Re: UBSAN: Undefined error in time.h signed integer overflow

[John Stultz]

On Tue, Sep 5, 2017 at 9:30 PM, Shankara Pailoor <sp3485@xxxxxxxxxxxx> wrote:
> Hi,
>
> I encountered this bug while fuzzing linux kernel 4.13-rc7 with syzkaller.
>
> ================================================================================
> UBSAN: Undefined behaviour in ./include/linux/time.h:233:27
> signed integer overflow:
> 8391720337152500783 * 1000000000 cannot be represented in type 'long int'
> CPU: 0 PID: 31798 Comm: syz-executor2 Not tainted 4.13.0-rc7 #2
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> Ubuntu-1.8.2-1ubuntu1 04/01/2014
> Call Trace:
>  __dump_stack lib/dump_stack.c:16 [inline]
>  dump_stack+0xf7/0x1ae lib/dump_stack.c:52
>  ubsan_epilogue+0x12/0x8f lib/ubsan.c:164
>  handle_overflow+0x21e/0x292 lib/ubsan.c:195
>  __ubsan_handle_mul_overflow+0x2a/0x3e lib/ubsan.c:219
>  timespec_to_ns include/linux/time.h:233 [inline]
>  posix_cpu_timer_set+0xb5c/0xf20 kernel/time/posix-cpu-timers.c:686
>  do_timer_settime+0x1f4/0x390 kernel/time/posix-timers.c:890
>  SYSC_timer_settime kernel/time/posix-timers.c:916 [inline]
>  SyS_timer_settime+0xea/0x170 kernel/time/posix-timers.c:902
>  entry_SYSCALL_64_fastpath+0x18/0xad
> RIP: 0033:0x451e59
> RSP: 002b:00007fb62af4fc08 EFLAGS: 00000216 ORIG_RAX: 00000000000000df
> RAX: ffffffffffffffda RBX: 0000000000718000 RCX: 0000000000451e59
> RDX: 0000000020006000 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: 0000000000000046 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000020003fe0 R11: 0000000000000216 R12: 00000000004be920
> R13: 00000000ffffffff R14: ffffffffffffffff R15: 0000000000000000
> ================================================================================

Looks similar to the issue Thomas fixed here:
   https://patchwork.kernel.org/patch/9799827/


Thomas: Should we change timespec_to_ns() to use the same transition
internally rather then trying to track all the callers?

thanks
-john