time: Improve sanity checking of timekeeping inputs

Unexpected behavior could occur if the time is set to a value large
enough to overflow a 64bit ktime_t (which is something larger then the
year 2262).

Also unexpected behavior could occur if large negative offsets are
injected via adjtimex.

So this patch improves the sanity check timekeeping inputs by
improving the timespec_valid() check, and then makes better use of
timespec_valid() to make sure we don't set the time to an invalid
negative value or one that overflows ktime_t.

Note: This does not protect from setting the time close to overflowing
ktime_t and then letting natural accumulation cause the overflow.

Reported-by: CAI Qian <caiqian@redhat.com>
Reported-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Zhouping Liu <zliu@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1344454580-17031-1-git-send-email-john.stultz@linaro.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 20 insertions, 2 deletions

diff --git a/include/linux/time.h b/include/linux/time.h
index c81c5e40fcb5..b0bbd8f0130d 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -107,11 +107,29 @@ static inline struct timespec timespec_sub(struct timespec lhs,
 	return ts_delta;
 }
 
+#define KTIME_MAX			((s64)~((u64)1 << 63))
+#if (BITS_PER_LONG == 64)
+# define KTIME_SEC_MAX			(KTIME_MAX / NSEC_PER_SEC)
+#else
+# define KTIME_SEC_MAX			LONG_MAX
+#endif
+
 /*
  * Returns true if the timespec is norm, false if denorm:
  */
-#define timespec_valid(ts) \
-	(((ts)->tv_sec >= 0) && (((unsigned long) (ts)->tv_nsec) < NSEC_PER_SEC))
+static inline bool timespec_valid(const struct timespec *ts)
+{
+	/* Dates before 1970 are bogus */
+	if (ts->tv_sec < 0)
+		return false;
+	/* Can't have more nanoseconds then a second */
+	if ((unsigned long)ts->tv_nsec >= NSEC_PER_SEC)
+		return false;
+	/* Disallow values that could overflow ktime_t */
+	if ((unsigned long long)ts->tv_sec >= KTIME_SEC_MAX)
+		return false;
+	return true;
+}
 
 extern void read_persistent_clock(struct timespec *ts);
 extern void read_boot_clock(struct timespec *ts);