login: pututxline could fail to overwrite existing entries [BZ #24902]
The internal_getut_r function updates the file_offset variable and therefore must always update last_entry as well. Previously, if pututxline could not upgrade the read lock to a write lock, internal_getut_r would update file_offset only, without updating last_entry, and a subsequent call would not overwrite the existing utmpx entry at file_offset, instead creating a new entry. This has been observed to cause unbounded file growth in high-load situations. This commit removes the buffer argument to internal_getut_r and updates the last_entry variable directly, along with file_offset. Initially reported and fixed by Ondřej Lysoněk. Reviewed-by: Gabriel F. T. Gomes <gabrielftg@linux.ibm.com>
This commit is contained in:
Florian Weimer
parent
3a9d025fdd
commit
61d3db4281
10
ChangeLog
10
ChangeLog
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@ -1,3 +1,13 @@
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2019-08-28 Florian Weimer <fweimer@redhat.com>
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[BZ #24902]
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* login/Makefile (tests): Add tst-pututxline-lockfail.
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(tst-pututxline-lockfail): Link with -lpthread.
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* login/utmp_file.c (internal_getut_r): Remove buffer argument.
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(__libc_getutid_r): Adjust.
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(__libc_pututline): Likewise. Check for file_offset == -1.
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* login/tst-pututxline-lockfail.c: New file.
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2019-08-28 Stefan Liebler <stli@linux.ibm.com>
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* posix/tst-regex.c (do_test): Use tst-regex.input as input file.
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@ -43,7 +43,8 @@ endif
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subdir-dirs = programs
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vpath %.c programs
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tests := tst-utmp tst-utmpx tst-grantpt tst-ptsname tst-getlogin tst-updwtmpx
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tests := tst-utmp tst-utmpx tst-grantpt tst-ptsname tst-getlogin tst-updwtmpx \
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tst-pututxline-lockfail
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# Build the -lutil library with these extra functions.
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extra-libs := libutil
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@ -71,3 +72,5 @@ endif
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$(inst_libexecdir)/pt_chown: $(objpfx)pt_chown $(+force)
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$(make-target-directory)
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-$(INSTALL_PROGRAM) -m 4755 -o root $< $@
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$(objpfx)tst-pututxline-lockfail: $(shared-thread-library)
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@ -0,0 +1,176 @@
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/* Test the lock upgrade path in tst-pututxline.
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Copyright (C) 2019 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 License as
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published by the Free Software Foundation; either version 2.1 of the
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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; see the file COPYING.LIB. If
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not, see <http://www.gnu.org/licenses/>. */
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/* pututxline upgrades the read lock on the file to a write lock.
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This test verifies that if the lock upgrade fails, the utmp
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subsystem remains in a consistent state, so that pututxline can be
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called again. */
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#include <errno.h>
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#include <fcntl.h>
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#include <stdlib.h>
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#include <support/check.h>
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#include <support/namespace.h>
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#include <support/support.h>
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#include <support/temp_file.h>
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#include <support/xthread.h>
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#include <support/xunistd.h>
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#include <unistd.h>
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#include <utmp.h>
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#include <utmpx.h>
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/* Path to the temporary utmp file. */
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static char *path;
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/* Used to synchronize the subprocesses. The barrier itself is
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allocated in shared memory. */
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static pthread_barrier_t *barrier;
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/* Use pututxline to write an entry for PID. */
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static struct utmpx *
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write_entry (pid_t pid)
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{
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struct utmpx ut =
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{
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.ut_type = LOGIN_PROCESS,
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.ut_id = "1",
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.ut_user = "root",
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.ut_pid = pid,
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.ut_line = "entry",
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.ut_host = "localhost",
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};
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return pututxline (&ut);
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}
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/* Create the initial entry in a subprocess, so that the utmp
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subsystem in the original process is not disturbed. */
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static void
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subprocess_create_entry (void *closure)
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{
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TEST_COMPARE (utmpname (path), 0);
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TEST_VERIFY (write_entry (101) != NULL);
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}
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/* Acquire an advisory read lock on PATH. */
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__attribute__ ((noreturn)) static void
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subprocess_lock_file (void)
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{
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int fd = xopen (path, O_RDONLY, 0);
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struct flock64 fl =
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{
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.l_type = F_RDLCK,
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fl.l_whence = SEEK_SET,
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};
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TEST_COMPARE (fcntl64 (fd, F_SETLKW, &fl), 0);
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/* Signal to the main process that the lock has been acquired. */
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xpthread_barrier_wait (barrier);
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/* Wait for the unlock request from the main process. */
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xpthread_barrier_wait (barrier);
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/* Implicitly unlock the file. */
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xclose (fd);
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/* Overwrite the existing entry. */
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TEST_COMPARE (utmpname (path), 0);
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errno = 0;
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setutxent ();
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TEST_COMPARE (errno, 0);
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TEST_VERIFY (write_entry (102) != NULL);
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errno = 0;
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endutxent ();
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TEST_COMPARE (errno, 0);
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_exit (0);
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}
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static int
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do_test (void)
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{
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xclose (create_temp_file ("tst-pututxline-lockfail-", &path));
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{
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pthread_barrierattr_t attr;
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xpthread_barrierattr_init (&attr);
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xpthread_barrierattr_setpshared (&attr, PTHREAD_SCOPE_PROCESS);
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barrier = support_shared_allocate (sizeof (*barrier));
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xpthread_barrier_init (barrier, &attr, 2);
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xpthread_barrierattr_destroy (&attr);
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}
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/* Write the initial entry. */
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support_isolate_in_subprocess (subprocess_create_entry, NULL);
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pid_t locker_pid = xfork ();
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if (locker_pid == 0)
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subprocess_lock_file ();
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/* Wait for the file locking to complete. */
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xpthread_barrier_wait (barrier);
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/* Try to add another entry. This attempt will fail, with EINTR or
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EAGAIN. */
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TEST_COMPARE (utmpname (path), 0);
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TEST_VERIFY (write_entry (102) == NULL);
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if (errno != EINTR)
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TEST_COMPARE (errno, EAGAIN);
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/* Signal the subprocess to overwrite the entry. */
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xpthread_barrier_wait (barrier);
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/* Wait for write and unlock to complete. */
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{
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int status;
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xwaitpid (locker_pid, &status, 0);
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TEST_COMPARE (status, 0);
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}
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/* The file is no longer locked, so this operation will succeed. */
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TEST_VERIFY (write_entry (103) != NULL);
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errno = 0;
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endutxent ();
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TEST_COMPARE (errno, 0);
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/* Check that there is just one entry with the expected contents.
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If pututxline becomes desynchronized internally, the entry is not
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overwritten (bug 24902). */
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errno = 0;
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setutxent ();
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TEST_COMPARE (errno, 0);
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struct utmpx *ut = getutxent ();
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TEST_VERIFY_EXIT (ut != NULL);
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TEST_COMPARE (ut->ut_type, LOGIN_PROCESS);
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TEST_COMPARE_STRING (ut->ut_id, "1");
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TEST_COMPARE_STRING (ut->ut_user, "root");
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TEST_COMPARE (ut->ut_pid, 103);
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TEST_COMPARE_STRING (ut->ut_line, "entry");
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TEST_COMPARE_STRING (ut->ut_host, "localhost");
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TEST_VERIFY (getutxent () == NULL);
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errno = 0;
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endutxent ();
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TEST_COMPARE (errno, 0);
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xpthread_barrier_destroy (barrier);
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support_shared_free (barrier);
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free (path);
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return 0;
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}
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#include <support/test-driver.c>
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@ -185,9 +185,11 @@ __libc_getutent_r (struct utmp *buffer, struct utmp **result)
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}
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/* Search for *ID, updating last_entry and file_offset. Return 0 on
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success and -1 on failure. If the locking operation failed, write
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true to *LOCK_FAILED. */
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static int
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internal_getut_r (const struct utmp *id, struct utmp *buffer,
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bool *lock_failed)
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internal_getut_r (const struct utmp *id, bool *lock_failed)
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{
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int result = -1;
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@ -206,7 +208,7 @@ internal_getut_r (const struct utmp *id, struct utmp *buffer,
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while (1)
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{
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/* Read the next entry. */
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if (__read_nocancel (file_fd, buffer, sizeof (struct utmp))
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if (__read_nocancel (file_fd, &last_entry, sizeof (struct utmp))
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!= sizeof (struct utmp))
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{
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__set_errno (ESRCH);
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@ -215,7 +217,7 @@ internal_getut_r (const struct utmp *id, struct utmp *buffer,
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}
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file_offset += sizeof (struct utmp);
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if (id->ut_type == buffer->ut_type)
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if (id->ut_type == last_entry.ut_type)
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break;
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}
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}
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@ -227,7 +229,7 @@ internal_getut_r (const struct utmp *id, struct utmp *buffer,
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while (1)
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{
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/* Read the next entry. */
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if (__read_nocancel (file_fd, buffer, sizeof (struct utmp))
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if (__read_nocancel (file_fd, &last_entry, sizeof (struct utmp))
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!= sizeof (struct utmp))
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{
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__set_errno (ESRCH);
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@ -236,7 +238,7 @@ internal_getut_r (const struct utmp *id, struct utmp *buffer,
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}
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file_offset += sizeof (struct utmp);
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if (__utmp_equal (buffer, id))
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if (__utmp_equal (&last_entry, id))
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break;
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}
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}
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@ -265,7 +267,7 @@ __libc_getutid_r (const struct utmp *id, struct utmp *buffer,
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/* We don't have to distinguish whether we can lock the file or
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whether there is no entry. */
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bool lock_failed = false;
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if (internal_getut_r (id, &last_entry, &lock_failed) < 0)
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if (internal_getut_r (id, &lock_failed) < 0)
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{
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*result = NULL;
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return -1;
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@ -330,10 +332,9 @@ unlock_return:
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struct utmp *
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__libc_pututline (const struct utmp *data)
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{
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if (!maybe_setutent ())
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if (!maybe_setutent () || file_offset == -1l)
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return NULL;
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struct utmp buffer;
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struct utmp *pbuf;
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int found;
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@ -369,7 +370,7 @@ __libc_pututline (const struct utmp *data)
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else
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{
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bool lock_failed = false;
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found = internal_getut_r (data, &buffer, &lock_failed);
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found = internal_getut_r (data, &lock_failed);
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if (__builtin_expect (lock_failed, false))
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{
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