There are several ways to remove L2TP sessions:
* deleting a session explicitly using the netlink interface (with
L2TP_CMD_SESSION_DELETE),
* deleting the session's parent tunnel (either by closing the
tunnel's file descriptor or using the netlink interface),
* closing the PPPOL2TP file descriptor of a PPP pseudo-wire.
In some cases, when these methods are used concurrently on the same
session, the session can be removed twice, leading to use-after-free
bugs.
This patch adds a 'dead' flag, used by l2tp_session_delete() and
l2tp_tunnel_closeall() to prevent them from stepping on each other's
toes.
The session deletion path used when closing a PPPOL2TP file descriptor
doesn't need to be adapted. It already has to ensure that a session
remains valid for the lifetime of its PPPOL2TP file descriptor.
So it takes an extra reference on the session in the ->session_close()
callback (pppol2tp_session_close()), which is eventually dropped
in the ->sk_destruct() callback of the PPPOL2TP socket
(pppol2tp_session_destruct()).
Still, __l2tp_session_unhash() and l2tp_session_queue_purge() can be
called twice and even concurrently for a given session, but thanks to
proper locking and re-initialisation of list fields, this is not an
issue.
Signed-off-by: Guillaume Nault <g.na...@alphalink.fr>
---
net/l2tp/l2tp_core.c | 6 ++++++
net/l2tp/l2tp_core.h | 1 +
2 files changed, 7 insertions(+)
diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index ee485df73ccd..d8c2a89a76e1 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1314,6 +1314,9 @@ void l2tp_tunnel_closeall(struct l2tp_tunnel *tunnel)
hlist_del_init(&session->hlist);
+ if (test_and_set_bit(0, &session->dead))
+ goto again;
+
if (session->ref != NULL)
(*session->ref)(session);
@@ -1750,6 +1753,9 @@ EXPORT_SYMBOL_GPL(__l2tp_session_unhash);
*/
int l2tp_session_delete(struct l2tp_session *session)
{
+ if (test_and_set_bit(0, &session->dead))
+ return 0;
+
if (session->ref)
(*session->ref)(session);
__l2tp_session_unhash(session);
diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index a305e0c5925a..70a12df40a5f 100644
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -76,6 +76,7 @@ struct l2tp_session_cfg {
struct l2tp_session {
int magic; /* should be
* L2TP_SESSION_MAGIC */
+ long dead;
struct l2tp_tunnel *tunnel; /* back pointer to tunnel
* context */
--
2.14.1
