From: "Gong, Sishuai"
mainline inclusion
from mainline-v5.13-rc1
commit 69e16d01d1de4f1249869de342915f608feb55d5
category: bugfix
issue: #I3ZXZF
CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
-----------------------------------------------
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
Signed-off-by: Sishuai Gong
Reported-by: Sishuai Gong
Signed-off-by: David S. Miller
Signed-off-by: Huang Guobin
Reviewed-by: Yue Haibing
Signed-off-by: Chen Jun
Signed-off-by: Yu Changchun
---
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 203890e378cb..8eb805ee18d4 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1478,11 +1478,15 @@ 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;
}
@@ -1490,10 +1494,6 @@ 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,
--
2.22.0
