Code: static inline void mcryptd_check_internal(struct rtattr **tb, u32 *type,
 					  u32 *mask)
 {
 	struct crypto_attr_type *algt;
 
 	algt = crypto_get_attr_type(tb);
 	if (IS_ERR(algt))
		return;
	if ((algt->type & CRYPTO_ALG_INTERNAL))
		*type |= CRYPTO_ALG_INTERNAL;
	if ((algt->mask & CRYPTO_ALG_INTERNAL))
		*mask |= CRYPTO_ALG_INTERNAL;
 }

Vulnerability Type: DoS 
CWE ID: CWE-476
Summary: crypto/mcryptd.c in the Linux kernel before 4.8.15 allows local users to cause a denial of service (NULL pointer dereference and system crash) by using an AF_ALG socket with an incompatible algorithm, as demonstrated by mcryptd(md5).
Commit Message: crypto: mcryptd - Check mcryptd algorithm compatibility

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 an arbitrary
"alg" is incompatible and not intended to be used with mcryptd.  It is
an issue if AF_ALG tries to spawn mcryptd(alg) to expose it externally.
But such algorithms must be used internally and not be exposed.

We added a check to enforce that only internal algorithms are allowed
with mcryptd at the time mcryptd is spawning an algorithm.

Link: http://marc.info/?l=linux-crypto-vger&m=148063683310477&w=2
Cc: stable@vger.kernel.org
Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>