KEYS: Add an RCU payload dereference macro

Add an RCU payload dereference macro as this seems to be a common piece of code
amongst key types that use RCU referenced payloads.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

include/linux/key.h

@@ -275,6 +275,10 @@ static inline key_serial_t key_serial(struct key *key)
 	return key ? key->serial : 0;
 }
 
+#define rcu_dereference_key(KEY)					\
+	(rcu_dereference_protected((KEY)->payload.rcudata,		\
+				   rwsem_is_locked(&((struct key *)(KEY))->sem)))
+
 #ifdef CONFIG_SYSCTL
 extern ctl_table key_sysctls[];
 #endif

security/keys/encrypted.c

@@ -765,8 +765,7 @@ static long encrypted_read(const struct key *key, char __user *buffer,
 	size_t asciiblob_len;
 	int ret;
 
-	epayload = rcu_dereference_protected(key->payload.data,
-				  rwsem_is_locked(&((struct key *)key)->sem));
+	epayload = rcu_dereference_key(key);
 
 	/* returns the hex encoded iv, encrypted-data, and hmac as ascii */
 	asciiblob_len = epayload->datablob_len + ivsize + 1

security/keys/trusted.c

@@ -1076,8 +1076,7 @@ static long trusted_read(const struct key *key, char __user *buffer,
 	char *bufp;
 	int i;
 
-	p = rcu_dereference_protected(key->payload.data,
-			rwsem_is_locked(&((struct key *)key)->sem));
+	p = rcu_dereference_key(key);
 	if (!p)
 		return -EINVAL;
 	if (!buffer || buflen <= 0)

security/keys/user_defined.c

@@ -184,8 +184,7 @@ long user_read(const struct key *key, char __user *buffer, size_t buflen)
 	struct user_key_payload *upayload;
 	long ret;
 
-	upayload = rcu_dereference_protected(
-		key->payload.data, rwsem_is_locked(&((struct key *)key)->sem));
+	upayload = rcu_dereference_key(key);
 	ret = upayload->datalen;
 
 	/* we can return the data as is */