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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Tue, 28 May 2019 15:03:44 +0200
Message-ID: <CAKv+Gu-Bzb6bucFXgW+EgU2bh9Kp-rAJWq5TSNrk7n_rMGkx9g@mail.gmail.com>
Subject: Re: [PATCH] arm64 sha1-ce finup: correct digest for empty data
To:     Elena Petrova <lenaptr@google.com>
Cc:     "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@vger.kernel.org>, stable <stable@vger.kernel.org>
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On Tue, 28 May 2019 at 14:42, Elena Petrova <lenaptr@google.com> wrote:
>
> The sha1-ce finup implementation for ARM64 produces wrong digest
> for empty input (len=0). Expected: da39a3ee..., result: 67452301...
> (initial value of SHA internal state). The error is in sha1_ce_finup:
> for empty data `finalize` will be 1, so the code is relying on
> sha1_ce_transform to make the final round. However, in
> sha1_base_do_update, the block function will not be called when
> len == 0.
>
> Fix it by setting finalize to 0 if data is empty.
>
> Fixes: 07eb54d306f4 ("crypto: arm64/sha1-ce - move SHA-1 ARMv8 implementation to base layer")
> Cc: stable@vger.kernel.org
> Signed-off-by: Elena Petrova <lenaptr@google.com>

Thanks for the fix

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

It looks like the sha224/256 suffers from the same issue. Would you
mind sending out a fix for that as well? Thanks.

> ---
>  arch/arm64/crypto/sha1-ce-glue.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/crypto/sha1-ce-glue.c b/arch/arm64/crypto/sha1-ce-glue.c
> index eaa7a8258f1c..0652f5f07ed1 100644
> --- a/arch/arm64/crypto/sha1-ce-glue.c
> +++ b/arch/arm64/crypto/sha1-ce-glue.c
> @@ -55,7 +55,7 @@ static int sha1_ce_finup(struct shash_desc *desc, const u8 *data,
>                          unsigned int len, u8 *out)
>  {
>         struct sha1_ce_state *sctx = shash_desc_ctx(desc);
> -       bool finalize = !sctx->sst.count && !(len % SHA1_BLOCK_SIZE);
> +       bool finalize = !sctx->sst.count && !(len % SHA1_BLOCK_SIZE) && len;
>
>         if (!crypto_simd_usable())
>                 return crypto_sha1_finup(desc, data, len, out);
> --
> 2.22.0.rc1.257.g3120a18244-goog
>