Re: KASAN: slab-out-of-bounds Read in bpf_skb_change_proto

[Daniel Borkmann]

On 06/11/2018 11:52 AM, Dmitry Vyukov wrote:
> On Mon, Jun 11, 2018 at 11:42 AM, Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
>> On 06/10/2018 05:27 PM, syzbot wrote:
>>> Hello,
>>>
>>> syzbot found the following crash on:
>>>
>>> HEAD commit:    a16afaf7928b Merge tag 'for-v4.18' of git://git.kernel.org..
>>> git tree:       upstream
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=1338f6bf800000
>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=314f2150f36c16ca
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=d2d729bdde65dee3eae6
>>> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>>> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=1173381f800000
>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=171f90cf800000
>>>
>>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>>> Reported-by: syzbot+d2d729bdde65dee3eae6@xxxxxxxxxxxxxxxxxxxxxxxxx
>>
>> #syz fix: bpf: reject passing modified ctx to helper functions
> 
> On a related note, it seems that it still can unwind past
> bpf_skb_change_proto. I think the "net.core.bpf_jit_kallsyms = 1"
> sysctl should have been reached syzbot by the time of crash. Are you
> sure that's the only thing requires? We are using frame pointer
> unwinder just in case.

Nah, I know what happened; just sent a PR fix for syzkaller.

Thanks,
Daniel