[PATCH net 06/10] ovpn: zero-initialize sockaddr before learning a floated endpoint

[Antonio Quartulli <antonio@openvpn.net>]

ovpn_peer_endpoints_update() builds the new remote endpoint in an
on-stack struct sockaddr_storage that is left uninitialized. For IPv4
only sin_family/sin_addr/sin_port are written, leaving the 8-byte
sin_zero padding as stack garbage (for IPv6, sin6_flowinfo is left
uninitialized likewise).

ovpn_peer_reset_sockaddr() -> ovpn_bind_from_sockaddr() then memcpy()s
sizeof(struct sockaddr_in)/sizeof(struct sockaddr_in6) bytes - padding
included - into bind->remote. That buffer is later hashed with jhash()
over the same length to place the peer in the by_transp_addr table, so
the garbage padding lands the floated peer in an essentially random
bucket. Lockless lookups in ovpn_peer_get_by_transp_addr() build their
key from a zero-initialized sockaddr_storage, compute a different bucket
and fail to find the peer.

This is also a plain use of uninitialized stack memory in jhash().

Build the floated endpoint with a designated initializer so the
padding (sin_zero for IPv4, sin6_flowinfo for IPv6) is zeroed as part
of the assignment. This keeps the padding out of the by_transp_addr
hash key without memset-ing the whole sockaddr_storage on every
received packet.

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 | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ovpn/peer.c b/drivers/net/ovpn/peer.c
index a330892e82bf..33fb0a75e600 100644
--- a/drivers/net/ovpn/peer.c
+++ b/drivers/net/ovpn/peer.c
@@ -222,9 +222,16 @@ void ovpn_peer_endpoints_update(struct ovpn_peer *peer, struct sk_buff *skb)
 			 */
 			local_ip = &ip_hdr(skb)->daddr;
 			sa = (struct sockaddr_in *)&ss;
-			sa->sin_family = AF_INET;
-			sa->sin_addr.s_addr = ip_hdr(skb)->saddr;
-			sa->sin_port = udp_hdr(skb)->source;
+			/* use a designated initializer so the sin_zero padding
+			 * is zeroed (it ends up in the by_transp_addr hash key)
+			 * without memset-ing the whole sockaddr_storage on the
+			 * RX fast path
+			 */
+			*sa = (struct sockaddr_in) {
+				.sin_family = AF_INET,
+				.sin_addr.s_addr = ip_hdr(skb)->saddr,
+				.sin_port = udp_hdr(skb)->source,
+			};
 			salen = sizeof(*sa);
 			reset_cache = true;
 			break;
@@ -250,11 +257,19 @@ void ovpn_peer_endpoints_update(struct ovpn_peer *peer, struct sk_buff *skb)
 			 */
 			local_ip = &ipv6_hdr(skb)->daddr;
 			sa6 = (struct sockaddr_in6 *)&ss;
-			sa6->sin6_family = AF_INET6;
-			sa6->sin6_addr = ipv6_hdr(skb)->saddr;
-			sa6->sin6_port = udp_hdr(skb)->source;
-			sa6->sin6_scope_id = ipv6_iface_scope_id(&ipv6_hdr(skb)->saddr,
-								 skb->skb_iif);
+			/* use a designated initializer so the sin6_flowinfo
+			 * padding is zeroed (it ends up in the by_transp_addr
+			 * hash key) without memset-ing the whole
+			 * sockaddr_storage on the RX fast path
+			 */
+			*sa6 = (struct sockaddr_in6) {
+				.sin6_family = AF_INET6,
+				.sin6_addr = ipv6_hdr(skb)->saddr,
+				.sin6_port = udp_hdr(skb)->source,
+				.sin6_scope_id =
+					ipv6_iface_scope_id(&ipv6_hdr(skb)->saddr,
+							    skb->skb_iif),
+			};
 			salen = sizeof(*sa6);
 			reset_cache = true;
 			break;
-- 
2.54.0