Messages in this thread | | | Subject | Re: [syzbot] BUG: unable to handle kernel access to user memory in sock_ioctl | From | Ben Dooks <> | Date | Mon, 15 Mar 2021 14:41:42 +0000 |
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On 15/03/2021 11:52, Dmitry Vyukov wrote: > On Mon, Mar 15, 2021 at 12:30 PM Ben Dooks <ben.dooks@codethink.co.uk> wrote: >> >> On 14/03/2021 11:03, Dmitry Vyukov wrote: >>> On Sun, Mar 14, 2021 at 11:01 AM Dmitry Vyukov <dvyukov@google.com> wrote: >>>>> On Wed, Mar 10, 2021 at 7:28 PM syzbot >>>>> <syzbot+c23c5421600e9b454849@syzkaller.appspotmail.com> wrote: >>>>>> >>>>>> Hello, >>>>>> >>>>>> syzbot found the following issue on: >>>>>> >>>>>> HEAD commit: 0d7588ab riscv: process: Fix no prototype for arch_dup_tas.. >>>>>> git tree: git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git fixes >>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=122c343ad00000 >>>>>> kernel config: https://syzkaller.appspot.com/x/.config?x=e3c595255fb2d136 >>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=c23c5421600e9b454849 >>>>>> userspace arch: riscv64 >>>>>> >>>>>> Unfortunately, I don't have any reproducer for this issue yet. >>>>>> >>>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit: >>>>>> Reported-by: syzbot+c23c5421600e9b454849@syzkaller.appspotmail.com >>>>> >>>>> +riscv maintainers >>>>> >>>>> Another case of put_user crashing. >>>> >>>> There are 58 crashes in sock_ioctl already. Somehow there is a very >>>> significant skew towards crashing with this "user memory without >>>> uaccess routines" in schedule_tail and sock_ioctl of all places in the >>>> kernel that use put_user... This looks very strange... Any ideas >>>> what's special about these 2 locations? >>> >>> I could imagine if such a crash happens after a previous stack >>> overflow and now task data structures are corrupted. But f_getown does >>> not look like a function that consumes way more than other kernel >>> syscalls... >> >> The last crash I looked at suggested somehow put_user got re-entered >> with the user protection turned back on. Either there is a path through >> one of the kernel handlers where this happens or there's something >> weird going on with qemu. > > Is there any kind of tracking/reporting that would help to localize > it? I could re-reproduce with that code.
I'm not sure. I will have a go at debugging on qemu today just to make sure I can reproduce here before I have to go into the office and fix my Icicle board for real hardware tests.
I think my first plan post reproduction is to stuff some trace points into the fault handlers to see if we can get a idea of faults being processed, etc.
Maybe also add a check in the fault handler to see if the fault was in a fixable region and post an error if that happens / maybe retry the instruction with the relevant SR_SUM flag set.
Hopefully tomorrow I can get a run on real hardware to confirm. Would have been better if the Unmatched board I ordered last year would turn up.
-- Ben Dooks http://www.codethink.co.uk/ Senior Engineer Codethink - Providing Genius
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