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Date:   Wed, 12 May 2021 13:04:37 -0700
From:   Eric Biggers <ebiggers@kernel.org>
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     linux-crypto@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        herbert@gondor.apana.org.au, will@kernel.org,
        kernel-team@android.com
Subject: Re: [PATCH v3 1/7] crypto: handle zero sized AEAD inputs correctly
Message-ID: <YJw01Z3oxwY5Sfpa@gmail.com>
References: <20210512184439.8778-1-ardb@kernel.org>
 <20210512184439.8778-2-ardb@kernel.org>
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On Wed, May 12, 2021 at 08:44:33PM +0200, Ard Biesheuvel wrote:
> There are corner cases where skcipher_walk_aead_[en|de]crypt() may be
> invoked with a zero sized input, which is not rejected by the walker
> code, but results in the skcipher_walk structure to not be fully
> initialized. This will leave stale values in its page and buffer
> members, which will be subsequently passed to kfree() or free_page() by
> skcipher_walk_done(), resulting in a crash if those routines fail to
> identify them as in valid inputs.
> 
> Fix this by setting page and buffer to NULL even if the size of the
> input is zero.
> 
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Is this fixing an existing bug, or only a bug that got exposed by this patchset?
It would be helpful to make that clear (and if it fixes an existing bug, include
a Fixes tag).

Also, skcipher_walk_virt() doesn't set page and buffer to NULL, as it is
currently expected that skcipher_walk_done() is only called when
walk.nbytes != 0.  Is something different for skcipher_walk_aead_[en|de]crypt()?

- Eric