261 lines
7.4 KiB
Diff
261 lines
7.4 KiB
Diff
commit 5a3afa9738f3dbbaf8c0a35665318c1af782111b
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Author: Florian Weimer <fweimer@redhat.com>
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Date: Tue Aug 13 15:53:19 2019 +0200
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login: Replace macro-based control flow with function calls in utmp
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diff --git a/login/utmp_file.c b/login/utmp_file.c
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index da1baa6948d0eb39..812de8fd3d099ce9 100644
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--- a/login/utmp_file.c
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+++ b/login/utmp_file.c
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@@ -52,58 +52,71 @@ static struct utmp last_entry;
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/* Do-nothing handler for locking timeout. */
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static void timeout_handler (int signum) {};
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-/* LOCK_FILE(fd, type) failure_statement
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- attempts to get a lock on the utmp file referenced by FD. If it fails,
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- the failure_statement is executed, otherwise it is skipped.
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- LOCKING_FAILED()
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- jumps into the UNLOCK_FILE macro and ensures cleanup of LOCK_FILE.
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- UNLOCK_FILE(fd)
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- unlocks the utmp file referenced by FD and performs the cleanup of
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- LOCK_FILE.
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- */
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-#define LOCK_FILE(fd, type) \
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-{ \
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- struct flock fl; \
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- struct sigaction action, old_action; \
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- unsigned int old_timeout; \
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- \
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- /* Cancel any existing alarm. */ \
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- old_timeout = alarm (0); \
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- \
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- /* Establish signal handler. */ \
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- action.sa_handler = timeout_handler; \
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- __sigemptyset (&action.sa_mask); \
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- action.sa_flags = 0; \
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- __sigaction (SIGALRM, &action, &old_action); \
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- \
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- alarm (TIMEOUT); \
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- \
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- /* Try to get the lock. */ \
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- memset (&fl, '\0', sizeof (struct flock)); \
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- fl.l_type = (type); \
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- fl.l_whence = SEEK_SET; \
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- if (__fcntl64_nocancel ((fd), F_SETLKW, &fl) < 0)
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-
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-#define LOCKING_FAILED() \
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- goto unalarm_return
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-
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-#define UNLOCK_FILE(fd) \
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- /* Unlock the file. */ \
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- fl.l_type = F_UNLCK; \
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- __fcntl64_nocancel ((fd), F_SETLKW, &fl); \
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- \
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- unalarm_return: \
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- /* Reset the signal handler and alarm. We must reset the alarm \
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- before resetting the handler so our alarm does not generate a \
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- spurious SIGALRM seen by the user. However, we cannot just set \
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- the user's old alarm before restoring the handler, because then \
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- it's possible our handler could catch the user alarm's SIGARLM \
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- and then the user would never see the signal he expected. */ \
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- alarm (0); \
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- __sigaction (SIGALRM, &old_action, NULL); \
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- if (old_timeout != 0) \
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- alarm (old_timeout); \
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-} while (0)
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+
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+/* try_file_lock (LOCKING, FD, TYPE) returns true if the locking
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+ operation failed and recovery needs to be performed.
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+ (file_lock_restore (LOCKING) still needs to be called.)
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+
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+ file_unlock (FD) removes the lock (which must have been
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+ acquired).
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+
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+ file_lock_restore (LOCKING) is needed to clean up in both
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+ cases. */
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+
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+struct file_locking
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+{
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+ struct sigaction old_action;
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+ unsigned int old_timeout;
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+};
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+
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+static bool
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+try_file_lock (struct file_locking *locking, int fd, int type)
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+{
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+ /* Cancel any existing alarm. */
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+ locking->old_timeout = alarm (0);
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+
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+ /* Establish signal handler. */
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+ struct sigaction action;
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+ action.sa_handler = timeout_handler;
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+ __sigemptyset (&action.sa_mask);
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+ action.sa_flags = 0;
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+ __sigaction (SIGALRM, &action, &locking->old_action);
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+
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+ alarm (TIMEOUT);
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+
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+ /* Try to get the lock. */
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+ struct flock fl =
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+ {
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+ .l_type = type,
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+ fl.l_whence = SEEK_SET,
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+ };
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+ return __fcntl64_nocancel (fd, F_SETLKW, &fl) < 0;
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+}
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+
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+static void
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+file_unlock (int fd)
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+{
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+ struct flock fl =
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+ {
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+ .l_type = F_UNLCK,
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+ };
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+ __fcntl64_nocancel (fd, F_SETLKW, &fl);
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+}
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+
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+static void
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+file_lock_restore (struct file_locking *locking)
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+{
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+ /* Reset the signal handler and alarm. We must reset the alarm
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+ before resetting the handler so our alarm does not generate a
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+ spurious SIGALRM seen by the user. However, we cannot just set
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+ the user's old alarm before restoring the handler, because then
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+ it's possible our handler could catch the user alarm's SIGARLM
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+ and then the user would never see the signal he expected. */
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+ alarm (0);
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+ __sigaction (SIGALRM, &locking->old_action, NULL);
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+ if (locking->old_timeout != 0)
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+ alarm (locking->old_timeout);
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+}
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#ifndef TRANSFORM_UTMP_FILE_NAME
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# define TRANSFORM_UTMP_FILE_NAME(file_name) (file_name)
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@@ -153,16 +166,16 @@ __libc_getutent_r (struct utmp *buffer, struct utmp **result)
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return -1;
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}
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- LOCK_FILE (file_fd, F_RDLCK)
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+ struct file_locking fl;
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+ if (try_file_lock (&fl, file_fd, F_RDLCK))
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+ nbytes = 0;
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+ else
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{
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- nbytes = 0;
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- LOCKING_FAILED ();
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+ /* Read the next entry. */
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+ nbytes = __read_nocancel (file_fd, &last_entry, sizeof (struct utmp));
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+ file_unlock (file_fd);
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}
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-
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- /* Read the next entry. */
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- nbytes = __read_nocancel (file_fd, &last_entry, sizeof (struct utmp));
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-
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- UNLOCK_FILE (file_fd);
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+ file_lock_restore (&fl);
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if (nbytes != sizeof (struct utmp))
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{
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@@ -188,10 +201,12 @@ internal_getut_r (const struct utmp *id, struct utmp *buffer,
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{
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int result = -1;
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- LOCK_FILE (file_fd, F_RDLCK)
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+ struct file_locking fl;
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+ if (try_file_lock (&fl, file_fd, F_RDLCK))
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{
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*lock_failed = true;
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- LOCKING_FAILED ();
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+ file_lock_restore (&fl);
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+ return -1;
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}
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if (id->ut_type == RUN_LVL || id->ut_type == BOOT_TIME
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@@ -241,7 +256,8 @@ internal_getut_r (const struct utmp *id, struct utmp *buffer,
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result = 0;
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unlock_return:
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- UNLOCK_FILE (file_fd);
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+ file_unlock (file_fd);
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+ file_lock_restore (&fl);
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return result;
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}
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@@ -287,10 +303,12 @@ __libc_getutline_r (const struct utmp *line, struct utmp *buffer,
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return -1;
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}
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- LOCK_FILE (file_fd, F_RDLCK)
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+ struct file_locking fl;
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+ if (try_file_lock (&fl, file_fd, F_RDLCK))
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{
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*result = NULL;
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- LOCKING_FAILED ();
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+ file_lock_restore (&fl);
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+ return -1;
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}
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while (1)
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@@ -318,7 +336,8 @@ __libc_getutline_r (const struct utmp *line, struct utmp *buffer,
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*result = buffer;
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unlock_return:
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- UNLOCK_FILE (file_fd);
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+ file_unlock (file_fd);
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+ file_lock_restore (&fl);
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return ((*result == NULL) ? -1 : 0);
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}
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@@ -375,10 +394,11 @@ __libc_pututline (const struct utmp *data)
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}
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}
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- LOCK_FILE (file_fd, F_WRLCK)
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+ struct file_locking fl;
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+ if (try_file_lock (&fl, file_fd, F_WRLCK))
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{
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- pbuf = NULL;
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- LOCKING_FAILED ();
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+ file_lock_restore (&fl);
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+ return NULL;
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}
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if (found < 0)
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@@ -421,7 +441,8 @@ __libc_pututline (const struct utmp *data)
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}
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unlock_return:
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- UNLOCK_FILE (file_fd);
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+ file_unlock (file_fd);
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+ file_lock_restore (&fl);
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return pbuf;
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}
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@@ -450,8 +471,13 @@ __libc_updwtmp (const char *file, const struct utmp *utmp)
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if (fd < 0)
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return -1;
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- LOCK_FILE (fd, F_WRLCK)
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- LOCKING_FAILED ();
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+ struct file_locking fl;
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+ if (try_file_lock (&fl, fd, F_WRLCK))
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+ {
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+ file_lock_restore (&fl);
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+ __close_nocancel_nostatus (fd);
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+ return -1;
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+ }
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/* Remember original size of log file. */
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offset = __lseek64 (fd, 0, SEEK_END);
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@@ -477,7 +503,8 @@ __libc_updwtmp (const char *file, const struct utmp *utmp)
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result = 0;
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unlock_return:
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- UNLOCK_FILE (fd);
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+ file_unlock (file_fd);
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+ file_lock_restore (&fl);
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/* Close WTMP file. */
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__close_nocancel_nostatus (fd);
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