| From | Ben Hutchings <> | Date | Fri, 10 May 2013 14:39:41 +0100 | Subject | [022/118] hrtimer: Fix ktime_add_ns() overflow on 32bit architectures |
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3.2.45-rc1 review patch. If anyone has any objections, please let me know.
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From: David Engraf <david.engraf@sysgo.com>
commit 51fd36f3fad8447c487137ae26b9d0b3ce77bb25 upstream.
One can trigger 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 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 fix caps the value to KTIME_MAX.
This error doesn't occurs on 64bit or architectures supporting CONFIG_KTIME_SCALAR (e.g. ARM, x86-32).
Signed-off-by: David Engraf <david.engraf@sysgo.com> [jstultz: Minor tweaks to commit message & header] Signed-off-by: John Stultz <john.stultz@linaro.org> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- kernel/hrtimer.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/kernel/hrtimer.c +++ b/kernel/hrtimer.c @@ -298,6 +298,10 @@ ktime_t ktime_sub_ns(const ktime_t kt, u } 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); }
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