[PATCH net 1/4] ovpn: fix NULL dereference when killing missing key

[Antonio Quartulli <antonio@openvpn.net>]

From: Ralf Lici <ralf@mandelbit.com>

ovpn_crypto_kill_key assumes both crypto slots are populated and
dereferences each slot before checking it. That is not guaranteed: a
peer can have only one installed key, and the kill path may be asked to
remove a key that is not present.

Read each slot once while holding the crypto state lock, check for NULL
before looking at key_id, and only replace the slot that actually
matches.

Fixes: 89d3c0e4612a ("ovpn: kill key and notify userspace in case of IV exhaustion")
Signed-off-by: Ralf Lici <ralf@mandelbit.com>
Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
---
 drivers/net/ovpn/crypto.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ovpn/crypto.c b/drivers/net/ovpn/crypto.c
index 90580e32052f..2e95f29514fc 100644
--- a/drivers/net/ovpn/crypto.c
+++ b/drivers/net/ovpn/crypto.c
@@ -58,15 +58,19 @@ void ovpn_crypto_state_release(struct ovpn_crypto_state *cs)
 bool ovpn_crypto_kill_key(struct ovpn_crypto_state *cs, u8 key_id)
 {
 	struct ovpn_crypto_key_slot *ks = NULL;
+	struct ovpn_crypto_key_slot *tmp;
+	int slot = 0;
 
 	spin_lock_bh(&cs->lock);
-	if (rcu_access_pointer(cs->slots[0])->key_id == key_id) {
-		ks = rcu_replace_pointer(cs->slots[0], NULL,
-					 lockdep_is_held(&cs->lock));
-	} else if (rcu_access_pointer(cs->slots[1])->key_id == key_id) {
-		ks = rcu_replace_pointer(cs->slots[1], NULL,
-					 lockdep_is_held(&cs->lock));
+	tmp = rcu_access_pointer(cs->slots[slot]);
+	if (!tmp || tmp->key_id != key_id) {
+		slot = 1;
+		tmp = rcu_access_pointer(cs->slots[slot]);
 	}
+
+	if (tmp && tmp->key_id == key_id)
+		ks = rcu_replace_pointer(cs->slots[slot], NULL,
+					 lockdep_is_held(&cs->lock));
 	spin_unlock_bh(&cs->lock);
 
 	if (ks)
-- 
2.54.0