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ovpn: replace bind when clearing stale local source

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The UDP output fallback clears bind->local in place when the remembered
source address is no longer usable. The bind is RCU-published and read
locklessly by concurrent TX, so an IPv6 reader can observe a torn
address.

Retry the route lookup with source address autoselection without
modifying the bind. After a successful lookup, revalidate the bind and
route key under peer->lock, reset the dst cache, and best-effort publish
a replacement bind with a wildcard local address.

Do not cache the resolved dst when clearing the local source. Replacing
the source invalidates all per-CPU cache entries, while
dst_cache_set_ip4 and dst_cache_set_ip6 update only the current CPU
slot. The current packet can still use the resolved route; if bind
allocation fails, a later cache miss retries the repair.

Fixes: 08857b5ec5 ("ovpn: implement basic TX path (UDP)")
Signed-off-by: Ralf Lici <ralf@mandelbit.com>
Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
This commit is contained in:
Ralf Lici 2026-08-28 16:50:27 +02:00 committed by Antonio Quartulli
parent aea934a221
commit 7d8104988f
1 changed files with 56 additions and 25 deletions
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81
drivers/net/ovpn/udp.c
View File

@ -185,7 +185,7 @@ static void ovpn_dst_cache_check_key(struct ovpn_peer *peer,
* to detect whether the bind was replaced while the route lookup was running.
*
* Return: true if the lookup result still matches the current peer state and
* may update the dst cache.
* may update the dst cache or replace the bind.
*/
static bool ovpn_dst_cache_current(const struct ovpn_peer *peer,
const struct ovpn_bind *bind,
@ -218,6 +218,9 @@ static int ovpn_udp4_output(struct ovpn_peer *peer, struct ovpn_bind *bind,
struct sk_buff *skb,
const struct ovpn_route_key *key)
{
struct sockaddr_storage remote;
struct in_addr local = {};
bool reset_local = false;
struct rtable *rt;
struct flowi4 fl = {
.saddr = bind->local.ipv4.s_addr,
@ -236,24 +239,17 @@ static int ovpn_udp4_output(struct ovpn_peer *peer, struct ovpn_bind *bind,
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
/* The learned local address is not usable anymore.
* Retry with source address autoselection.
*/
fl.saddr = 0;
spin_lock_bh(&peer->lock);
bind->local.ipv4.s_addr = 0;
spin_unlock_bh(&peer->lock);
dst_cache_reset(cache);
reset_local = true;
}
rt = ip_route_output_flow(sock_net(sk), &fl, sk);
if (IS_ERR(rt) && PTR_ERR(rt) == -EINVAL) {
fl.saddr = 0;
spin_lock_bh(&peer->lock);
bind->local.ipv4.s_addr = 0;
spin_unlock_bh(&peer->lock);
dst_cache_reset(cache);
reset_local = true;
rt = ip_route_output_flow(sock_net(sk), &fl, sk);
}
@ -267,10 +263,28 @@ static int ovpn_udp4_output(struct ovpn_peer *peer, struct ovpn_bind *bind,
goto err;
}
/* avoid storing a stale cache */
/* avoid storing a stale cache or local address */
spin_lock_bh(&peer->lock);
if (likely(ovpn_dst_cache_current(peer, bind, key)))
dst_cache_set_ip4(cache, &rt->dst, fl.saddr);
if (likely(ovpn_dst_cache_current(peer, bind, key))) {
if (!reset_local) {
dst_cache_set_ip4(cache, &rt->dst, fl.saddr);
spin_unlock_bh(&peer->lock);
goto transmit;
}
/* invalidate per-CPU dst entries that may still carry
* the stale source
*/
dst_cache_reset(cache);
/* preserve the current remote */
memcpy(&remote, &bind->remote, sizeof(struct sockaddr_in));
/* The current packet already has a valid wildcard-source route.
* If replacing the bind fails, leave the stale local in place;
* a later cache miss will retry the repair.
*/
ovpn_peer_reset_sockaddr(peer, &remote, &local);
}
spin_unlock_bh(&peer->lock);
transmit:
@ -300,6 +314,9 @@ static int ovpn_udp6_output(struct ovpn_peer *peer, struct ovpn_bind *bind,
struct sk_buff *skb,
const struct ovpn_route_key *key)
{
struct in6_addr local = in6addr_any;
struct sockaddr_storage remote;
bool reset_local = false;
struct dst_entry *dst;
int ret;
@ -320,15 +337,11 @@ static int ovpn_udp6_output(struct ovpn_peer *peer, struct ovpn_bind *bind,
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
/* The learned local address is not usable anymore.
* Retry with source address autoselection.
*/
fl.saddr = in6addr_any;
spin_lock_bh(&peer->lock);
bind->local.ipv6 = in6addr_any;
spin_unlock_bh(&peer->lock);
dst_cache_reset(cache);
reset_local = true;
}
dst = ip6_dst_lookup_flow(sock_net(sk), sk, &fl, NULL);
@ -340,10 +353,28 @@ static int ovpn_udp6_output(struct ovpn_peer *peer, struct ovpn_bind *bind,
goto err;
}
/* avoid storing a stale cache */
/* avoid storing a stale cache or local address */
spin_lock_bh(&peer->lock);
if (likely(ovpn_dst_cache_current(peer, bind, key)))
dst_cache_set_ip6(cache, dst, &fl.saddr);
if (likely(ovpn_dst_cache_current(peer, bind, key))) {
if (!reset_local) {
dst_cache_set_ip6(cache, dst, &fl.saddr);
spin_unlock_bh(&peer->lock);
goto transmit;
}
/* invalidate per-CPU dst entries that may still carry
* the stale source
*/
dst_cache_reset(cache);
/* preserve the current remote */
memcpy(&remote, &bind->remote, sizeof(struct sockaddr_in6));
/* The current packet already has a valid wildcard-source route.
* If replacing the bind fails, leave the stale local in place;
* a later cache miss will retry the repair.
*/
ovpn_peer_reset_sockaddr(peer, &remote, &local);
}
spin_unlock_bh(&peer->lock);
transmit: