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

[Xiongfeng Wang]

On 2019/2/27 10:38, Deepa Dinamani wrote:
> 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.

Thanks for your advice. I will send another version.

Thanks,
Xiongfeng

> 
> -Deepa
> 
> .
>