diff options
| author | Guillaume Nault <g.nault@alphalink.fr> | 2017-09-22 15:39:24 +0200 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2017-09-25 14:44:41 -0700 |
| commit | b228a94066406b6c456321d69643b0d7ce11cfa6 (patch) | |
| tree | bff46ce62caf374bf2bf49e8f8a8110696c2a6d2 /net | |
| parent | cdd10c9627496ad25c87ce6394e29752253c69d3 (diff) | |
l2tp: fix race between l2tp_session_delete() and l2tp_tunnel_closeall()
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.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
| -rw-r--r-- | net/l2tp/l2tp_core.c | 6 | ||||
| -rw-r--r-- | net/l2tp/l2tp_core.h | 1 |
2 files changed, 7 insertions, 0 deletions
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 @@ again: 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 */ |