hrtimer: check relative timeouts for overflow

Various user space callers ask for relative timeouts. While we fixed
that overflow issue in hrtimer_start(), the sites which convert
relative user space values to absolute timeouts themself were uncovered.

Instead of putting overflow checks into each place add a function
which does the sanity checking and convert all affected callers to use
it.

Thanks to Frans Pop, who reported the problem and tested the fixes.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Tested-by: Frans Pop <elendil@planet.nl>

1 files changed, 20 insertions, 17 deletions

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 3f4a57c7895d..c2893af9479e 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -326,6 +326,23 @@ u64 ktime_divns(const ktime_t kt, s64 div)
 #endif /* BITS_PER_LONG >= 64 */
 
 /*
+ * Add two ktime values and do a safety check for overflow:
+ */
+ktime_t ktime_add_safe(const ktime_t lhs, const ktime_t rhs)
+{
+        ktime_t res = ktime_add(lhs, rhs);
+
+        /*
+         * We use KTIME_SEC_MAX here, the maximum timeout which we can
+         * return to user space in a timespec:
+         */
+        if (res.tv64 < 0 || res.tv64 < lhs.tv64 || res.tv64 < rhs.tv64)
+                res = ktime_set(KTIME_SEC_MAX, 0);
+
+        return res;
+}
+
+/*
  * Check, whether the timer is on the callback pending list
  */
 static inline int hrtimer_cb_pending(const struct hrtimer *timer)
@@ -682,13 +699,7 @@ u64 hrtimer_forward(struct hrtimer *timer, ktime_t now, ktime_t interval)
                  */
                 orun++;
         }
-        timer->expires = ktime_add(timer->expires, interval);
-        /*
-         * Make sure, that the result did not wrap with a very large
-         * interval.
-         */
-        if (timer->expires.tv64 < 0)
-                timer->expires = ktime_set(KTIME_SEC_MAX, 0);
+        timer->expires = ktime_add_safe(timer->expires, interval);
 
         return orun;
 }
@@ -839,7 +850,7 @@ hrtimer_start(struct hrtimer *timer, ktime_t tim, const enum hrtimer_mode mode)
         new_base = switch_hrtimer_base(timer, base);
 
         if (mode == HRTIMER_MODE_REL) {
-                tim = ktime_add(tim, new_base->get_time());
+                tim = ktime_add_safe(tim, new_base->get_time());
                 /*
                  * CONFIG_TIME_LOW_RES is a temporary way for architectures
                  * to signal that they simply return xtime in
@@ -848,16 +859,8 @@ hrtimer_start(struct hrtimer *timer, ktime_t tim, const enum hrtimer_mode mode)
                  * timeouts. This will go away with the GTOD framework.
                  */
 #ifdef CONFIG_TIME_LOW_RES
-                tim = ktime_add(tim, base->resolution);
+                tim = ktime_add_safe(tim, base->resolution);
 #endif
-                /*
-                 * Careful here: User space might have asked for a
-                 * very long sleep, so the add above might result in a
-                 * negative number, which enqueues the timer in front
-                 * of the queue.
-                 */
-                if (tim.tv64 < 0)
-                        tim.tv64 = KTIME_MAX;
         }
         timer->expires = tim;