From: David Engraf Date: Tue, 26 Mar 2013 23:24:11 +0000 (+1100) Subject: ktime_add_ns() may overflow on 32bit architectures X-Git-Tag: next-20130404~3^2~480 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=f82576b9d82396bfa2040a9b4fd2f2ae8d7220b5;p=karo-tx-linux.git 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 --- 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); }