KEYS: reset parent each time before searching key_user_tree

In key_user_lookup(), if there is no key_user for the given uid, we drop
key_user_lock, allocate a new key_user, and search the tree again.  But
we failed to set 'parent' to NULL at the beginning of the second search.
If the tree were to be empty for the second search, the insertion would
be done with an invalid 'parent', scribbling over freed memory.

Fortunately this can't actually happen currently because the tree always
contains at least the root_key_user.  But it still should be fixed to
make the code more robust.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>

diff --git a/security/keys/key.c b/security/keys/key.c
index e5c0896c3a8ff2b248858d6f1d1d8f9a93679d8e..eb914a838840df416f26af2c0cd73f87c60a5032 100644 (file)
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -54,10 +54,10 @@ void __key_check(const struct key *key)
 struct key_user *key_user_lookup(kuid_t uid)
 {
        struct key_user *candidate = NULL, *user;
-       struct rb_node *parent = NULL;
-       struct rb_node **p;
+       struct rb_node *parent, **p;
 
 try_again:
+       parent = NULL;
        p = &key_user_tree.rb_node;
        spin_lock(&key_user_lock);