigned long long) last_uid);
+         return 1;
+       }
+    }
+  endpwent ();
+  if (new_count < count)
+    {
+      printf ("Missing entry in the password database.\n");
+      return 1;
+    }
+
+  return 0;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"