Code: static int skcipher_accept_parent(void *private, struct sock *sk)
 {
 	struct skcipher_ctx *ctx;
 	struct alg_sock *ask = alg_sk(sk);
	unsigned int len = sizeof(*ctx) + crypto_skcipher_reqsize(private);
 
 	ctx = sock_kmalloc(sk, len, GFP_KERNEL);
 	if (!ctx)
 		return -ENOMEM;
 
	ctx->iv = sock_kmalloc(sk, crypto_skcipher_ivsize(private),
 			       GFP_KERNEL);
 	if (!ctx->iv) {
 		sock_kfree_s(sk, ctx, len);
 		return -ENOMEM;
 	}
 
	memset(ctx->iv, 0, crypto_skcipher_ivsize(private));
 
 	INIT_LIST_HEAD(&ctx->tsgl);
 	ctx->len = len;
	ctx->used = 0;
	ctx->more = 0;
	ctx->merge = 0;
	ctx->enc = 0;
	atomic_set(&ctx->inflight, 0);
	af_alg_init_completion(&ctx->completion);
 
 	ask->private = ctx;
 
	skcipher_request_set_tfm(&ctx->req, private);
 	skcipher_request_set_callback(&ctx->req, CRYPTO_TFM_REQ_MAY_BACKLOG,
 				      af_alg_complete, &ctx->completion);
 
	sk->sk_destruct = skcipher_sock_destruct;

	return 0;
}

Vulnerability Type: DoS 
CWE ID: CWE-476
Summary: crypto/algif_skcipher.c in the Linux kernel before 4.4.2 does not verify that a setkey operation has been performed on an AF_ALG socket before an accept system call is processed, which allows local users to cause a denial of service (NULL pointer dereference and system crash) via a crafted application that does not supply a key, related to the lrw_crypt function in crypto/lrw.c.
Commit Message: crypto: algif_skcipher - Require setkey before accept(2)

Some cipher implementations will crash if you try to use them
without calling setkey first.  This patch adds a check so that
the accept(2) call will fail with -ENOKEY if setkey hasn't been
done on the socket yet.

Cc: stable@vger.kernel.org
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Tested-by: Dmitry Vyukov <dvyukov@google.com>