[PATCH ovpn net v3 2/6] ovpn: skip UDP source validation for unspecified addresses

ovpn validates the cached local UDP source address before reusing or
refreshing a peer dst cache. This is only meaningful when a concrete
source address is selected.

For IPv6, calling ipv6_chk_addr with :: checks whether the unspecified
address itself is configured on the host. A peer may legitimately have
bind->local.ipv6 set to :: when no local endpoint was configured or
after a stale learned address was cleared. In that case the source
should be left unspecified and selected by ip6_dst_lookup_flow().

For IPv4, inet_confirm_addr(..., local = 0, ...) asks for local address
autoselection rather than validating a chosen source. Skip the precheck
there as well and let ip_route_output_flow select or reject the source.

Only validate non-zero/non-any source addresses.

Fixes: 08857b5ec5d9 ("ovpn: implement basic TX path (UDP)")
Signed-off-by: Ralf Lici <[email protected]>
---
No changes since v2 https://lore.kernel.org/openvpn-devel/cb51001bfdaeba899b6ca9b22186ea2ebb49c23c.1785308184.git.ralf@mandelbit.com/

No changes since v1 https://lore.kernel.org/openvpn-devel/cb51001bfdaeba899b6ca9b22186ea2ebb49c23c.1785253480.git.ralf@mandelbit.com/

 drivers/net/ovpn/udp.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ovpn/udp.c b/drivers/net/ovpn/udp.c
index 7f69e8890b5b..df4750dabd1e 100644
--- a/drivers/net/ovpn/udp.c
+++ b/drivers/net/ovpn/udp.c
@@ -161,8 +161,8 @@ static int ovpn_udp4_output(struct ovpn_peer *peer, struct ovpn_bind *bind,
 	if (rt)
 		goto transmit;
 
-	if (unlikely(!inet_confirm_addr(sock_net(sk), NULL, 0, fl.saddr,
-					RT_SCOPE_HOST))) {
+	if (fl.saddr && unlikely(!inet_confirm_addr(sock_net(sk), NULL, 0,
+						    fl.saddr, RT_SCOPE_HOST))) {
 		/* we may end up here when the cached address is not usable
 		 * anymore. In this case we reset address/cache and perform a
 		 * new look up
@@ -238,7 +238,8 @@ static int ovpn_udp6_output(struct ovpn_peer *peer, struct ovpn_bind *bind,
 	if (dst)
 		goto transmit;
 
-	if (unlikely(!ipv6_chk_addr(sock_net(sk), &fl.saddr, NULL, 0))) {
+	if (!ipv6_addr_any(&fl.saddr) &&
+	    unlikely(!ipv6_chk_addr(sock_net(sk), &fl.saddr, NULL, 0))) {
 		/* we may end up here when the cached address is not usable
 		 * anymore. In this case we reset address/cache and perform a
 		 * new look up
-- 
2.55.0