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Commit 8ca9d129 authored by Jiri Slaby's avatar Jiri Slaby Committed by Sasha Levin
Browse files

tty: fix up atime/mtime mess, take four 



commit f0bf0bd07943bfde8f5ac39a32664810a379c7d3 upstream.

This problem was taken care of three times already in
* b0de59b5 (TTY: do not update
  atime/mtime on read/write),
* 37b7f3c7 (TTY: fix atime/mtime
  regression), and
* b0b88565 (tty: fix up atime/mtime
  mess, take three)

But it still misses one point. As John Paul correctly points out, we
do not care about setting date. If somebody ever changes wall
time backwards (by mistake for example), tty timestamps are never
updated until the original wall time passes.

So check the absolute difference of times and if it large than "8
seconds or so", always update the time. That means we will update
immediatelly when changing time. Ergo, CAP_SYS_TIME can foul the
check, but it was always that way.

Thanks John for serving me this so nicely debugged.

Signed-off-by: default avatarJiri Slaby <jslaby@suse.cz>
Reported-by: default avatarJohn Paul Perry <john_paul.perry@alcatel-lucent.com>
Acked-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarSasha Levin <sasha.levin@oracle.com>
parent b7dc640d

drivers/tty/tty_io.c

+2 −2
Original line number Diff line number Diff line
@@ -975,8 +975,8 @@ 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() & ~7;

	if ((long)(sec - time->tv_sec) > 0)

	unsigned long sec = get_seconds();

	if (abs(sec - time->tv_sec) & ~7)

		time->tv_sec = sec;

}