linux-kernel - Re: [syzbot] KASAN: stack-out-of-bounds Read in iov_iter

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Date:   Thu, 16 Dec 2021 17:02:52 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Pavel Begunkov <asml.silence@...il.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        syzbot <syzbot+9671693590ef5aad8953@...kaller.appspotmail.com>,
        io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [syzbot] KASAN: stack-out-of-bounds Read in iov_iter_revert

On Wed, 15 Dec 2021, Pavel Begunkov wrote:

> On 12/15/21 08:06, Lee Jones wrote:
> > On Tue, 09 Nov 2021, Lee Jones wrote:
> > 
> > > On Mon, 08 Nov 2021, Jens Axboe wrote:
> > > > On 11/8/21 8:29 AM, Pavel Begunkov wrote:
> > > > > 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@...kaller.appspotmail.com
> > > > > > > 
> > > > > > > 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@kroah.com/
> > > > > > 
> > > > > > 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@...nel.dk>
> > > > > Date:   Fri Sep 10 11:18:36 2021 -0600
> > > > > 
> > > > >       iov_iter: add helper to save iov_iter state
> > > > > 
> > > > > commit cd65869512ab5668a5d16f789bc4da1319c435c4
> > > > > Author: Jens Axboe <axboe@...nel.dk>
> > > > > Date:   Fri Sep 10 11:19:14 2021 -0600
> > > > > 
> > > > >       io_uring: use iov_iter state save/restore helpers
> > > > 
> > > > Yes, I think backporting based on the save/restore setup is the
> > > > sanest way by far.
> > > 
> > > Would you be kind enough to attempt to send these patches to Stable?
> > > 
> > > When I tried to back-port them, the second one gave me trouble.  And
> > > without the in depth knowledge of the driver/subsystem that you guys
> > > have, I found it almost impossible to resolve all of the conflicts:
> > 
> > Any movement on this chaps?
> > 
> > Not sure I am able to do this back-port without your help.
> 
> Apologies, slipped from my attention, we'll backport it,
> and thanks for the reminder

Excellent.  Thanks Pavel.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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