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Date:   Thu, 4 Feb 2021 16:53:26 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Phillip Lougher <phillip@...ashfs.org.uk>
Cc:     linux-kernel@...r.kernel.org,
        syzbot+6fba78f99b9afd4b5634@...kaller.appspotmail.com
Subject: Re: [PATCH 1/4] Squashfs: avoid out of bounds writes in
 decompressors

On Thu,  4 Feb 2021 13:02:46 +0000 Phillip Lougher <phillip@...ashfs.org.uk> wrote:

> This is a regression introduced by the patch "migrate from ll_rw_block
> usage to BIO".

Fixes: 93e72b3c612adc ("squashfs: migrate from ll_rw_block usage to BIO")

> Sysbot/Syskaller has reported a number of "out of bounds writes" and
> "unable to handle kernel paging request in squashfs_decompress" errors
> which have been identified as a regression introduced by the above patch.
> 
> Specifically, the patch removed the following sanity check
> 
> if (length < 0 || length > output->length ||
> 		(index + length) > msblk->bytes_used)
> 
> This check did two things:
> 
> 1. It ensured any reads were not beyond the end of the filesystem
> 
> 2. It ensured that the "length" field read from the filesystem
>    was within the expected maximum length.  Without this any
>    corrupted values can over-run allocated buffers.
> 

All sounds fairly serious.  Should I add a cc:stable to this?

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