linux-kernel - Re: [dm-devel] [PATCH v2 10/11] crypto: ahash: Remove VLA usage for AHASH_REQUEST_ON

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Message-ID: <20180626091958.zy3m24sjukfbn7av@gondor.apana.org.au>
Date:   Tue, 26 Jun 2018 17:19:59 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Giovanni Cabiddu <giovanni.cabiddu@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        Eric Biggers <ebiggers@...gle.com>,
        Mike Snitzer <snitzer@...hat.com>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        qat-linux@...el.com, linux-kernel@...r.kernel.org,
        dm-devel@...hat.com, linux-crypto@...r.kernel.org,
        Lars Persson <larper@...s.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alasdair Kergon <agk@...hat.com>,
        Rabin Vincent <rabinv@...s.com>
Subject: Re: [dm-devel] [PATCH v2 10/11] crypto: ahash: Remove VLA usage for
 AHASH_REQUEST_ON_STACK

On Mon, Jun 25, 2018 at 03:56:09PM -0700, Eric Biggers wrote:
>
> > diff --git a/include/crypto/internal/hash.h b/include/crypto/internal/hash.h
> > index a0b0ad9d585e..d96ae5f52125 100644
> > --- a/include/crypto/internal/hash.h
> > +++ b/include/crypto/internal/hash.h
> > @@ -142,6 +142,7 @@ static inline struct ahash_alg *__crypto_ahash_alg(struct crypto_alg *alg)
> >  static inline void crypto_ahash_set_reqsize(struct crypto_ahash *tfm,
> >  					    unsigned int reqsize)
> >  {
> > +	BUG_ON(reqsize > AHASH_MAX_REQSIZE);
> >  	tfm->reqsize = reqsize;
> >  }
> 
> This isn't accounting for the cases where a hash algorithm is "wrapped" with
> another one, which increases the request size.  For example, "sha512_mb" ends up
> with a request size of

I think this patch is on the wrong track.  The stack requests are
only ever meant to be used for synchronous algorithms (IOW shash
algorithms) and were a quick-and-dirty fix for legacy users.

So either check SHASH_MAX_REQSIZE or just convert the users to
kmalloc or even better make them real async users.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt