From: Gong, Sishuai sishuai@purdue.edu
[ Upstream commit 69e16d01d1de4f1249869de342915f608feb55d5 ]
l2tp_tunnel_register() registers a tunnel without fully initializing its attribute. This can allow another kernel thread running l2tp_xmit_core() to access the uninitialized data and then cause a kernel NULL pointer dereference error, as shown below.
Thread 1 Thread 2 //l2tp_tunnel_register() list_add_rcu(&tunnel->list, &pn->l2tp_tunnel_list); //pppol2tp_connect() tunnel = l2tp_tunnel_get(sock_net(sk), info.tunnel_id); // Fetch the new tunnel ... //l2tp_xmit_core() struct sock *sk = tunnel->sock; ... bh_lock_sock(sk); //Null pointer error happens tunnel->sock = sk;
Fix this bug by initializing tunnel->sock before adding the tunnel into l2tp_tunnel_list.
Reviewed-by: Cong Wang cong.wang@bytedance.com Signed-off-by: Sishuai Gong sishuai@purdue.edu Reported-by: Sishuai Gong sishuai@purdue.edu Signed-off-by: David S. Miller davem@davemloft.net Stable-dep-of: b68777d54fac ("l2tp: Serialize access to sk_user_data with sk_callback_lock") Signed-off-by: Sasha Levin sashal@kernel.org --- net/l2tp/l2tp_core.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index 561b6d67ab8b..dc8987ed08ad 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -1480,11 +1480,15 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net, tunnel->l2tp_net = net; pn = l2tp_pernet(net);
+ sk = sock->sk; + sock_hold(sk); + tunnel->sock = sk; + spin_lock_bh(&pn->l2tp_tunnel_list_lock); list_for_each_entry(tunnel_walk, &pn->l2tp_tunnel_list, list) { if (tunnel_walk->tunnel_id == tunnel->tunnel_id) { spin_unlock_bh(&pn->l2tp_tunnel_list_lock); - + sock_put(sk); ret = -EEXIST; goto err_sock; } @@ -1492,10 +1496,6 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net, list_add_rcu(&tunnel->list, &pn->l2tp_tunnel_list); spin_unlock_bh(&pn->l2tp_tunnel_list_lock);
- sk = sock->sk; - sock_hold(sk); - tunnel->sock = sk; - if (tunnel->encap == L2TP_ENCAPTYPE_UDP) { struct udp_tunnel_sock_cfg udp_cfg = { .sk_user_data = tunnel,