[dm-devel] [PATCH] crypto/mcryptd: Check mcryptd algorithm compatability

[Tim Chen]

On Mon, 2016-12-05 at 20:34 +0800, Herbert Xu wrote:
> On Fri, Dec 02, 2016 at 04:15:21PM -0800, Tim Chen wrote:
> > 
> > Algorithms not compatible with mcryptd could be spawned by mcryptd
> > with a direct crypto_alloc_tfm invocation using a "mcryptd(alg)"
> > name construct.  This causes mcryptd to crash the kernel if
> > "alg" is incompatible and not intended to be used with mcryptd.
> > 
> > A flag CRYPTO_ALG_MCRYPT is being added to mcryptd compatible
> > algorithms' cra_flags. The compatability is checked when mcryptd spawn
> > off an algorithm.
> > 
> > Link: http://marc.info/?l=linux-crypto-vger&m=148063683310477&w=2
> > Cc: stable at vger.kernel.org
> > Reported-by: Mikulas Patocka <mpatocka at redhat.com>
> > Tested-by: Megha Dey <megha.dey at linux.intel.com>
> > Signed-off-by: Tim Chen <tim.c.chen at linux.intel.com>
> Tim, I think we should instead make mcryptd refuse to generate
> a non-internal algorithm.  This way the user would not be able
> to access it at all since they can only request for non-internal
> algorithms.
> 
> Basically you want to check at the start of mcryptd_create_hash
> that the INTERNAL bit is set on both the type and mask as returned
> by crypto_get_attr_type.

I have thought about that.  However, not all internal algorithms
are compatible with mcryptd. We can still have trouble if some
random internal algorithm is paired with mcryptd.

Tim