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Date:   Wed, 3 Nov 2021 17:01:22 +0000
From:   Lee Jones <lee.jones@linaro.org>
To:     syzbot <syzbot+9671693590ef5aad8953@syzkaller.appspotmail.com>
Cc:     asml.silence@gmail.com, axboe@kernel.dk, io-uring@vger.kernel.org,
        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] KASAN: stack-out-of-bounds Read in iov_iter_revert
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References: <6f7d4c1d-f923-3ab1-c525-45316b973c72@gmail.com>
 <00000000000047f3b805c962affb@google.com>
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Good afternoon Pavel,

> syzbot has tested the proposed patch and the reproducer did not trigger any issue:
> 
> Reported-and-tested-by: syzbot+9671693590ef5aad8953@syzkaller.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?

Any help would be gratefully received.

Kind regards,
Lee

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