9p/net: fix possible memory leak in p9_check_errors()

When p9pdu_readf() is called with "s?d" attribute, it allocates a pointer
that will store a string. But when p9pdu_readf() fails while handling "d"
then this pointer will not be freed in p9_check_errors().

Fixes: 51a87c55 ("9p: rework client code to use new protocol support functions")
Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>
Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
Message-ID: <20231027030302.11927-1-hbh25y@gmail.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>

net/9p/client.c

@@ -540,12 +540,14 @@ static int p9_check_errors(struct p9_client *c, struct p9_req_t *req)
 		return 0;
 
 	if (!p9_is_proto_dotl(c)) {
-		char *ename;
+		char *ename = NULL;
 
 		err = p9pdu_readf(&req->rc, c->proto_version, "s?d",
 				  &ename, &ecode);
-		if (err)
+		if (err) {
+			kfree(ename);
 			goto out_err;
+		}
 
 		if (p9_is_proto_dotu(c) && ecode < 512)
 			err = -ecode;