From: Xuanqiang Luo fou_create() publishes struct fou through sk_user_data before adding the new FOU port to the per-netns list. If fou_add_to_port_list() fails, the error path frees fou while it is still reachable through sk_user_data. A concurrent receive can then dereference the freed object in fou_from_sock(). This ordering issue was previously noted in the linked discussion. The failure is reachable when local port 0 is requested. Each socket binds to a different ephemeral port, but fou_cfg_cmp() compares the requested port 0 and reports -EALREADY once an entry already exists. Release the tunnel socket before freeing fou so sk_user_data is cleared first, and defer reclamation with kfree_rcu() to protect concurrent RCU readers. This matches the lifetime handling in fou_release(). Fixes: 23461551c006 ("fou: Support for foo-over-udp RX path") Suggested-by: Kuniyuki Iwashima Link: https://lore.kernel.org/netdev/20260502031401.3557229-12-kuniyu@google.com/ Cc: stable@vger.kernel.org Signed-off-by: Xuanqiang Luo --- net/ipv4/fou_core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/ipv4/fou_core.c b/net/ipv4/fou_core.c index 865bd7205122d..ab09dfcdecbd5 100644 --- a/net/ipv4/fou_core.c +++ b/net/ipv4/fou_core.c @@ -629,9 +629,9 @@ static int fou_create(struct net *net, struct fou_cfg *cfg, return 0; error: - kfree(fou); if (sock) udp_tunnel_sock_release(sock->sk); + kfree_rcu(fou, rcu); return err; } -- 2.43.0