Re: [RFC PATCH] posix-cpu-timers: Avoid undefined behaviour in timespec64_to_ns()

[Deepa Dinamani]

On Tue, Feb 26, 2019 at 6:07 PM Xiongfeng Wang
<wangxiongfeng2@xxxxxxxxxx> wrote:
>
> When I ran Syzkaller testsuite, I got the following call trace.
> ================================================================================
> UBSAN: Undefined behaviour in ./include/linux/time64.h:120:27
> signed integer overflow:
> 8243129037239968815 * 1000000000 cannot be represented in type 'long long int'
> CPU: 5 PID: 28854 Comm: syz-executor.1 Not tainted 4.19.24 #4
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.0-0-g63451fca13-prebuilt.qemu-project.org 04/01/2014
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0xca/0x13e lib/dump_stack.c:113
>  ubsan_epilogue+0xe/0x81 lib/ubsan.c:159
>  handle_overflow+0x193/0x1e2 lib/ubsan.c:190
>  timespec64_to_ns include/linux/time64.h:120 [inline]
>  posix_cpu_timer_set+0x95a/0xb70 kernel/time/posix-cpu-timers.c:687
>  do_timer_settime+0x198/0x2a0 kernel/time/posix-timers.c:892
>  __do_sys_timer_settime kernel/time/posix-timers.c:918 [inline]
>  __se_sys_timer_settime kernel/time/posix-timers.c:904 [inline]
>  __x64_sys_timer_settime+0x18d/0x260 kernel/time/posix-timers.c:904
>  do_syscall_64+0xc8/0x580 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x462eb9
> Code: f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f14e4127c58 EFLAGS: 00000246 ORIG_RAX: 00000000000000df
> RAX: ffffffffffffffda RBX: 000000000073bfa0 RCX: 0000000000462eb9
> RDX: 0000000020000080 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: 0000000000000004 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007f14e41286bc
> R13: 00000000004c54cc R14: 0000000000704278 R15: 00000000ffffffff
> ================================================================================
>
> This patch use 'timespec64_to_ktime()' to limit 'tv_sec' to avoid
> overflow.
>
> Signed-off-by: Xiongfeng Wang <wangxiongfeng2@xxxxxxxxxx>
> ---
>  kernel/time/posix-cpu-timers.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
> index 80f9552..f7e3929 100644
> --- a/kernel/time/posix-cpu-timers.c
> +++ b/kernel/time/posix-cpu-timers.c
> @@ -684,7 +684,7 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
>          * Install the new reload setting, and
>          * set up the signal and overrun bookkeeping.
>          */
> -       timer->it.cpu.incr = timespec64_to_ns(&new->it_interval);
> +       timer->it.cpu.incr = ktime_to_ns(timespec64_to_ktime(new->it_interval));
>         timer->it_interval = ns_to_ktime(timer->it.cpu.incr);
>
>         /*

This seems like a similar bug as the other one
https://lkml.org/lkml/2019/2/24/214. Maybe it makes sense here also to
do some bounds checking when we get the userspace parameter.
This patch just saturates the value.

-Deepa