glibc/nss/tst-nss-getpwent.c

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/* Copyright (C) 2015-2016 Free Software Foundation, Inc.
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.
2015-04-29 12:41:25 +00:00
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"