[PATCH net 07/10] ovpn: hash floated peer by transport identity only

[Antonio Quartulli <antonio@openvpn.net>]

The by_transp_addr table is keyed on the peer's remote transport
address, but the float rehash hashed bind->remote directly, while the
two other sites that touch the table build a clean key first:
ovpn_peer_add_mp() and the lookup in ovpn_peer_get_by_transp_addr()
both hash a sockaddr holding only family/address/port.

For a link-local IPv6 peer, bind->remote carries sin6_scope_id (set
from ipv6_iface_scope_id() when the endpoint is learned), and that
field is folded into the jhash() over sizeof(struct sockaddr_in6).
The lookup never sets sin6_scope_id, so after such a peer floats it is
rehashed into a scope_id-dependent bucket that lookups (scope_id 0)
never visit, making the peer unreachable through the by_transp_addr
fallback. ovpn_peer_transp_match() only compares address and port, so
the hash was keying on a field the match ignores.

sin6_scope_id must stay in bind->remote because the TX path uses it as
flowi6_oif, so it cannot just be cleared there. Instead build the hash
key from family/address/port only, exactly like ovpn_peer_add_mp() and
the lookup, so all three sites agree on the bucket.

Fixes: f0281c1d3732 ("ovpn: add support for updating local or remote UDP endpoint")
Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
---
 drivers/net/ovpn/peer.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ovpn/peer.c b/drivers/net/ovpn/peer.c
index 33fb0a75e600..eada414a9d92 100644
--- a/drivers/net/ovpn/peer.c
+++ b/drivers/net/ovpn/peer.c
@@ -904,7 +904,10 @@ bool ovpn_peer_check_by_src(struct ovpn_priv *ovpn, struct sk_buff *skb,
 static void __ovpn_peer_hash_transp_addr(struct ovpn_peer *peer,
 					 const struct ovpn_bind *bind)
 {
+	struct sockaddr_storage sa = {};
 	struct hlist_nulls_head *nhead;
+	struct sockaddr_in6 *sa6;
+	struct sockaddr_in *sa4;
 	size_t salen;
 
 	lockdep_assert_held(&peer->ovpn->lock);
@@ -920,12 +923,26 @@ static void __ovpn_peer_hash_transp_addr(struct ovpn_peer *peer,
 	if (unlikely(hlist_unhashed(&peer->hash_entry_id)))
 		return;
 
+	/* Build the hash key from the transport identity only
+	 * (family/address/port), matching ovpn_peer_add_mp() and the lookup
+	 * in ovpn_peer_get_by_transp_addr(). Hashing bind->remote directly
+	 * would fold in sin6_scope_id (set on the float path but never by the
+	 * lookup), scattering the peer into a bucket lookups cannot reach.
+	 */
 	switch (bind->remote.in4.sin_family) {
 	case AF_INET:
-		salen = sizeof(struct sockaddr_in);
+		sa4 = (struct sockaddr_in *)&sa;
+		sa4->sin_family = AF_INET;
+		sa4->sin_addr.s_addr = bind->remote.in4.sin_addr.s_addr;
+		sa4->sin_port = bind->remote.in4.sin_port;
+		salen = sizeof(*sa4);
 		break;
 	case AF_INET6:
-		salen = sizeof(struct sockaddr_in6);
+		sa6 = (struct sockaddr_in6 *)&sa;
+		sa6->sin6_family = AF_INET6;
+		sa6->sin6_addr = bind->remote.in6.sin6_addr;
+		sa6->sin6_port = bind->remote.in6.sin6_port;
+		salen = sizeof(*sa6);
 		break;
 	default:
 		return;
@@ -934,8 +951,8 @@ static void __ovpn_peer_hash_transp_addr(struct ovpn_peer *peer,
 	/* remove old hashing (no-op if entry is not currently linked) */
 	hlist_nulls_del_init_rcu(&peer->hash_entry_transp_addr);
 	/* re-add with current transport address */
-	nhead = ovpn_get_hash_head(peer->ovpn->peers->by_transp_addr,
-				   &bind->remote, salen);
+	nhead = ovpn_get_hash_head(peer->ovpn->peers->by_transp_addr, &sa,
+				   salen);
 	hlist_nulls_add_head_rcu(&peer->hash_entry_transp_addr, nhead);
 }
 
-- 
2.54.0