ima: fix reference leak in asymmetric_verify()

Don't leak a reference to the key if its algorithm is unknown.

Fixes: 947d705 ("ima: Support EC keys for signature verification")
Cc: <stable@vger.kernel.org> # v5.13+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

Author: ebiggers

security/integrity/digsig_asymmetric.c

@@ -109,22 +109,25 @@ int asymmetric_verify(struct key *keyring, const char *sig,
 
 	pk = asymmetric_key_public_key(key);
 	pks.pkey_algo = pk->pkey_algo;
-	if (!strcmp(pk->pkey_algo, "rsa"))
+	if (!strcmp(pk->pkey_algo, "rsa")) {
 		pks.encoding = "pkcs1";
-	else if (!strncmp(pk->pkey_algo, "ecdsa-", 6))
+	} else if (!strncmp(pk->pkey_algo, "ecdsa-", 6)) {
 		/* edcsa-nist-p192 etc. */
 		pks.encoding = "x962";
-	else if (!strcmp(pk->pkey_algo, "ecrdsa") ||
-		   !strcmp(pk->pkey_algo, "sm2"))
+	} else if (!strcmp(pk->pkey_algo, "ecrdsa") ||
+		   !strcmp(pk->pkey_algo, "sm2")) {
 		pks.encoding = "raw";
-	else
-		return -ENOPKG;
+	} else {
+		ret = -ENOPKG;
+		goto out;
+	}
 
 	pks.digest = (u8 *)data;
 	pks.digest_size = datalen;
 	pks.s = hdr->sig;
 	pks.s_size = siglen;
 	ret = verify_signature(key, &pks);
+out:
 	key_put(key);
 	pr_debug("%s() = %d\n", __func__, ret);
 	return ret;