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SubjectRe: BUG: unable to handle kernel NULL pointer dereference in __generic_file_write_iter
On Thu, Feb 21, 2019 at 11:36:24AM -0800, Andrew Morton wrote:
> On Thu, 21 Feb 2019 06:52:04 -0800 syzbot <syzbot+ca95b2b7aef9e7cbd6ab@syzkaller.appspotmail.com> wrote:
>
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit: 4aa9fc2a435a Revert "mm, memory_hotplug: initialize struct..
> > git tree: upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1101382f400000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=4fceea9e2d99ac20
> > dashboard link: https://syzkaller.appspot.com/bug?extid=ca95b2b7aef9e7cbd6ab
> > compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> >
> > Unfortunately, I don't have any reproducer for this crash yet.
>
> Not understanding. That seems to be saying that we got a NULL pointer
> deref in __generic_file_write_iter() at
>
> written = generic_perform_write(file, from, iocb->ki_pos);
>
> which isn't possible.
>
> I'm not seeing recent changes in there which could have caused this. Help.

FWIW, the panic happened in generic_perform_write() when it called
a_ops->write_begin, which was NULL.

I agree with Jann that the unwinders should handle this scenario better.

--
Josh

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