crypto: af_alg - Disallow multiple in-flight AIO requests

Having multiple in-flight AIO requests results in unpredictable
output because they all share the same IV.  Fix this by only allowing
one request at a time.

Fixes: 83094e5e ("crypto: af_alg - add async support to algif_aead")
Fixes: a596999b ("crypto: algif - change algif_skcipher to be asynchronous")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/af_alg.c

@@ -1116,9 +1116,13 @@ EXPORT_SYMBOL_GPL(af_alg_sendmsg);
 void af_alg_free_resources(struct af_alg_async_req *areq)
 {
 	struct sock *sk = areq->sk;
+	struct af_alg_ctx *ctx;
 
 	af_alg_free_areq_sgls(areq);
 	sock_kfree_s(sk, areq, areq->areqlen);
+
+	ctx = alg_sk(sk)->private;
+	ctx->inflight = false;
 }
 EXPORT_SYMBOL_GPL(af_alg_free_resources);
 
@@ -1188,11 +1192,19 @@ EXPORT_SYMBOL_GPL(af_alg_poll);
 struct af_alg_async_req *af_alg_alloc_areq(struct sock *sk,
 					   unsigned int areqlen)
 {
-	struct af_alg_async_req *areq = sock_kmalloc(sk, areqlen, GFP_KERNEL);
+	struct af_alg_ctx *ctx = alg_sk(sk)->private;
+	struct af_alg_async_req *areq;
+
+	/* Only one AIO request can be in flight. */
+	if (ctx->inflight)
+		return ERR_PTR(-EBUSY);
 
+	areq = sock_kmalloc(sk, areqlen, GFP_KERNEL);
 	if (unlikely(!areq))
 		return ERR_PTR(-ENOMEM);
 
+	ctx->inflight = true;
+
 	areq->areqlen = areqlen;
 	areq->sk = sk;
 	areq->first_rsgl.sgl.sgt.sgl = areq->first_rsgl.sgl.sgl;

include/crypto/if_alg.h

@@ -136,6 +136,7 @@ struct af_alg_async_req {
  *			recvmsg is invoked.
  * @init:		True if metadata has been sent.
  * @len:		Length of memory allocated for this data structure.
+ * @inflight:		Non-zero when AIO requests are in flight.
  */
 struct af_alg_ctx {
 	struct list_head tsgl_list;
@@ -154,6 +155,8 @@ struct af_alg_ctx {
 	bool init;
 
 	unsigned int len;
+
+	unsigned int inflight;
 };
 
 int af_alg_register_type(const struct af_alg_type *type);