tty: clean up the tty time logic a bit
We only care if anything other than the lower 3 bits of the tty has
changed, so just check that way, which makes it a bit faster, and more
obvious what is going on. Also, document this for future developers to
understand why we did this.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 3949d95..e569546 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1025,11 +1025,17 @@
}
EXPORT_SYMBOL(start_tty);
-/* We limit tty time update visibility to every 8 seconds or so. */
static void tty_update_time(struct timespec *time)
{
unsigned long sec = get_seconds();
- if (abs(sec - time->tv_sec) & ~7)
+
+ /*
+ * We only care if the two values differ in anything other than the
+ * lower three bits (i.e every 8 seconds). If so, then we can update
+ * the time of the tty device, otherwise it could be construded as a
+ * security leak to let userspace know the exact timing of the tty.
+ */
+ if ((sec ^ time->tv_sec) & ~7)
time->tv_sec = sec;
}