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login: Disarm timer after utmp lock acquisition [BZ #24879] 

If the file processing takes a long time for some reason, SIGALRM can
arrive while the file is still being processed.  At that point, file
access will fail with EINTR.  Disarming the timer after lock
acquisition avoids that.  (If there was a previous alarm, it is the
responsibility of the caller to deal with the EINTR error.)
fw/bug25112
Florian Weimer 7 years ago
parent
17e1347452
commit
628598be7e
2 changed files with 41 additions and 52 deletions
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  1. 13
      ChangeLog
  2. 80
      login/utmp_file.c

13
ChangeLog
View File

@ -1,3 +1,16 @@
2019-08-15 Florian Weimer <fweimer@redhat.com>
[BZ #24879]
login: Disarm timer after utmp lock acquisition.
* login/utmp_file.c (struct file_locking): Remove.
(try_file_lock): Adjust.
(file_lock_restore): Remove function.
(__libc_getutent_r): .
(internal_getut_r): Likewise.
(__libc_getutline_r): Likewise.
(__libc_pututline): Likewise.
(__libc_updwtmp): Likewise.
2019-08-15 Florian Weimer <fweimer@redhat.com>
nptl: Remove pthread_self compatibility symbol from libpthread.

80
login/utmp_file.c
View File

@ -55,32 +55,23 @@ static void timeout_handler (int signum) {};
/* try_file_lock (LOCKING, FD, TYPE) returns true if the locking
operation failed and recovery needs to be performed.
(file_lock_restore (LOCKING) still needs to be called.)
file_unlock (FD) removes the lock (which must have been
acquired).
file_lock_restore (LOCKING) is needed to clean up in both
cases. */
struct file_locking
{
struct sigaction old_action;
unsigned int old_timeout;
};
successfully acquired). */
static bool
try_file_lock (struct file_locking *locking, int fd, int type)
try_file_lock (int fd, int type)
{
/* Cancel any existing alarm. */
locking->old_timeout = alarm (0);
int old_timeout = alarm (0);
/* Establish signal handler. */
struct sigaction old_action;
struct sigaction action;
action.sa_handler = timeout_handler;
__sigemptyset (&action.sa_mask);
action.sa_flags = 0;
__sigaction (SIGALRM, &action, &locking->old_action);
__sigaction (SIGALRM, &action, &old_action);
alarm (TIMEOUT);
@ -90,7 +81,23 @@ try_file_lock (struct file_locking *locking, int fd, int type)
.l_type = type,
fl.l_whence = SEEK_SET,
};
return __fcntl64_nocancel (fd, F_SETLKW, &fl) < 0;
bool status = __fcntl64_nocancel (fd, F_SETLKW, &fl) < 0;
int saved_errno = errno;
/* Reset the signal handler and alarm. We must reset the alarm
before resetting the handler so our alarm does not generate a
spurious SIGALRM seen by the user. However, we cannot just set
the user's old alarm before restoring the handler, because then
it's possible our handler could catch the user alarm's SIGARLM and
then the user would never see the signal he expected. */
alarm (0);
__sigaction (SIGALRM, &old_action, NULL);
if (old_timeout != 0)
alarm (old_timeout);
__set_errno (saved_errno);
return status;
}
static void
@ -103,21 +110,6 @@ file_unlock (int fd)
__fcntl64_nocancel (fd, F_SETLKW, &fl);
}
static void
file_lock_restore (struct file_locking *locking)
{
/* Reset the signal handler and alarm. We must reset the alarm
before resetting the handler so our alarm does not generate a
spurious SIGALRM seen by the user. However, we cannot just set
the user's old alarm before restoring the handler, because then
it's possible our handler could catch the user alarm's SIGARLM
and then the user would never see the signal he expected. */
alarm (0);
__sigaction (SIGALRM, &locking->old_action, NULL);
if (locking->old_timeout != 0)
alarm (locking->old_timeout);
}
#ifndef TRANSFORM_UTMP_FILE_NAME
# define TRANSFORM_UTMP_FILE_NAME(file_name) (file_name)
#endif
@ -166,8 +158,7 @@ __libc_getutent_r (struct utmp *buffer, struct utmp **result)
return -1;
}
struct file_locking fl;
if (try_file_lock (&fl, file_fd, F_RDLCK))
if (try_file_lock (file_fd, F_RDLCK))
nbytes = 0;
else
{
@ -175,7 +166,6 @@ __libc_getutent_r (struct utmp *buffer, struct utmp **result)
nbytes = __read_nocancel (file_fd, &last_entry, sizeof (struct utmp));
file_unlock (file_fd);
}
file_lock_restore (&fl);
if (nbytes != sizeof (struct utmp))
{
@ -201,11 +191,9 @@ internal_getut_r (const struct utmp *id, struct utmp *buffer,
{
int result = -1;
struct file_locking fl;
if (try_file_lock (&fl, file_fd, F_RDLCK))
if (try_file_lock (file_fd, F_RDLCK))
{
*lock_failed = true;
file_lock_restore (&fl);
return -1;
}
@ -257,7 +245,6 @@ internal_getut_r (const struct utmp *id, struct utmp *buffer,
unlock_return:
file_unlock (file_fd);
file_lock_restore (&fl);
return result;
}
@ -303,11 +290,9 @@ __libc_getutline_r (const struct utmp *line, struct utmp *buffer,
return -1;
}
struct file_locking fl;
if (try_file_lock (&fl, file_fd, F_RDLCK))
if (try_file_lock (file_fd, F_RDLCK))
{
*result = NULL;
file_lock_restore (&fl);
return -1;
}
@ -337,7 +322,6 @@ __libc_getutline_r (const struct utmp *line, struct utmp *buffer,
unlock_return:
file_unlock (file_fd);
file_lock_restore (&fl);
return ((*result == NULL) ? -1 : 0);
}
@ -394,12 +378,8 @@ __libc_pututline (const struct utmp *data)
}
}
struct file_locking fl;
if (try_file_lock (&fl, file_fd, F_WRLCK))
{
file_lock_restore (&fl);
return NULL;
}
if (try_file_lock (file_fd, F_WRLCK))
return NULL;
if (found < 0)
{
@ -442,7 +422,6 @@ __libc_pututline (const struct utmp *data)
unlock_return:
file_unlock (file_fd);
file_lock_restore (&fl);
return pbuf;
}
@ -471,10 +450,8 @@ __libc_updwtmp (const char *file, const struct utmp *utmp)
if (fd < 0)
return -1;
struct file_locking fl;
if (try_file_lock (&fl, fd, F_WRLCK))
if (try_file_lock (fd, F_WRLCK))
{
file_lock_restore (&fl);
__close_nocancel_nostatus (fd);
return -1;
}
@ -504,7 +481,6 @@ __libc_updwtmp (const char *file, const struct utmp *utmp)
unlock_return:
file_unlock (fd);
file_lock_restore (&fl);
/* Close WTMP file. */
__close_nocancel_nostatus (fd);

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