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