2022-06-10 05:26:03

by Xiaohui Zhang

Subject: [PATCH 1/1] l2tp: fix possible use-after-free

Similar to the handling of l2tp_tunnel_get in commit a622b40035d1
("l2ip: fix possible use-after-free"), we thought a patch might
be needed here as well.

Before taking a refcount on a rcu protected structure,
we need to make sure the refcount is not zero.

Signed-off-by: Xiaohui Zhang <[email protected]>
---
net/l2tp/l2tp_core.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 7499c51b1850..96e8966f900d 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -252,8 +252,8 @@ struct l2tp_session *l2tp_tunnel_get_session(struct l2tp_tunnel *tunnel,

rcu_read_lock_bh();
hlist_for_each_entry_rcu(session, session_list, hlist)
- if (session->session_id == session_id) {
- l2tp_session_inc_refcount(session);
+ if (session->session_id == session_id &&
+ refcount_inc_not_zero(&session->ref_count)) {
rcu_read_unlock_bh();

return session;
@@ -273,8 +273,8 @@ struct l2tp_session *l2tp_session_get(const struct net *net, u32 session_id)

rcu_read_lock_bh();
hlist_for_each_entry_rcu(session, session_list, global_hlist)
- if (session->session_id == session_id) {
- l2tp_session_inc_refcount(session);
+ if (session->session_id == session_id &&
+ refcount_inc_not_zero(&session->ref_count)) {
rcu_read_unlock_bh();

return session;
@@ -294,8 +294,8 @@ struct l2tp_session *l2tp_session_get_nth(struct l2tp_tunnel *tunnel, int nth)
rcu_read_lock_bh();
for (hash = 0; hash < L2TP_HASH_SIZE; hash++) {
hlist_for_each_entry_rcu(session, &tunnel->session_hlist[hash], hlist) {
- if (++count > nth) {
- l2tp_session_inc_refcount(session);
+ if (++count > nth &&
+ refcount_inc_not_zero(&session->ref_count)) {
rcu_read_unlock_bh();
return session;
}
@@ -321,8 +321,8 @@ struct l2tp_session *l2tp_session_get_by_ifname(const struct net *net,
rcu_read_lock_bh();
for (hash = 0; hash < L2TP_HASH_SIZE_2; hash++) {
hlist_for_each_entry_rcu(session, &pn->l2tp_session_hlist[hash], global_hlist) {
- if (!strcmp(session->ifname, ifname)) {
- l2tp_session_inc_refcount(session);
+ if (!strcmp(session->ifname, ifname) &&
+ refcount_inc_not_zero(&session->ref_count)) {
rcu_read_unlock_bh();

return session;
--
2.17.1

2022-06-14 09:03:18

by Paolo Abeni

Subject: Re: [PATCH 1/1] l2tp: fix possible use-after-free

On Fri, 2022-06-10 at 13:16 +0800, Xiaohui Zhang wrote:
> Similar to the handling of l2tp_tunnel_get in commit a622b40035d1
> ("l2ip: fix possible use-after-free"), we thought a patch might
> be needed here as well.
>
> Before taking a refcount on a rcu protected structure,
> we need to make sure the refcount is not zero.
>
> Signed-off-by: Xiaohui Zhang <[email protected]>

I'm sorry for the late, trivial feedback, but we need a Fixes: tag
here. Since you need to repost, please insert the target tree
explicitly into the email subj.

Thanks!

Paolo