commit 93b4a44f3ad69520d605aace3f3486b8eb754b96
author David Howells <dhowells@redhat.com> Fri Apr 23 13:18:00 2010 -0400
committer Linus Torvalds <torvalds@linux-foundation.org> Sat Apr 24 11:31:25 2010 -0700
tree 8eb946db950ccc6aee1d00b226739f44141dd310
parent ccdb40048b2972f10bdc944913c0e0ee26b5d1f2

keys: fix an RCU warning

Fix the following RCU warning:

  ===================================================
  [ INFO: suspicious rcu_dereference_check() usage. ]
  ---------------------------------------------------
  security/keys/request_key.c:116 invoked rcu_dereference_check() without protection!

This was caused by doing:

	[root@andromeda ~]# keyctl newring fred @s
	539196288
	[root@andromeda ~]# keyctl request2 user a a 539196288
	request_key: Required key not available

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

security/keys/request_key.c

diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 03fe63e..ea97c31 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -68,7 +68,8 @@
 {
 	const struct cred *cred = current_cred();
 	key_serial_t prkey, sskey;
-	struct key *key = cons->key, *authkey = cons->authkey, *keyring;
+	struct key *key = cons->key, *authkey = cons->authkey, *keyring,
+		*session;
 	char *argv[9], *envp[3], uid_str[12], gid_str[12];
 	char key_str[12], keyring_str[3][12];
 	char desc[20];
@@ -112,10 +113,12 @@
 	if (cred->tgcred->process_keyring)
 		prkey = cred->tgcred->process_keyring->serial;
 
-	if (cred->tgcred->session_keyring)
-		sskey = rcu_dereference(cred->tgcred->session_keyring)->serial;
-	else
-		sskey = cred->user->session_keyring->serial;
+	rcu_read_lock();
+	session = rcu_dereference(cred->tgcred->session_keyring);
+	if (!session)
+		session = cred->user->session_keyring;
+	sskey = session->serial;
+	rcu_read_unlock();
 
 	sprintf(keyring_str[2], "%d", sskey);