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From: Ard Biesheuvel <ardb@kernel.org>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Shreyansh Chouhan <chouhan.shreyansh630@gmail.com>,
	"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
Subject: Re: [PATCH] crypto: xts_crypt() return if walk.nbytes is 0
Date: Fri, 20 Aug 2021 13:14:52 +0200	[thread overview]
Message-ID: <CAMj1kXGMPimX0_dR_kLuzZjuJK9rM=uCpRDtoJq0UjWq12M10A@mail.gmail.com> (raw)
In-Reply-To: <20210820083111.GA28484@gondor.apana.org.au>

On Fri, 20 Aug 2021 at 10:31, Herbert Xu <herbert@gondor.apana.org.au> wrote:
>
> On Mon, Aug 09, 2021 at 07:40:27PM +0530, Shreyansh Chouhan 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>
> > ---
> >  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;
>
> The err check is now redundant because when there is an error
> nbytes is always zero.
>

In spite of that, I have a slight preference for this version, given
that it makes it obvious that we bail on two separate conditions:
- an error has occurred
- no error has occurred but the resulting walk is empty

Testing walk.nbytes only needlessly obfuscates the code, as we need to
return 'err' in the end anyway.

  reply	other threads:[~2021-08-20 11:15 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-30 13:41 [PATCH] crypto: add missing kernel_fpu_end() call Shreyansh Chouhan
2021-08-06  8:23 ` Herbert Xu
2021-08-06  9:05   ` Ard Biesheuvel
2021-08-06  9:07     ` Ard Biesheuvel
2021-08-06 10:36       ` Shreyansh Chouhan
2021-08-09 14:10         ` [PATCH] crypto: xts_crypt() return if walk.nbytes is 0 Shreyansh Chouhan
2021-08-17 14:18           ` Ard Biesheuvel
2021-08-20  8:31           ` Herbert Xu
2021-08-20 11:14             ` Ard Biesheuvel [this message]
2021-08-20 12:53               ` Herbert Xu
2021-08-22  3:45                 ` [PATCH v2] " Shreyansh Chouhan
2021-08-27  8:38                   ` Herbert Xu
2021-08-22  3:48                 ` [PATCH] " Shreyansh Chouhan
2021-08-22 13:23                 ` Ard Biesheuvel

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