crypto: api - Redo lookup on EEXIST

When two crypto algorithm lookups occur at the same time with
different names for the same algorithm, e.g., ctr(aes-generic)
and ctr(aes), they will both be instantiated.  However, only one
of them can be registered.  The second instantiation will fail
with EEXIST.

Avoid failing the second lookup by making it retry, but only once
because there are tricky names such as gcm_base(ctr(aes),ghash)
that will always fail, despite triggering instantiation and EEXIST.

Reported-by: Ingo Franzki <ifranzki@linux.ibm.com>
Fixes: 2825982 ("[CRYPTO] api: Added event notification")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Author: herbertx

crypto/api.c

@@ -219,10 +219,19 @@ static struct crypto_alg *crypto_larval_wait(struct crypto_alg *alg,
 		if (crypto_is_test_larval(larval))
 			crypto_larval_kill(larval);
 		alg = ERR_PTR(-ETIMEDOUT);
-	} else if (!alg) {
+	} else if (!alg || PTR_ERR(alg) == -EEXIST) {
+		int err = alg ? -EEXIST : -EAGAIN;
+
+		/*
+		 * EEXIST is expected because two probes can be scheduled
+		 * at the same time with one using alg_name and the other
+		 * using driver_name.  Do a re-lookup but do not retry in
+		 * case we hit a quirk like gcm_base(ctr(aes),...) which
+		 * will never match.
+		 */
 		alg = &larval->alg;
 		alg = crypto_alg_lookup(alg->cra_name, type, mask) ?:
-		      ERR_PTR(-EAGAIN);
+		      ERR_PTR(err);
 	} else if (IS_ERR(alg))
 		;
 	else if (crypto_is_test_larval(larval) &&