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>

5 files changed, 29 insertions, 22 deletions

diff --git a/include/linux/ktime.h b/include/linux/ktime.h
index 36c542b70c6d..2cd7fa73d1af 100644
--- a/include/linux/ktime.h
+++ b/include/linux/ktime.h
@@ -310,6 +310,8 @@ static inline ktime_t ktime_sub_us(const ktime_t kt, const u64 usec)
         return ktime_sub_ns(kt, usec * 1000);
 }
 
+extern ktime_t ktime_add_safe(const ktime_t lhs, const ktime_t rhs);
+
 /*
  * The resolution of the clocks. The resolution value is returned in
  * the clock_getres() system call to give application programmers an
diff --git a/kernel/futex.c b/kernel/futex.c
index a6baaec44b8f..221f2128a437 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2116,7 +2116,7 @@ asmlinkage long sys_futex(u32 __user *uaddr, int op, u32 val,
 
                 t = timespec_to_ktime(ts);
                 if (cmd == FUTEX_WAIT)
-                        t = ktime_add(ktime_get(), t);
+                        t = ktime_add_safe(ktime_get(), t);
                 tp = &t;
         }
         /*
diff --git a/kernel/futex_compat.c b/kernel/futex_compat.c
index 133d558db452..7d5e4b016f39 100644
--- a/kernel/futex_compat.c
+++ b/kernel/futex_compat.c
@@ -176,7 +176,7 @@ asmlinkage long compat_sys_futex(u32 __user *uaddr, int op, u32 val,
 
                 t = timespec_to_ktime(ts);
                 if (cmd == FUTEX_WAIT)
-                        t = ktime_add(ktime_get(), t);
+                        t = ktime_add_safe(ktime_get(), t);
                 tp = &t;
         }
         if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE)
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;
 
diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
index 022c9c3cee6f..a9b04203a66d 100644
--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -767,9 +767,11 @@ common_timer_set(struct k_itimer *timr, int flags,
         /* SIGEV_NONE timers are not queued ! See common_timer_get */
         if (((timr->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE)) {
                 /* Setup correct expiry time for relative timers */
-                if (mode == HRTIMER_MODE_REL)
-                        timer->expires = ktime_add(timer->expires,
-                                                   timer->base->get_time());
+                if (mode == HRTIMER_MODE_REL) {
+                        timer->expires =
+                                ktime_add_safe(timer->expires,
+                                               timer->base->get_time());
+                }
                 return 0;
         }