[PATCH 3.16.y-ckt 133/183] ntp: Fixup adjtimex freq validation on 32-bit systems

[Luis Henriques]

3.16.7-ckt8 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: John Stultz <john.stultz at linaro.org>

commit 29183a70b0b828500816bd794b3fe192fce89f73 upstream.

Additional validation of adjtimex freq values to avoid
potential multiplication overflows were added in commit
5e5aeb4367b (time: adjtimex: Validate the ADJ_FREQUENCY values)

Unfortunately the patch used LONG_MAX/MIN instead of
LLONG_MAX/MIN, which was fine on 64-bit systems, but being
much smaller on 32-bit systems caused false positives
resulting in most direct frequency adjustments to fail w/
EINVAL.

ntpd only does direct frequency adjustments at startup, so
the issue was not as easily observed there, but other time
sync applications like ptpd and chrony were more effected by
the bug.

See bugs:

  https://bugzilla.kernel.org/show_bug.cgi?id=92481
  https://bugzilla.redhat.com/show_bug.cgi?id=1188074

This patch changes the checks to use LLONG_MAX for
clarity, and additionally the checks are disabled
on 32-bit systems since LLONG_MAX/PPM_SCALE is always
larger then the 32-bit long freq value, so multiplication
overflows aren't possible there.

Reported-by: Josh Boyer <jwboyer at fedoraproject.org>
Reported-by: George Joseph <george.joseph at fairview5.com>
Tested-by: George Joseph <george.joseph at fairview5.com>
Signed-off-by: John Stultz <john.stultz at linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Sasha Levin <sasha.levin at oracle.com>
Link: http://lkml.kernel.org/r/1423553436-29747-1-git-send-email-john.stultz@linaro.org
[ Prettified the changelog and the comments a bit. ]
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 kernel/time/ntp.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index 3fca3fdd7c82..b1d6d26dbdc3 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -632,10 +632,14 @@ int ntp_validate_timex(struct timex *txc)
 	if ((txc->modes & ADJ_SETOFFSET) && (!capable(CAP_SYS_TIME)))
 		return -EPERM;
 
-	if (txc->modes & ADJ_FREQUENCY) {
-		if (LONG_MIN / PPM_SCALE > txc->freq)
+	/*
+	 * Check for potential multiplication overflows that can
+	 * only happen on 64-bit systems:
+	 */
+	if ((txc->modes & ADJ_FREQUENCY) && (BITS_PER_LONG == 64)) {
+		if (LLONG_MIN / PPM_SCALE > txc->freq)
 			return -EINVAL;
-		if (LONG_MAX / PPM_SCALE < txc->freq)
+		if (LLONG_MAX / PPM_SCALE < txc->freq)
 			return -EINVAL;
 	}