dns_resolver: Allow used keys to be invalidated

Allow used DNS resolver keys to be invalidated after use if the caller is
doing its own caching of the results.  This reduces the amount of resources
required.

Fix AFS to invalidate DNS results to kill off permanent failure records
that get lodged in the resolver keyring and prevent future lookups from
happening.

Fixes: 0a5143f2f8 ("afs: Implement VL server rotation")
Signed-off-by: David Howells <dhowells@redhat.com>

net/ceph/messenger.c

@@ -1889,7 +1889,7 @@ static int ceph_dns_resolve_name(const char *name, size_t namelen,
 		return -EINVAL;
 
 	/* do dns_resolve upcall */
-	ip_len = dns_query(NULL, name, end - name, NULL, &ip_addr, NULL);
+	ip_len = dns_query(NULL, name, end - name, NULL, &ip_addr, NULL, false);
 	if (ip_len > 0)
 		ret = ceph_pton(ip_addr, ip_len, ss, -1, NULL);
 	else

net/dns_resolver/dns_query.c

@@ -54,6 +54,7 @@
  * @options: Request options (or NULL if no options)
  * @_result: Where to place the returned data (or NULL)
  * @_expiry: Where to store the result expiry time (or NULL)
+ * @invalidate: Always invalidate the key after use
  *
  * The data will be returned in the pointer at *result, if provided, and the
  * caller is responsible for freeing it.
@@ -69,7 +70,8 @@
  * Returns the size of the result on success, -ve error code otherwise.
  */
 int dns_query(const char *type, const char *name, size_t namelen,
-	      const char *options, char **_result, time64_t *_expiry)
+	      const char *options, char **_result, time64_t *_expiry,
+	      bool invalidate)
 {
 	struct key *rkey;
 	struct user_key_payload *upayload;
@@ -157,6 +159,8 @@ int dns_query(const char *type, const char *name, size_t namelen,
 	ret = len;
 put:
 	up_read(&rkey->sem);
+	if (invalidate)
+		key_invalidate(rkey);
 	key_put(rkey);
 out:
 	kleave(" = %d", ret);