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.

Conflicts:
	NEWS

5 files changed, 134 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index 22f201739e..8b13f7b0ca 100644
--- 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.
+
 2015-04-21  Arjun Shankar  <arjun.is@lostca.se>
 
 	[BZ #18287]
diff --git a/NEWS b/NEWS
index 8160427710..8a63fb91ca 100644
--- a/NEWS
+++ b/NEWS
@@ -10,7 +10,7 @@ Version 2.20.1
 * The following bugs are resolved with this release:
 
   16009, 16617, 16618, 17266, 17370, 17371, 17460, 17485, 17555, 17625,
-  17630, 17801, 18287
+  17630, 17801, 18007, 18287.
 
 * A buffer overflow in gethostbyname_r and related functions performing DNS
   requests has been fixed.  If the NSS functions were called with a
@@ -19,6 +19,11 @@ Version 2.20.1
   potentially arbitrary code execution, using crafted, but syntactically
   valid DNS responses.  (CVE-2015-1781)
 
+* 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.
+
 * Added support for TSX lock elision of pthread mutexes on powerpc32, powerpc64
   and powerpc64le.  This may improve lock scaling of existing programs on
   HTM capable systems.  The lock elision code is only enabled with
diff --git a/nss/Makefile b/nss/Makefile
index 1fa7f1f397..d6f0139bf5 100644
--- a/nss/Makefile
+++ b/nss/Makefile
@@ -39,7 +39,7 @@ 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 212b938fdf..cc38174df0 100644
--- 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
index 0000000000..f2e8abce60
--- /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"