This is a note to let you know that I've just added the patch titled

time: Avoid undefined behaviour in ktime_add_safe()

to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: time-avoid-undefined-behaviour-in-ktime_add_safe.patch and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 979515c5645830465739254abc1b1648ada41518 Mon Sep 17 00:00:00 2001

From: Vegard Nossum vegard.nossum@oracle.com Date: Sat, 13 Aug 2016 01:37:04 +0200 Subject: time: Avoid undefined behaviour in ktime_add_safe()

From: Vegard Nossum vegard.nossum@oracle.com

commit 979515c5645830465739254abc1b1648ada41518 upstream.

I ran into this:

================================================================================ UBSAN: Undefined behaviour in kernel/time/hrtimer.c:310:16 signed integer overflow: 9223372036854775807 + 50000 cannot be represented in type 'long long int' CPU: 2 PID: 4798 Comm: trinity-c2 Not tainted 4.8.0-rc1+ #91 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.3-0-ge2fc41e-prebuilt.qemu-project.org 04/01/2014 0000000000000000 ffff88010ce6fb88 ffffffff82344740 0000000041b58ab3 ffffffff84f97a20 ffffffff82344694 ffff88010ce6fbb0 ffff88010ce6fb60 000000000000c350 ffff88010ce6f968 dffffc0000000000 ffffffff857bc320 Call Trace: [<ffffffff82344740>] dump_stack+0xac/0xfc [<ffffffff82344694>] ? _atomic_dec_and_lock+0xc4/0xc4 [<ffffffff8242df78>] ubsan_epilogue+0xd/0x8a [<ffffffff8242e6b4>] handle_overflow+0x202/0x23d [<ffffffff8242e4b2>] ? val_to_string.constprop.6+0x11e/0x11e [<ffffffff8236df71>] ? timerqueue_add+0x151/0x410 [<ffffffff81485c48>] ? hrtimer_start_range_ns+0x3b8/0x1380 [<ffffffff81795631>] ? memset+0x31/0x40 [<ffffffff8242e6fd>] __ubsan_handle_add_overflow+0xe/0x10 [<ffffffff81488ac9>] hrtimer_nanosleep+0x5d9/0x790 [<ffffffff814884f0>] ? hrtimer_init_sleeper+0x80/0x80 [<ffffffff813a9ffb>] ? __might_sleep+0x5b/0x260 [<ffffffff8148be10>] common_nsleep+0x20/0x30 [<ffffffff814906c7>] SyS_clock_nanosleep+0x197/0x210 [<ffffffff81490530>] ? SyS_clock_getres+0x150/0x150 [<ffffffff823c7113>] ? __this_cpu_preempt_check+0x13/0x20 [<ffffffff8162ef60>] ? __context_tracking_exit.part.3+0x30/0x1b0 [<ffffffff81490530>] ? SyS_clock_getres+0x150/0x150 [<ffffffff81007bd3>] do_syscall_64+0x1b3/0x4b0 [<ffffffff845f85aa>] entry_SYSCALL64_slow_path+0x25/0x25 ================================================================================

Add a new ktime_add_unsafe() helper which doesn't check for overflow, but doesn't throw a UBSAN warning when it does overflow either.

Cc: Thomas Gleixner tglx@linutronix.de Cc: Ingo Molnar mingo@kernel.org Cc: Richard Cochran richardcochran@gmail.com Cc: Prarit Bhargava prarit@redhat.com Signed-off-by: Vegard Nossum vegard.nossum@oracle.com Signed-off-by: John Stultz john.stultz@linaro.org Signed-off-by: Jiri Slaby jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- include/linux/ktime.h | 7 +++++++ kernel/time/hrtimer.c | 2 +- 2 files changed, 8 insertions(+), 1 deletion(-)

--- a/include/linux/ktime.h +++ b/include/linux/ktime.h @@ -64,6 +64,13 @@ static inline ktime_t ktime_set(const s6 ({ (ktime_t){ .tv64 = (lhs).tv64 + (rhs).tv64 }; })

/* + * Same as ktime_add(), but avoids undefined behaviour on overflow; however, + * this means that you must check the result for overflow yourself. + */ +#define ktime_add_unsafe(lhs, rhs) \ + ({ (ktime_t){ .tv64 = (u64) (lhs).tv64 + (rhs).tv64 }; }) + +/* * Add a ktime_t variable and a scalar nanosecond value. * res = kt + nsval: */ --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -312,7 +312,7 @@ EXPORT_SYMBOL_GPL(__ktime_divns); */ ktime_t ktime_add_safe(const ktime_t lhs, const ktime_t rhs) { - ktime_t res = ktime_add(lhs, rhs); + ktime_t res = ktime_add_unsafe(lhs, rhs);

/* * We use KTIME_SEC_MAX here, the maximum timeout which we can

Patches currently in stable-queue which might be from vegard.nossum@oracle.com are

queue-4.4/time-avoid-undefined-behaviour-in-ktime_add_safe.patch