This is a note to let you know that I've just added the patch titled
net: fix a concurrency bug in l2tp_tunnel_register()
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
net-fix-a-concurrency-bug-in-l2tp_tunnel_register.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 81910e59f8971e9939e76923de503aef9e126c27
Author: Gong, Sishuai <sishuai@xxxxxxxxxx>
Date: Tue Apr 27 15:04:24 2021 +0000
net: fix a concurrency bug in l2tp_tunnel_register()
[ 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@xxxxxxxxxxxxx>
Signed-off-by: Sishuai Gong <sishuai@xxxxxxxxxx>
Reported-by: Sishuai Gong <sishuai@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Stable-dep-of: b68777d54fac ("l2tp: Serialize access to sk_user_data with sk_callback_lock")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
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,
