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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Tue, 17 Aug 2021 16:18:53 +0200
Message-ID: <CAMj1kXGjY-EfaLc47HKvFz8AKeT=+XTXNRR5kVbQV7s3Hi9C2g@mail.gmail.com>
Subject: Re: [PATCH] crypto: xts_crypt() return if walk.nbytes is 0
To:     Shreyansh Chouhan <chouhan.shreyansh630@gmail.com>
Cc:     Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        syzbot+20191dc583eff8602d2d@syzkaller.appspotmail.com
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On Mon, 9 Aug 2021 at 16:10, Shreyansh Chouhan
<chouhan.shreyansh630@gmail.com> wrote:
>
> xts_crypt() code doesn't call kernel_fpu_end() after calling
> kernel_fpu_begin() if walk.nbytes is 0. The correct behavior should be
> not calling kernel_fpu_begin() if walk.nbytes is 0.
>
> Reported-by: syzbot+20191dc583eff8602d2d@syzkaller.appspotmail.com
> Signed-off-by: Shreyansh Chouhan <chouhan.shreyansh630@gmail.com>

Acked-by: Ard Biesheuvel <ardb@kernel.org>

> ---
>  arch/x86/crypto/aesni-intel_glue.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/crypto/aesni-intel_glue.c b/arch/x86/crypto/aesni-intel_glue.c
> index 388643ca2177..ec6eac57c493 100644
> --- a/arch/x86/crypto/aesni-intel_glue.c
> +++ b/arch/x86/crypto/aesni-intel_glue.c
> @@ -849,7 +849,7 @@ static int xts_crypt(struct skcipher_request *req, bool encrypt)
>                 return -EINVAL;
>
>         err = skcipher_walk_virt(&walk, req, false);
> -       if (err)
> +       if (err || !walk.nbytes)
>                 return err;
>
>         if (unlikely(tail > 0 && walk.nbytes < walk.total)) {
> --
> 2.31.1
>