[PATCH ovpn net v2] ovpn: fix NULL dereference when killing missing key

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 <[email protected]>
---
Changes since v1 https://lore.kernel.org/openvpn-devel/9fc33e6f9fae10b9e372a3e06934d697edf5b024.1782829171.git.ralf@mandelbit.com/
- Remove unnecessary braces around single-statement if/else branches.

 drivers/net/ovpn/crypto.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ovpn/crypto.c b/drivers/net/ovpn/crypto.c
index 90580e32052f..8cb7078a1d93 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;
 
 	spin_lock_bh(&cs->lock);
-	if (rcu_access_pointer(cs->slots[0])->key_id == key_id) {
+	tmp = rcu_access_pointer(cs->slots[0]);
+	if (tmp && tmp->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) {
+	else
+		tmp = rcu_access_pointer(cs->slots[1]);
+
+	if (!ks && tmp && tmp->key_id == key_id)
 		ks = rcu_replace_pointer(cs->slots[1], NULL,
 					 lockdep_is_held(&cs->lock));
-	}
 	spin_unlock_bh(&cs->lock);
 
 	if (ks)

base-commit: 903db046d5579bef0ea699eae4b279dd6455fc9f
-- 
2.54.0