From 4a4910c0e35a91e49983061f04122082775629f2 Mon Sep 17 00:00:00 2001 From: David Engraf Date: Wed, 27 Mar 2013 10:24:11 +1100 Subject: [PATCH] ktime_add_ns() may overflow on 32bit architectures I've triggered an overflow when using ktime_add_ns() on a 32bit architecture not supporting CONFIG_KTIME_SCALAR. When passing a very high value for u64 nsec, e.g. 7881299347898368000 the do_div() function converts this value to seconds (7881299347) which is still to high to pass to the ktime_set() function as long. The result in my case is a negative value. The problem on my system occurs in the tick-sched.c, tick_nohz_stop_sched_tick() when time_delta is set to timekeeping_max_deferment(). The check for time_delta < KTIME_MAX is valid, thus ktime_add_ns() is called with a too large value resulting in a negative expire value. This leads to an endless loop in the ticker code: time_delta: 7881299347898368000 expires = ktime_add_ns(last_update, time_delta) expires: negative value This error doesn't occurs on 64bit or architectures supporting CONFIG_KTIME_SCALAR (e.g. ARM, x86-32). 64-bit arches doesn't run into this problem because ktime_add_ns() can directly calculate the result without calling do_div() and ktime_set(). Signed-off-by: David Engraf Cc: Eric Dumazet Cc: Thomas Gleixner Cc: John Stultz Signed-off-by: Andrew Morton --- kernel/hrtimer.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c index cc47812d3feb..320a7aae32e7 100644 --- a/kernel/hrtimer.c +++ b/kernel/hrtimer.c @@ -275,6 +275,10 @@ ktime_t ktime_add_ns(const ktime_t kt, u64 nsec) } else { unsigned long rem = do_div(nsec, NSEC_PER_SEC); + /* Make sure nsec fits into long */ + if (unlikely(nsec > KTIME_SEC_MAX)) + return (ktime_t){ .tv64 = KTIME_MAX }; + tmp = ktime_set((long)nsec, rem); } -- 2.39.5