Re: [syzbot] KASAN: stack-out-of-bounds Read in iov_iter_revert

[Pavel Begunkov]

On 11/3/21 17:01, Lee Jones wrote:
> Good afternoon Pavel,
>
> > syzbot has tested the proposed patch and the reproducer did not trigger any issue:
> >
> > Reported-and-tested-by: syzbot+9671693590ef5aad8953@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > Tested on:
> >
> > commit:         bff2c168 io_uring: don't retry with truncated iter
> > git tree:       https://github.com/isilence/linux.git truncate
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=730106bfb5bf8ace
> > dashboard link: https://syzkaller.appspot.com/bug?extid=9671693590ef5aad8953
> > compiler:       Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.1
> >
> > Note: testing is done by a robot and is best-effort only.
>
> As you can see in the 'dashboard link' above this bug also affects
> android-5-10 which is currently based on v5.10.75.
>
> I see that the back-port of this patch failed in v5.10.y:
>
>    https://lore.kernel.org/stable/163152589512611@xxxxxxxxx/
>
> And after solving the build-error by back-porting both:
>
>    2112ff5ce0c11 iov_iter: track truncated size
>    89c2b3b749182 io_uring: reexpand under-reexpanded iters
>
> I now see execution tripping the WARN() in iov_iter_revert():
>
>    if (WARN_ON(unroll > MAX_RW_COUNT))
>        return
>
> Am I missing any additional patches required to fix stable/v5.10.y?

Is it the same syz test? There was a couple more patches for
IORING_SETUP_IOPOLL, but strange if that's not the case.


fwiw, Jens decided to replace it with another mechanism shortly
after, so it may be a better idea to backport those. Jens,
what do you think?


commit 8fb0f47a9d7acf620d0fd97831b69da9bc5e22ed
Author: Jens Axboe <axboe@xxxxxxxxx>
Date:   Fri Sep 10 11:18:36 2021 -0600

    iov_iter: add helper to save iov_iter state

commit cd65869512ab5668a5d16f789bc4da1319c435c4
Author: Jens Axboe <axboe@xxxxxxxxx>
Date:   Fri Sep 10 11:19:14 2021 -0600

    io_uring: use iov_iter state save/restore helpers


--
Pavel Begunkov