From: Will Deacon <will@kernel.org>
To: gregkh@linuxfoundation.org
Cc: stable@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel-team@android.com, g.nault@alphalink.fr,
"David S . Miller" <davem@davemloft.net>,
Will Deacon <will@kernel.org>
Subject: [PATCH 2/2] l2tp: fix race between l2tp_session_delete() and l2tp_tunnel_closeall()
Date: Thu, 2 Apr 2020 18:31:58 +0100 [thread overview]
Message-ID: <20200402173158.7798-3-will@kernel.org> (raw)
In-Reply-To: <20200402173158.7798-1-will@kernel.org>
From: Guillaume Nault <g.nault@alphalink.fr>
commit b228a94066406b6c456321d69643b0d7ce11cfa6 upstream.
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>
Signed-off-by: Will Deacon <will@kernel.org>
---
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 394a1ddb0782..7c3da29fad8e 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1351,6 +1351,9 @@ 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);
@@ -1799,6 +1802,9 @@ 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 7cc49715606e..7c2037184b6c 100644
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -84,6 +84,7 @@ 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 */
--
2.26.0.rc2.310.g2932bb562d-goog
next prev parent reply other threads:[~2020-04-02 17:32 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-02 17:31 [PATCH 0/2] [backports] l2tp use-after-free fixes for 4.9 stable Will Deacon
2020-04-02 17:31 ` [PATCH 1/2] l2tp: ensure sessions are freed after their PPPOL2TP socket Will Deacon
2020-04-02 19:59 ` David Miller
2020-04-03 7:03 ` Will Deacon
2020-04-02 17:31 ` Will Deacon [this message]
2020-04-02 18:45 ` [PATCH 0/2] [backports] l2tp use-after-free fixes for 4.9 stable Greg KH
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