Re: [net] 6ef3f95797: UBSAN:shift-out-of-bounds_in_kernel/time/timer.c

[Artem Savkov <asavkov@redhat.com>]

On Sat, Apr 02, 2022 at 11:09:40AM +0800, kernel test robot wrote:
> 
> 
> Greeting,
> 
> FYI, we noticed the following commit (built with gcc-9):
> 
> commit: 6ef3f95797546781829db3bb6228c9990ba1d49f ("[PATCH v3 2/2] net: make tcp keepalive timer upper bound")
> url: https://github.com/intel-lab-lkp/linux/commits/Artem-Savkov/timer-add-a-function-to-adjust-timeouts-to-be-upper-bound/20220330-172140
> base: https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git b166e52541f2357ce126a92ce1d9a580fdca719d
> patch link: https://lore.kernel.org/netdev/20220330082046.3512424-3-asavkov@redhat.com
> 
> in testcase: kernel-selftests
> version: kernel-selftests-x86_64-a17aac1b-1_20220328
> with following parameters:
> 
> 	group: tc-testing
> 	ucode: 0xec
> 
> test-description: The kernel contains a set of "self tests" under the tools/testing/selftests/ directory. These are intended to be small unit tests to exercise individual code paths in the kernel.
> test-url: https://www.kernel.org/doc/Documentation/kselftest.txt
> 
> 
> on test machine: 8 threads Intel(R) Core(TM) i7-6700 CPU @ 3.40GHz with 16G memory
> 
> caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
> 
> 
> 
> If you fix the issue, kindly add following tag
> Reported-by: kernel test robot <oliver.sang@intel.com>
> 
> 
> [  158.913672][    C1] UBSAN: shift-out-of-bounds in kernel/time/timer.c:584:32
> [  158.922603][    C1] shift exponent -3 is negative

This is caused by LVL_START(0). Levels 0 and 1 need to be handled
separately to insure we don't end up with negative values.

-- 
 Artem