The patch titled
Subject: ktime_add_ns() may overflow on 32bit architectures
has been added to the -mm tree. Its filename is
ktime_add_ns-may-overflow-on-32bit-architectures.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: David Engraf <david.engraf@xxxxxxxxx>
Subject: 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 <david.engraf@xxxxxxxxx>
Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/hrtimer.c | 4 ++++
1 file changed, 4 insertions(+)
diff -puN kernel/hrtimer.c~ktime_add_ns-may-overflow-on-32bit-architectures kernel/hrtimer.c
--- a/kernel/hrtimer.c~ktime_add_ns-may-overflow-on-32bit-architectures
+++ a/kernel/hrtimer.c
@@ -275,6 +275,10 @@ ktime_t ktime_add_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);
}
_
Patches currently in -mm which might be from david.engraf@xxxxxxxxx are
ktime_add_ns-may-overflow-on-32bit-architectures.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
