From: Cong Wang cong.wang@bytedance.com
[ Upstream commit 0b2c59720e65885a394a017d0cf9cab118914682 ]
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 penguin-kernel@I-love.SAKURA.ne.jp Cc: Guillaume Nault gnault@redhat.com Cc: Jakub Sitnicki jakub@cloudflare.com Cc: Eric Dumazet edumazet@google.com Cc: Tom Parkin tparkin@katalix.com Signed-off-by: Cong Wang cong.wang@bytedance.com Reviewed-by: Guillaume Nault gnault@redhat.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- 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 68d8b2aa6f6d..4c5227048be4 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; @@ -1387,8 +1387,6 @@ static int l2tp_tunnel_sock_create(struct net *net, 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) { @@ -1484,21 +1482,16 @@ 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, @@ -1512,9 +1505,16 @@ 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);