From 0b2c59720e65885a394a017d0cf9cab118914682 Mon Sep 17 00:00:00 2001 From: Cong Wang Date: Fri, 13 Jan 2023 19:01:37 -0800 Subject: [PATCH] l2tp: close all race conditions in l2tp_tunnel_register() The code in l2tp_tunnel_register() is racy in several ways: 1. It modifies the tunnel socket _after_ publishing it. 2. It calls setup_udp_tunnel_sock() on an existing socket without locking. 3. It changes sock lock class on fly, which triggers many syzbot reports. This patch amends all of them by moving socket initialization code before publishing and under sock lock. As suggested by Jakub, the l2tp lockdep class is not necessary as we can just switch to bh_lock_sock_nested(). Fixes: 37159ef2c1ae ("l2tp: fix a lockdep splat") Fixes: 6b9f34239b00 ("l2tp: fix races in tunnel creation") Reported-by: syzbot+52866e24647f9a23403f@syzkaller.appspotmail.com Reported-by: syzbot+94cc2a66fc228b23f360@syzkaller.appspotmail.com Reported-by: Tetsuo Handa Cc: Guillaume Nault Cc: Jakub Sitnicki Cc: Eric Dumazet Cc: Tom Parkin Signed-off-by: Cong Wang Reviewed-by: Guillaume Nault Signed-off-by: David S. Miller --- net/l2tp/l2tp_core.c | 28 ++++++++++++++-------------- 1 file changed, 14 insertions(+), 14 deletions(-) diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index e9c0ce0b7972..b6554e32bb12 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -1041,7 +1041,7 @@ static int l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb, uns IPCB(skb)->flags &= ~(IPSKB_XFRM_TUNNEL_SIZE | IPSKB_XFRM_TRANSFORMED | IPSKB_REROUTED); nf_reset_ct(skb); - bh_lock_sock(sk); + bh_lock_sock_nested(sk); if (sock_owned_by_user(sk)) { kfree_skb(skb); ret = NET_XMIT_DROP; @@ -1385,8 +1385,6 @@ out: return err; } -static struct lock_class_key l2tp_socket_class; - int l2tp_tunnel_create(int fd, int version, u32 tunnel_id, u32 peer_tunnel_id, struct l2tp_tunnel_cfg *cfg, struct l2tp_tunnel **tunnelp) { @@ -1482,21 +1480,16 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net, } sk = sock->sk; + lock_sock(sk); write_lock_bh(&sk->sk_callback_lock); ret = l2tp_validate_socket(sk, net, tunnel->encap); - if (ret < 0) + if (ret < 0) { + release_sock(sk); goto err_inval_sock; + } rcu_assign_sk_user_data(sk, tunnel); write_unlock_bh(&sk->sk_callback_lock); - sock_hold(sk); - tunnel->sock = sk; - tunnel->l2tp_net = net; - - spin_lock_bh(&pn->l2tp_tunnel_idr_lock); - idr_replace(&pn->l2tp_tunnel_idr, tunnel, tunnel->tunnel_id); - spin_unlock_bh(&pn->l2tp_tunnel_idr_lock); - if (tunnel->encap == L2TP_ENCAPTYPE_UDP) { struct udp_tunnel_sock_cfg udp_cfg = { .sk_user_data = tunnel, @@ -1510,9 +1503,16 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net, tunnel->old_sk_destruct = sk->sk_destruct; sk->sk_destruct = &l2tp_tunnel_destruct; - lockdep_set_class_and_name(&sk->sk_lock.slock, &l2tp_socket_class, - "l2tp_sock"); sk->sk_allocation = GFP_ATOMIC; + release_sock(sk); + + sock_hold(sk); + tunnel->sock = sk; + tunnel->l2tp_net = net; + + spin_lock_bh(&pn->l2tp_tunnel_idr_lock); + idr_replace(&pn->l2tp_tunnel_idr, tunnel, tunnel->tunnel_id); + spin_unlock_bh(&pn->l2tp_tunnel_idr_lock); trace_register_tunnel(tunnel); -- 2.34.1