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03d2730b44
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❌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❌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.
119 lines
2.8 KiB
C
119 lines
2.8 KiB
C
/* Copyright (C) 2015 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <pwd.h>
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#include <stdbool.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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int
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do_test (void)
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{
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/* Count the number of entries in the password database, and fetch
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data from the first and last entries. */
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size_t count = 0;
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struct passwd * pw;
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char *first_name = NULL;
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uid_t first_uid = 0;
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char *last_name = NULL;
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uid_t last_uid = 0;
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setpwent ();
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while ((pw = getpwent ()) != NULL)
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{
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if (first_name == NULL)
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{
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first_name = strdup (pw->pw_name);
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if (first_name == NULL)
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{
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printf ("strdup: %m\n");
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return 1;
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}
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first_uid = pw->pw_uid;
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}
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free (last_name);
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last_name = strdup (pw->pw_name);
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if (last_name == NULL)
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{
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printf ("strdup: %m\n");
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return 1;
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}
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last_uid = pw->pw_uid;
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++count;
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}
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endpwent ();
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if (count == 0)
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{
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printf ("No entries in the password database.\n");
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return 0;
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}
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/* Try again, this time interleaving with name-based and UID-based
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lookup operations. The counts do not match if the interleaved
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lookups affected the enumeration. */
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size_t new_count = 0;
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setpwent ();
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while ((pw = getpwent ()) != NULL)
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{
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if (new_count == count)
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{
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printf ("Additional entry in the password database.\n");
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return 1;
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}
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++new_count;
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struct passwd *pw2 = getpwnam (first_name);
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if (pw2 == NULL)
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{
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printf ("getpwnam (%s) failed: %m\n", first_name);
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return 1;
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}
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pw2 = getpwnam (last_name);
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if (pw2 == NULL)
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{
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printf ("getpwnam (%s) failed: %m\n", last_name);
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return 1;
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}
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pw2 = getpwuid (first_uid);
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if (pw2 == NULL)
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{
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printf ("getpwuid (%llu) failed: %m\n",
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(unsigned long long) first_uid);
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return 1;
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}
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pw2 = getpwuid (last_uid);
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if (pw2 == NULL)
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{
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printf ("getpwuid (%llu) failed: %m\n",
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(unsigned long long) last_uid);
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return 1;
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}
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}
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endpwent ();
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if (new_count < count)
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{
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printf ("Missing entry in the password database.\n");
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return 1;
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}
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return 0;
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}
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#define TEST_FUNCTION do_test ()
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#include "../test-skeleton.c"
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