Re: [dm-devel] [PATCH 1/3 v2] crypto: introduce the flag CRYPTO_ALG_ALLOCATES_MEMORY

Eric Biggers
2020-06-26T17:00:44Z

On Fri, Jun 26, 2020 at 09:46:17AM -0700, Eric Biggers wrote:
> On Fri, Jun 26, 2020 at 12:16:33PM -0400, Mikulas Patocka wrote:
> > +/*
> > + * Pass these flags down through the crypto API.
> > + */
> > +#define CRYPTO_ALG_INHERITED_FLAGS (CRYPTO_ALG_ASYNC | CRYPTO_ALG_ALLOCATES_MEMORY)
>
> This comment is useless. How about:
>
> /*
> * When an algorithm uses another algorithm (e.g., if it's an instance of a
> * template), these are the flags that always get set on the "outer" algorithm
> * if any "inner" algorithm has them set. In some cases other flags are
> * inherited too; these are just the flags that are *always* inherited.
> */
> #define CRYPTO_ALG_INHERITED_FLAGS (CRYPTO_ALG_ASYNC | CRYPTO_ALG_ALLOCATES_MEMORY)
>
> Also I wonder about the case where the inner algorithm is a fallback rather than
> part of a template instance. This patch only handles templates, not fallbacks.
> Is that intentional? Isn't that technically a bug?

Also is CRYPTO_ALG_ALLOCATES_MEMORY meant to apply for algorithms of type
"cipher" and "shash"? The code doesn't handle those, so presumably not?

What about "akcipher"?

> > Index: linux-2.6/crypto/xts.c
> > ===================================================================
> > --- linux-2.6.orig/crypto/xts.c 2020-06-26 17:24:03.566417000 +0200
> > +++ linux-2.6/crypto/xts.c 2020-06-26 17:24:03.566417000 +0200
> > @@ -415,7 +415,7 @@ static int create(struct crypto_template
> > } else
> > goto err_free_inst;
> >
> > - inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC;
> > + inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_INHERITED_FLAGS;
> > inst->alg.base.cra_priority = alg->base.cra_priority;
> > inst->alg.base.cra_blocksize = XTS_BLOCK_SIZE;
> > inst->alg.base.cra_alignmask = alg->base.cra_alignmask |
>
> Need to set the mask correctly in this file.

cryptd_create_skcipher(), cryptd_create_hash(), cryptd_create_aead(), and
crypto_rfc4309_create() are also missing setting the mask.

pcrypt_create_aead() is missing both setting the mask and inheriting the flags.

Also, "seqiv" instances can be created without CRYPTO_ALG_ALLOCATES_MEMORY set,
despite seqiv_aead_encrypt() allocating memory.

- Eric