linux-kernel - Re: [syzbot] [zstd] UBSAN: array-index-out-of-bounds in FSE_decompress_wksp_body

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Message-ID: <20231007210556.GA174883@sol.localdomain>
Date:   Sat, 7 Oct 2023 14:05:56 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Nick Terrell <terrelln@...com>
Cc:     syzbot <syzbot+1f2eb3e8cd123ffce499@...kaller.appspotmail.com>,
        clm@...com, dsterba@...e.com, josef@...icpanda.com,
        linux-btrfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        terrelln@...com, linux-hardening@...r.kernel.org
Subject: Re: [syzbot] [zstd] UBSAN: array-index-out-of-bounds in
 FSE_decompress_wksp_body_bmi2

Hi Nick,

On Wed, Aug 30, 2023 at 12:49:53AM -0700, syzbot wrote:
> UBSAN: array-index-out-of-bounds in lib/zstd/common/fse_decompress.c:345:30
> index 33 is out of range for type 'FSE_DTable[1]' (aka 'unsigned int[1]')

Zstandard needs to be converted to use C99 flex-arrays instead of length-1
arrays.  https://github.com/facebook/zstd/pull/3785 would fix this in upstream
Zstandard, though it doesn't work well with the fact that upstream Zstandard
supports C90.  Not sure how you want to handle this.

- Eric