[PATCH 7.1 274/438] fou: Fix use-after-free in fou_create()

7.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Xuanqiang Luo <[email protected]>

commit b14361aca6350ff7907b0e9903c7b94dc7d5d4a0 upstream.

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 <[email protected]>
Link: https://lore.kernel.org/netdev/[email protected]/
Cc: [email protected]
Signed-off-by: Xuanqiang Luo <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 net/ipv4/fou_core.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv4/fou_core.c
+++ b/net/ipv4/fou_core.c
@@ -629,9 +629,9 @@ static int fou_create(struct net *net, s
 	return 0;
 
 error:
-	kfree(fou);
 	if (sock)
 		udp_tunnel_sock_release(sock->sk);
+	kfree_rcu(fou, rcu);
 
 	return err;
 }