afs: Provide an RCU-capable key lookup

Provide an RCU-capable key lookup function.  We don't want to call
afs_request_key() in RCU-mode pathwalk as request_key() might sleep, even if
we don't ask it to construct anything as it might find a key that is currently
undergoing construction.

Signed-off-by: David Howells <dhowells@redhat.com>

3 files changed, 45 insertions, 3 deletions

diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index f66a3be12fd6..9cdfabaeaa0b 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -1217,6 +1217,7 @@ extern void afs_cache_permit(struct afs_vnode *, struct key *, unsigned int,
                              struct afs_status_cb *);
 extern void afs_zap_permits(struct rcu_head *);
 extern struct key *afs_request_key(struct afs_cell *);
+extern struct key *afs_request_key_rcu(struct afs_cell *);
 extern int afs_check_permit(struct afs_vnode *, struct key *, afs_access_t *);
 extern int afs_permission(struct inode *, int);
 extern void __exit afs_clean_up_permit_cache(void);
diff --git a/fs/afs/security.c b/fs/afs/security.c
index 71e71c07568f..ef2fd34ba282 100644
--- a/fs/afs/security.c
+++ b/fs/afs/security.c
@@ -27,8 +27,37 @@ struct key *afs_request_key(struct afs_cell *cell)
         _enter("{%x}", key_serial(cell->anonymous_key));
 
         _debug("key %s", cell->anonymous_key->description);
-        key = request_key(&key_type_rxrpc, cell->anonymous_key->description,
-                          NULL);
+        key = request_key_net(&key_type_rxrpc, cell->anonymous_key->description,
+                              cell->net->net, NULL);
+        if (IS_ERR(key)) {
+                if (PTR_ERR(key) != -ENOKEY) {
+                        _leave(" = %ld", PTR_ERR(key));
+                        return key;
+                }
+
+                /* act as anonymous user */
+                _leave(" = {%x} [anon]", key_serial(cell->anonymous_key));
+                return key_get(cell->anonymous_key);
+        } else {
+                /* act as authorised user */
+                _leave(" = {%x} [auth]", key_serial(key));
+                return key;
+        }
+}
+
+/*
+ * Get a key when pathwalk is in rcuwalk mode.
+ */
+struct key *afs_request_key_rcu(struct afs_cell *cell)
+{
+        struct key *key;
+
+        _enter("{%x}", key_serial(cell->anonymous_key));
+
+        _debug("key %s", cell->anonymous_key->description);
+        key = request_key_net_rcu(&key_type_rxrpc,
+                                  cell->anonymous_key->description,
+                                  cell->net->net);
         if (IS_ERR(key)) {
                 if (PTR_ERR(key) != -ENOKEY) {
                         _leave(" = %ld", PTR_ERR(key));
diff --git a/include/linux/key.h b/include/linux/key.h
index 50028338a4cc..6cf8e71cf8b7 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -324,7 +324,7 @@ static inline struct key *request_key(struct key_type *type,
 }
 
 #ifdef CONFIG_NET
-/*
+/**
  * request_key_net - Request a key for a net namespace and wait for construction
  * @type: Type of key.
  * @description: The searchable description of the key.
@@ -341,6 +341,18 @@ static inline struct key *request_key(struct key_type *type,
  */
 #define request_key_net(type, description, net, callout_info) \
         request_key_tag(type, description, net->key_domain, callout_info);
+
+/**
+ * request_key_net_rcu - Request a key for a net namespace under RCU conditions
+ * @type: Type of key.
+ * @description: The searchable description of the key.
+ * @net: The network namespace that is the key's domain of operation.
+ *
+ * As for request_key_rcu() except that only keys that operate the specified
+ * network namespace are used.
+ */
+#define request_key_net_rcu(type, description, net) \
+        request_key_rcu(type, description, net->key_domain);
 #endif /* CONFIG_NET */
 
 extern int wait_for_key_construction(struct key *key, bool intr);