linux-kernel - Re: [PATCH] crypto: drbg: fix crypto api abuse

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Date:   Wed, 23 Feb 2022 17:47:23 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Gilad Ben-Yossef <gilad@...yossef.com>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Ofir Drang <ofir.drang@....com>,
        Corentin Labbe <clabbe.montjoie@...il.com>,
        stable@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crypto: drbg: fix crypto api abuse

On Wed, Feb 23, 2022 at 10:04:00AM +0200, Gilad Ben-Yossef wrote:
> the drbg code was binding the same buffer to two different
> scatter gather lists and submitting those as source and
> destination to a crypto api operation, thus potentially
> causing HW crypto drivers to perform overlapping DMA
> mappings which are not aware it is the same buffer.
> 
> This can have serious consequences of data corruption of
> internal DRBG buffers and wrong RNG output.
> 
> Fix this by reusing the same scatter gatther list for both
> src and dst.
> 
> Signed-off-by: Gilad Ben-Yossef <gilad@...yossef.com>
> Reported-by: Corentin Labbe <clabbe.montjoie@...il.com>
> Tested-by: Corentin Labbe <clabbe.montjoie@...il.com>
> Tested-on: r8a7795-salvator-x
> Tested-on: xilinx-zc706
> Fixes: 43490e8046b5d ("crypto: drbg - in-place cipher operation for CTR")
> Cc: stable@...r.kernel.org

Where is it documented and tested that the API doesn't allow this?
I wasn't aware of this case; it sounds perfectly allowed to me.
There might be a lot of other users who do this, not just drbg.c.

- Eric