hrtimers: avoid overflow for large relative timeouts (CVE-2007-5966)

patch 62f0f61e6673e67151a7c8c0f9a09c7ea43fe2b5 in mainline

Relative hrtimers with a large timeout value might end up as negative
timer values, when the current time is added in hrtimer_start().

This in turn is causing the clockevents_set_next() function to set an
huge timeout and sleep for quite a long time when we have a clock
source which is capable of long sleeps like HPET. With PIT this almost
goes unnoticed as the maximum delta is ~27ms. The non-hrt/nohz code
sorts this out in the next timer interrupt, so we never noticed that
problem which has been there since the first day of hrtimers.

This bug became more apparent in 2.6.24 which activates HPET on more
hardware.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 23c03f43e1962d6f0dfa4cb8a716080cf671a48c..355e867f4a3e82066dfdbe79ae4a94d75a311052 100644 (file)
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -825,6 +825,14 @@ hrtimer_start(struct hrtimer *timer, ktime_t tim, const enum hrtimer_mode mode)
 #ifdef CONFIG_TIME_LOW_RES
                tim = ktime_add(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;