[PATCH] Don't leak a key reference if request_key() tries to use a revoked keyring

[David Jeffery <djeffery@redhat.com>]

If a request_key() call to allocate and fill out a key attempts to insert the
key structure into a revoked keyring, the key will leak, using memory and part
of the user's key quota until the system reboots. This is from a failure of
construct_alloc_key() to decrement the key's reference count after the attempt
to insert into the requested keyring is rejected.

key_put() needs to be called in the link_prealloc_failed callpath to ensure
the unused key is released.

Signed-off-by: David Jeffery <djeffery@redhat.com>

---

The basic way to trigger this is to use keyctl to revoke a session's keyring,
then do an action which will trigger request_key().  request_key() will fail
and a key will leak.


diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 0c7aea4..486ef6f 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -414,6 +414,7 @@ link_check_failed:
 
 link_prealloc_failed:
 	mutex_unlock(&user->cons_lock);
+	key_put(key);
 	kleave(" = %d [prelink]", ret);
 	return ret;