[PATCH for-4.9 0/5] l2tp session lookup fixes

[PATCH for-4.9 0/5] l2tp session lookup fixes

[Amit Pundir]

Hi,

Kindly consider/review following l2tp fixes for stable 4.9.y.

This patchset fix race in l2tp sessions, avoid duplicate sessions
and probable "use after free" bugs. Here is the original submission
https://www.mail-archive.com/netdev@vger.kernel.org/msg161040.html

Cherry-picked and build tested on Linux 4.9.34 for
ARCH=x86/x86_64 + allmodconfig.

Regards,
Amit Pundir


Guillaume Nault (5):
  l2tp: fix race in l2tp_recv_common()
  l2tp: ensure session can't get removed during pppol2tp_session_ioctl()
  l2tp: fix duplicate session creation
  l2tp: hold session while sending creation notifications
  l2tp: take a reference on sessions used in genetlink handlers

 net/l2tp/l2tp_core.c    | 152 ++++++++++++++++++++++++++++++++++++++----------
 net/l2tp/l2tp_core.h    |   6 +-
 net/l2tp/l2tp_eth.c     |  10 +---
 net/l2tp/l2tp_ip.c      |  17 ++++--
 net/l2tp/l2tp_ip6.c     |  18 ++++--
 net/l2tp/l2tp_netlink.c |  45 +++++++++-----
 net/l2tp/l2tp_ppp.c     |  75 +++++++++++++-----------
 7 files changed, 222 insertions(+), 101 deletions(-)

-- 
2.7.4

[PATCH for-4.9 1/5] l2tp: fix race in l2tp_recv_common()

[Amit Pundir]

From: Guillaume Nault <g.nault@alphalink.fr>

commit 61b9a047729bb230978178bca6729689d0c50ca2 upstream.

Taking a reference on sessions in l2tp_recv_common() is racy; this
has to be done by the callers.

To this end, a new function is required (l2tp_session_get()) to
atomically lookup a session and take a reference on it. Callers then
have to manually drop this reference.

Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
---
 net/l2tp/l2tp_core.c | 73 ++++++++++++++++++++++++++++++++++++++++++----------
 net/l2tp/l2tp_core.h |  3 +++
 net/l2tp/l2tp_ip.c   | 17 ++++++++----
 net/l2tp/l2tp_ip6.c  | 18 +++++++++----
 4 files changed, 88 insertions(+), 23 deletions(-)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index e702cb95b89b..046a5ba0ebd2 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -278,6 +278,55 @@ struct l2tp_session *l2tp_session_find(struct net *net, struct l2tp_tunnel *tunn
 }
 EXPORT_SYMBOL_GPL(l2tp_session_find);
 
+/* Like l2tp_session_find() but takes a reference on the returned session.
+ * Optionally calls session->ref() too if do_ref is true.
+ */
+struct l2tp_session *l2tp_session_get(struct net *net,
+				      struct l2tp_tunnel *tunnel,
+				      u32 session_id, bool do_ref)
+{
+	struct hlist_head *session_list;
+	struct l2tp_session *session;
+
+	if (!tunnel) {
+		struct l2tp_net *pn = l2tp_pernet(net);
+
+		session_list = l2tp_session_id_hash_2(pn, 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 (do_ref && session->ref)
+					session->ref(session);
+				rcu_read_unlock_bh();
+
+				return session;
+			}
+		}
+		rcu_read_unlock_bh();
+
+		return NULL;
+	}
+
+	session_list = l2tp_session_id_hash(tunnel, session_id);
+	read_lock_bh(&tunnel->hlist_lock);
+	hlist_for_each_entry(session, session_list, hlist) {
+		if (session->session_id == session_id) {
+			l2tp_session_inc_refcount(session);
+			if (do_ref && session->ref)
+				session->ref(session);
+			read_unlock_bh(&tunnel->hlist_lock);
+
+			return session;
+		}
+	}
+	read_unlock_bh(&tunnel->hlist_lock);
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(l2tp_session_get);
+
 struct l2tp_session *l2tp_session_get_nth(struct l2tp_tunnel *tunnel, int nth,
 					  bool do_ref)
 {
@@ -637,6 +686,9 @@ static int l2tp_recv_data_seq(struct l2tp_session *session, struct sk_buff *skb)
  * a data (not control) frame before coming here. Fields up to the
  * session-id have already been parsed and ptr points to the data
  * after the session-id.
+ *
+ * session->ref() must have been called prior to l2tp_recv_common().
+ * session->deref() will be called automatically after skb is processed.
  */
 void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
 		      unsigned char *ptr, unsigned char *optr, u16 hdrflags,
@@ -646,14 +698,6 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
 	int offset;
 	u32 ns, nr;
 
-	/* The ref count is increased since we now hold a pointer to
-	 * the session. Take care to decrement the refcnt when exiting
-	 * this function from now on...
-	 */
-	l2tp_session_inc_refcount(session);
-	if (session->ref)
-		(*session->ref)(session);
-
 	/* Parse and check optional cookie */
 	if (session->peer_cookie_len > 0) {
 		if (memcmp(ptr, &session->peer_cookie[0], session->peer_cookie_len)) {
@@ -806,8 +850,6 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
 	/* Try to dequeue as many skbs from reorder_q as we can. */
 	l2tp_recv_dequeue(session);
 
-	l2tp_session_dec_refcount(session);
-
 	return;
 
 discard:
@@ -816,8 +858,6 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
 
 	if (session->deref)
 		(*session->deref)(session);
-
-	l2tp_session_dec_refcount(session);
 }
 EXPORT_SYMBOL(l2tp_recv_common);
 
@@ -924,8 +964,14 @@ static int l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb,
 	}
 
 	/* Find the session context */
-	session = l2tp_session_find(tunnel->l2tp_net, tunnel, session_id);
+	session = l2tp_session_get(tunnel->l2tp_net, tunnel, session_id, true);
 	if (!session || !session->recv_skb) {
+		if (session) {
+			if (session->deref)
+				session->deref(session);
+			l2tp_session_dec_refcount(session);
+		}
+
 		/* Not found? Pass to userspace to deal with */
 		l2tp_info(tunnel, L2TP_MSG_DATA,
 			  "%s: no session found (%u/%u). Passing up.\n",
@@ -934,6 +980,7 @@ static int l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb,
 	}
 
 	l2tp_recv_common(session, skb, ptr, optr, hdrflags, length, payload_hook);
+	l2tp_session_dec_refcount(session);
 
 	return 0;
 
diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index e7233bad65e0..1d020505bf06 100644
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -240,6 +240,9 @@ static inline struct l2tp_tunnel *l2tp_sock_to_tunnel(struct sock *sk)
 	return tunnel;
 }
 
+struct l2tp_session *l2tp_session_get(struct net *net,
+				      struct l2tp_tunnel *tunnel,
+				      u32 session_id, bool do_ref);
 struct l2tp_session *l2tp_session_find(struct net *net,
 				       struct l2tp_tunnel *tunnel,
 				       u32 session_id);
diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
index 20669537816e..3468d5635d0a 100644
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -143,19 +143,19 @@ static int l2tp_ip_recv(struct sk_buff *skb)
 	}
 
 	/* Ok, this is a data packet. Lookup the session. */
-	session = l2tp_session_find(net, NULL, session_id);
-	if (session == NULL)
+	session = l2tp_session_get(net, NULL, session_id, true);
+	if (!session)
 		goto discard;
 
 	tunnel = session->tunnel;
-	if (tunnel == NULL)
-		goto discard;
+	if (!tunnel)
+		goto discard_sess;
 
 	/* Trace packet contents, if enabled */
 	if (tunnel->debug & L2TP_MSG_DATA) {
 		length = min(32u, skb->len);
 		if (!pskb_may_pull(skb, length))
-			goto discard;
+			goto discard_sess;
 
 		/* Point to L2TP header */
 		optr = ptr = skb->data;
@@ -165,6 +165,7 @@ static int l2tp_ip_recv(struct sk_buff *skb)
 	}
 
 	l2tp_recv_common(session, skb, ptr, optr, 0, skb->len, tunnel->recv_payload_hook);
+	l2tp_session_dec_refcount(session);
 
 	return 0;
 
@@ -203,6 +204,12 @@ static int l2tp_ip_recv(struct sk_buff *skb)
 
 	return sk_receive_skb(sk, skb, 1);
 
+discard_sess:
+	if (session->deref)
+		session->deref(session);
+	l2tp_session_dec_refcount(session);
+	goto discard;
+
 discard_put:
 	sock_put(sk);
 
diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c
index a4b0c9232bf1..b10abef6b0a0 100644
--- a/net/l2tp/l2tp_ip6.c
+++ b/net/l2tp/l2tp_ip6.c
@@ -156,19 +156,19 @@ static int l2tp_ip6_recv(struct sk_buff *skb)
 	}
 
 	/* Ok, this is a data packet. Lookup the session. */
-	session = l2tp_session_find(net, NULL, session_id);
-	if (session == NULL)
+	session = l2tp_session_get(net, NULL, session_id, true);
+	if (!session)
 		goto discard;
 
 	tunnel = session->tunnel;
-	if (tunnel == NULL)
-		goto discard;
+	if (!tunnel)
+		goto discard_sess;
 
 	/* Trace packet contents, if enabled */
 	if (tunnel->debug & L2TP_MSG_DATA) {
 		length = min(32u, skb->len);
 		if (!pskb_may_pull(skb, length))
-			goto discard;
+			goto discard_sess;
 
 		/* Point to L2TP header */
 		optr = ptr = skb->data;
@@ -179,6 +179,8 @@ static int l2tp_ip6_recv(struct sk_buff *skb)
 
 	l2tp_recv_common(session, skb, ptr, optr, 0, skb->len,
 			 tunnel->recv_payload_hook);
+	l2tp_session_dec_refcount(session);
+
 	return 0;
 
 pass_up:
@@ -216,6 +218,12 @@ static int l2tp_ip6_recv(struct sk_buff *skb)
 
 	return sk_receive_skb(sk, skb, 1);
 
+discard_sess:
+	if (session->deref)
+		session->deref(session);
+	l2tp_session_dec_refcount(session);
+	goto discard;
+
 discard_put:
 	sock_put(sk);
 
-- 
2.7.4

[PATCH for-4.9 2/5] l2tp: ensure session can't get removed during pppol2tp_session_ioctl()

[Amit Pundir]

From: Guillaume Nault <g.nault@alphalink.fr>

commit 57377d63547861919ee634b845c7caa38de4a452 upstream.

Holding a reference on session is required before calling
pppol2tp_session_ioctl(). The session could get freed while processing the
ioctl otherwise. Since pppol2tp_session_ioctl() uses the session's socket,
we also need to take a reference on it in l2tp_session_get().

Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
---
 net/l2tp/l2tp_ppp.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index 1387f547a09e..c1c9a9e08d08 100644
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -1141,11 +1141,18 @@ static int pppol2tp_tunnel_ioctl(struct l2tp_tunnel *tunnel,
 		if (stats.session_id != 0) {
 			/* resend to session ioctl handler */
 			struct l2tp_session *session =
-				l2tp_session_find(sock_net(sk), tunnel, stats.session_id);
-			if (session != NULL)
-				err = pppol2tp_session_ioctl(session, cmd, arg);
-			else
+				l2tp_session_get(sock_net(sk), tunnel,
+						 stats.session_id, true);
+
+			if (session) {
+				err = pppol2tp_session_ioctl(session, cmd,
+							     arg);
+				if (session->deref)
+					session->deref(session);
+				l2tp_session_dec_refcount(session);
+			} else {
 				err = -EBADR;
+			}
 			break;
 		}
 #ifdef CONFIG_XFRM
-- 
2.7.4

[PATCH for-4.9 3/5] l2tp: fix duplicate session creation

[Amit Pundir]

From: Guillaume Nault <g.nault@alphalink.fr>

commit dbdbc73b44782e22b3b4b6e8b51e7a3d245f3086 upstream.

l2tp_session_create() relies on its caller for checking for duplicate
sessions. This is racy since a session can be concurrently inserted
after the caller's verification.

Fix this by letting l2tp_session_create() verify sessions uniqueness
upon insertion. Callers need to be adapted to check for
l2tp_session_create()'s return code instead of calling
l2tp_session_find().

pppol2tp_connect() is a bit special because it has to work on existing
sessions (if they're not connected) or to create a new session if none
is found. When acting on a preexisting session, a reference must be
held or it could go away on us. So we have to use l2tp_session_get()
instead of l2tp_session_find() and drop the reference before exiting.

Fixes: d9e31d17ceba ("l2tp: Add L2TP ethernet pseudowire support")
Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
---
 net/l2tp/l2tp_core.c | 70 +++++++++++++++++++++++++++++++++++++++-------------
 net/l2tp/l2tp_eth.c  | 10 ++------
 net/l2tp/l2tp_ppp.c  | 60 ++++++++++++++++++++++----------------------
 3 files changed, 84 insertions(+), 56 deletions(-)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 046a5ba0ebd2..f29911ab3b80 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -378,6 +378,48 @@ struct l2tp_session *l2tp_session_find_by_ifname(struct net *net, char *ifname)
 }
 EXPORT_SYMBOL_GPL(l2tp_session_find_by_ifname);
 
+static int l2tp_session_add_to_tunnel(struct l2tp_tunnel *tunnel,
+				      struct l2tp_session *session)
+{
+	struct l2tp_session *session_walk;
+	struct hlist_head *g_head;
+	struct hlist_head *head;
+	struct l2tp_net *pn;
+
+	head = l2tp_session_id_hash(tunnel, session->session_id);
+
+	write_lock_bh(&tunnel->hlist_lock);
+	hlist_for_each_entry(session_walk, head, hlist)
+		if (session_walk->session_id == session->session_id)
+			goto exist;
+
+	if (tunnel->version == L2TP_HDR_VER_3) {
+		pn = l2tp_pernet(tunnel->l2tp_net);
+		g_head = l2tp_session_id_hash_2(l2tp_pernet(tunnel->l2tp_net),
+						session->session_id);
+
+		spin_lock_bh(&pn->l2tp_session_hlist_lock);
+		hlist_for_each_entry(session_walk, g_head, global_hlist)
+			if (session_walk->session_id == session->session_id)
+				goto exist_glob;
+
+		hlist_add_head_rcu(&session->global_hlist, g_head);
+		spin_unlock_bh(&pn->l2tp_session_hlist_lock);
+	}
+
+	hlist_add_head(&session->hlist, head);
+	write_unlock_bh(&tunnel->hlist_lock);
+
+	return 0;
+
+exist_glob:
+	spin_unlock_bh(&pn->l2tp_session_hlist_lock);
+exist:
+	write_unlock_bh(&tunnel->hlist_lock);
+
+	return -EEXIST;
+}
+
 /* Lookup a tunnel by id
  */
 struct l2tp_tunnel *l2tp_tunnel_find(struct net *net, u32 tunnel_id)
@@ -1787,6 +1829,7 @@ EXPORT_SYMBOL_GPL(l2tp_session_set_header_len);
 struct l2tp_session *l2tp_session_create(int priv_size, struct l2tp_tunnel *tunnel, u32 session_id, u32 peer_session_id, struct l2tp_session_cfg *cfg)
 {
 	struct l2tp_session *session;
+	int err;
 
 	session = kzalloc(sizeof(struct l2tp_session) + priv_size, GFP_KERNEL);
 	if (session != NULL) {
@@ -1842,6 +1885,13 @@ struct l2tp_session *l2tp_session_create(int priv_size, struct l2tp_tunnel *tunn
 
 		l2tp_session_set_header_len(session, tunnel->version);
 
+		err = l2tp_session_add_to_tunnel(tunnel, session);
+		if (err) {
+			kfree(session);
+
+			return ERR_PTR(err);
+		}
+
 		/* Bump the reference count. The session context is deleted
 		 * only when this drops to zero.
 		 */
@@ -1851,28 +1901,14 @@ struct l2tp_session *l2tp_session_create(int priv_size, struct l2tp_tunnel *tunn
 		/* Ensure tunnel socket isn't deleted */
 		sock_hold(tunnel->sock);
 
-		/* Add session to the tunnel's hash list */
-		write_lock_bh(&tunnel->hlist_lock);
-		hlist_add_head(&session->hlist,
-			       l2tp_session_id_hash(tunnel, session_id));
-		write_unlock_bh(&tunnel->hlist_lock);
-
-		/* And to the global session list if L2TPv3 */
-		if (tunnel->version != L2TP_HDR_VER_2) {
-			struct l2tp_net *pn = l2tp_pernet(tunnel->l2tp_net);
-
-			spin_lock_bh(&pn->l2tp_session_hlist_lock);
-			hlist_add_head_rcu(&session->global_hlist,
-					   l2tp_session_id_hash_2(pn, session_id));
-			spin_unlock_bh(&pn->l2tp_session_hlist_lock);
-		}
-
 		/* Ignore management session in session count value */
 		if (session->session_id != 0)
 			atomic_inc(&l2tp_session_count);
+
+		return session;
 	}
 
-	return session;
+	return ERR_PTR(-ENOMEM);
 }
 EXPORT_SYMBOL_GPL(l2tp_session_create);
 
diff --git a/net/l2tp/l2tp_eth.c b/net/l2tp/l2tp_eth.c
index 965f7e344cef..eecc64e138de 100644
--- a/net/l2tp/l2tp_eth.c
+++ b/net/l2tp/l2tp_eth.c
@@ -223,12 +223,6 @@ static int l2tp_eth_create(struct net *net, u32 tunnel_id, u32 session_id, u32 p
 		goto out;
 	}
 
-	session = l2tp_session_find(net, tunnel, session_id);
-	if (session) {
-		rc = -EEXIST;
-		goto out;
-	}
-
 	if (cfg->ifname) {
 		dev = dev_get_by_name(net, cfg->ifname);
 		if (dev) {
@@ -242,8 +236,8 @@ static int l2tp_eth_create(struct net *net, u32 tunnel_id, u32 session_id, u32 p
 
 	session = l2tp_session_create(sizeof(*spriv), tunnel, session_id,
 				      peer_session_id, cfg);
-	if (!session) {
-		rc = -ENOMEM;
+	if (IS_ERR(session)) {
+		rc = PTR_ERR(session);
 		goto out;
 	}
 
diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index c1c9a9e08d08..1696f1fd5877 100644
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -583,6 +583,7 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
 	int error = 0;
 	u32 tunnel_id, peer_tunnel_id;
 	u32 session_id, peer_session_id;
+	bool drop_refcnt = false;
 	int ver = 2;
 	int fd;
 
@@ -684,36 +685,36 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
 	if (tunnel->peer_tunnel_id == 0)
 		tunnel->peer_tunnel_id = peer_tunnel_id;
 
-	/* Create session if it doesn't already exist. We handle the
-	 * case where a session was previously created by the netlink
-	 * interface by checking that the session doesn't already have
-	 * a socket and its tunnel socket are what we expect. If any
-	 * of those checks fail, return EEXIST to the caller.
-	 */
-	session = l2tp_session_find(sock_net(sk), tunnel, session_id);
-	if (session == NULL) {
-		/* Default MTU must allow space for UDP/L2TP/PPP
-		 * headers.
+	session = l2tp_session_get(sock_net(sk), tunnel, session_id, false);
+	if (session) {
+		drop_refcnt = true;
+		ps = l2tp_session_priv(session);
+
+		/* Using a pre-existing session is fine as long as it hasn't
+		 * been connected yet.
 		 */
-		cfg.mtu = cfg.mru = 1500 - PPPOL2TP_HEADER_OVERHEAD;
+		if (ps->sock) {
+			error = -EEXIST;
+			goto end;
+		}
 
-		/* Allocate and initialize a new session context. */
-		session = l2tp_session_create(sizeof(struct pppol2tp_session),
-					      tunnel, session_id,
-					      peer_session_id, &cfg);
-		if (session == NULL) {
-			error = -ENOMEM;
+		/* consistency checks */
+		if (ps->tunnel_sock != tunnel->sock) {
+			error = -EEXIST;
 			goto end;
 		}
 	} else {
-		ps = l2tp_session_priv(session);
-		error = -EEXIST;
-		if (ps->sock != NULL)
-			goto end;
+		/* Default MTU must allow space for UDP/L2TP/PPP headers */
+		cfg.mtu = 1500 - PPPOL2TP_HEADER_OVERHEAD;
+		cfg.mru = cfg.mtu;
 
-		/* consistency checks */
-		if (ps->tunnel_sock != tunnel->sock)
+		session = l2tp_session_create(sizeof(struct pppol2tp_session),
+					      tunnel, session_id,
+					      peer_session_id, &cfg);
+		if (IS_ERR(session)) {
+			error = PTR_ERR(session);
 			goto end;
+		}
 	}
 
 	/* Associate session with its PPPoL2TP socket */
@@ -778,6 +779,8 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
 		  session->name);
 
 end:
+	if (drop_refcnt)
+		l2tp_session_dec_refcount(session);
 	release_sock(sk);
 
 	return error;
@@ -805,12 +808,6 @@ static int pppol2tp_session_create(struct net *net, u32 tunnel_id, u32 session_i
 	if (tunnel->sock == NULL)
 		goto out;
 
-	/* Check that this session doesn't already exist */
-	error = -EEXIST;
-	session = l2tp_session_find(net, tunnel, session_id);
-	if (session != NULL)
-		goto out;
-
 	/* Default MTU values. */
 	if (cfg->mtu == 0)
 		cfg->mtu = 1500 - PPPOL2TP_HEADER_OVERHEAD;
@@ -818,12 +815,13 @@ static int pppol2tp_session_create(struct net *net, u32 tunnel_id, u32 session_i
 		cfg->mru = cfg->mtu;
 
 	/* Allocate and initialize a new session context. */
-	error = -ENOMEM;
 	session = l2tp_session_create(sizeof(struct pppol2tp_session),
 				      tunnel, session_id,
 				      peer_session_id, cfg);
-	if (session == NULL)
+	if (IS_ERR(session)) {
+		error = PTR_ERR(session);
 		goto out;
+	}
 
 	ps = l2tp_session_priv(session);
 	ps->tunnel_sock = tunnel->sock;
-- 
2.7.4

[PATCH for-4.9 4/5] l2tp: hold session while sending creation notifications

[Amit Pundir]

From: Guillaume Nault <g.nault@alphalink.fr>

commit 5e6a9e5a3554a5b3db09cdc22253af1849c65dff upstream.

l2tp_session_find() doesn't take any reference on the returned session.
Therefore, the session may disappear while sending the notification.

Use l2tp_session_get() instead and decrement session's refcount once
the notification is sent.

Fixes: 33f72e6f0c67 ("l2tp : multicast notification to the registered listeners")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
---
 net/l2tp/l2tp_netlink.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/l2tp/l2tp_netlink.c b/net/l2tp/l2tp_netlink.c
index 9f66272b163b..8c0f48350027 100644
--- a/net/l2tp/l2tp_netlink.c
+++ b/net/l2tp/l2tp_netlink.c
@@ -634,10 +634,12 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
 			session_id, peer_session_id, &cfg);
 
 	if (ret >= 0) {
-		session = l2tp_session_find(net, tunnel, session_id);
-		if (session)
+		session = l2tp_session_get(net, tunnel, session_id, false);
+		if (session) {
 			ret = l2tp_session_notify(&l2tp_nl_family, info, session,
 						  L2TP_CMD_SESSION_CREATE);
+			l2tp_session_dec_refcount(session);
+		}
 	}
 
 out:
-- 
2.7.4

[PATCH for-4.9 5/5] l2tp: take a reference on sessions used in genetlink handlers

[Amit Pundir]

From: Guillaume Nault <g.nault@alphalink.fr>

commit 2777e2ab5a9cf2b4524486c6db1517a6ded25261 upstream.

Callers of l2tp_nl_session_find() need to hold a reference on the
returned session since there's no guarantee that it isn't going to
disappear from under them.

Relying on the fact that no l2tp netlink message may be processed
concurrently isn't enough: sessions can be deleted by other means
(e.g. by closing the PPPOL2TP socket of a ppp pseudowire).

l2tp_nl_cmd_session_delete() is a bit special: it runs a callback
function that may require a previous call to session->ref(). In
particular, for ppp pseudowires, the callback is l2tp_session_delete(),
which then calls pppol2tp_session_close() and dereferences the PPPOL2TP
socket. The socket might already be gone at the moment
l2tp_session_delete() calls session->ref(), so we need to take a
reference during the session lookup. So we need to pass the do_ref
variable down to l2tp_session_get() and l2tp_session_get_by_ifname().

Since all callers have to be updated, l2tp_session_find_by_ifname() and
l2tp_nl_session_find() are renamed to reflect their new behaviour.

Fixes: 309795f4bec2 ("l2tp: Add netlink control API for L2TP")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
---
 net/l2tp/l2tp_core.c    |  9 +++++++--
 net/l2tp/l2tp_core.h    |  3 ++-
 net/l2tp/l2tp_netlink.c | 39 ++++++++++++++++++++++++++-------------
 3 files changed, 35 insertions(+), 16 deletions(-)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index f29911ab3b80..3bce65183c95 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -356,7 +356,8 @@ EXPORT_SYMBOL_GPL(l2tp_session_get_nth);
 /* Lookup a session by interface name.
  * This is very inefficient but is only used by management interfaces.
  */
-struct l2tp_session *l2tp_session_find_by_ifname(struct net *net, char *ifname)
+struct l2tp_session *l2tp_session_get_by_ifname(struct net *net, char *ifname,
+						bool do_ref)
 {
 	struct l2tp_net *pn = l2tp_pernet(net);
 	int hash;
@@ -366,7 +367,11 @@ struct l2tp_session *l2tp_session_find_by_ifname(struct net *net, char *ifname)
 	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 (do_ref && session->ref)
+					session->ref(session);
 				rcu_read_unlock_bh();
+
 				return session;
 			}
 		}
@@ -376,7 +381,7 @@ struct l2tp_session *l2tp_session_find_by_ifname(struct net *net, char *ifname)
 
 	return NULL;
 }
-EXPORT_SYMBOL_GPL(l2tp_session_find_by_ifname);
+EXPORT_SYMBOL_GPL(l2tp_session_get_by_ifname);
 
 static int l2tp_session_add_to_tunnel(struct l2tp_tunnel *tunnel,
 				      struct l2tp_session *session)
diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index 1d020505bf06..0095012509ac 100644
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -248,7 +248,8 @@ struct l2tp_session *l2tp_session_find(struct net *net,
 				       u32 session_id);
 struct l2tp_session *l2tp_session_get_nth(struct l2tp_tunnel *tunnel, int nth,
 					  bool do_ref);
-struct l2tp_session *l2tp_session_find_by_ifname(struct net *net, char *ifname);
+struct l2tp_session *l2tp_session_get_by_ifname(struct net *net, char *ifname,
+						bool do_ref);
 struct l2tp_tunnel *l2tp_tunnel_find(struct net *net, u32 tunnel_id);
 struct l2tp_tunnel *l2tp_tunnel_find_nth(struct net *net, int nth);
 
diff --git a/net/l2tp/l2tp_netlink.c b/net/l2tp/l2tp_netlink.c
index 8c0f48350027..1ccd310d01a5 100644
--- a/net/l2tp/l2tp_netlink.c
+++ b/net/l2tp/l2tp_netlink.c
@@ -55,7 +55,8 @@ static int l2tp_nl_session_send(struct sk_buff *skb, u32 portid, u32 seq,
 /* Accessed under genl lock */
 static const struct l2tp_nl_cmd_ops *l2tp_nl_cmd_ops[__L2TP_PWTYPE_MAX];
 
-static struct l2tp_session *l2tp_nl_session_find(struct genl_info *info)
+static struct l2tp_session *l2tp_nl_session_get(struct genl_info *info,
+						bool do_ref)
 {
 	u32 tunnel_id;
 	u32 session_id;
@@ -66,14 +67,15 @@ static struct l2tp_session *l2tp_nl_session_find(struct genl_info *info)
 
 	if (info->attrs[L2TP_ATTR_IFNAME]) {
 		ifname = nla_data(info->attrs[L2TP_ATTR_IFNAME]);
-		session = l2tp_session_find_by_ifname(net, ifname);
+		session = l2tp_session_get_by_ifname(net, ifname, do_ref);
 	} else if ((info->attrs[L2TP_ATTR_SESSION_ID]) &&
 		   (info->attrs[L2TP_ATTR_CONN_ID])) {
 		tunnel_id = nla_get_u32(info->attrs[L2TP_ATTR_CONN_ID]);
 		session_id = nla_get_u32(info->attrs[L2TP_ATTR_SESSION_ID]);
 		tunnel = l2tp_tunnel_find(net, tunnel_id);
 		if (tunnel)
-			session = l2tp_session_find(net, tunnel, session_id);
+			session = l2tp_session_get(net, tunnel, session_id,
+						   do_ref);
 	}
 
 	return session;
@@ -652,7 +654,7 @@ static int l2tp_nl_cmd_session_delete(struct sk_buff *skb, struct genl_info *inf
 	struct l2tp_session *session;
 	u16 pw_type;
 
-	session = l2tp_nl_session_find(info);
+	session = l2tp_nl_session_get(info, true);
 	if (session == NULL) {
 		ret = -ENODEV;
 		goto out;
@@ -666,6 +668,10 @@ static int l2tp_nl_cmd_session_delete(struct sk_buff *skb, struct genl_info *inf
 		if (l2tp_nl_cmd_ops[pw_type] && l2tp_nl_cmd_ops[pw_type]->session_delete)
 			ret = (*l2tp_nl_cmd_ops[pw_type]->session_delete)(session);
 
+	if (session->deref)
+		session->deref(session);
+	l2tp_session_dec_refcount(session);
+
 out:
 	return ret;
 }
@@ -675,7 +681,7 @@ static int l2tp_nl_cmd_session_modify(struct sk_buff *skb, struct genl_info *inf
 	int ret = 0;
 	struct l2tp_session *session;
 
-	session = l2tp_nl_session_find(info);
+	session = l2tp_nl_session_get(info, false);
 	if (session == NULL) {
 		ret = -ENODEV;
 		goto out;
@@ -710,6 +716,8 @@ static int l2tp_nl_cmd_session_modify(struct sk_buff *skb, struct genl_info *inf
 	ret = l2tp_session_notify(&l2tp_nl_family, info,
 				  session, L2TP_CMD_SESSION_MODIFY);
 
+	l2tp_session_dec_refcount(session);
+
 out:
 	return ret;
 }
@@ -805,29 +813,34 @@ static int l2tp_nl_cmd_session_get(struct sk_buff *skb, struct genl_info *info)
 	struct sk_buff *msg;
 	int ret;
 
-	session = l2tp_nl_session_find(info);
+	session = l2tp_nl_session_get(info, false);
 	if (session == NULL) {
 		ret = -ENODEV;
-		goto out;
+		goto err;
 	}
 
 	msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
 	if (!msg) {
 		ret = -ENOMEM;
-		goto out;
+		goto err_ref;
 	}
 
 	ret = l2tp_nl_session_send(msg, info->snd_portid, info->snd_seq,
 				   0, session, L2TP_CMD_SESSION_GET);
 	if (ret < 0)
-		goto err_out;
+		goto err_ref_msg;
 
-	return genlmsg_unicast(genl_info_net(info), msg, info->snd_portid);
+	ret = genlmsg_unicast(genl_info_net(info), msg, info->snd_portid);
 
-err_out:
-	nlmsg_free(msg);
+	l2tp_session_dec_refcount(session);
 
-out:
+	return ret;
+
+err_ref_msg:
+	nlmsg_free(msg);
+err_ref:
+	l2tp_session_dec_refcount(session);
+err:
 	return ret;
 }
 
-- 
2.7.4

Re: [PATCH for-4.9 0/5] l2tp session lookup fixes

[Guillaume Nault]

On Mon, Jun 26, 2017 at 09:17:14PM +0530, Amit Pundir wrote:
> Hi,
> 
> Kindly consider/review following l2tp fixes for stable 4.9.y.
> 
> This patchset fix race in l2tp sessions, avoid duplicate sessions
> and probable "use after free" bugs. Here is the original submission
> https://www.mail-archive.com/netdev@vger.kernel.org/msg161040.html
> 
> Cherry-picked and build tested on Linux 4.9.34 for
> ARCH=x86/x86_64 + allmodconfig.
> 
Looks good to me. Thanks.

Re: [PATCH for-4.9 0/5] l2tp session lookup fixes

[Greg KH]

On Mon, Jun 26, 2017 at 09:17:14PM +0530, Amit Pundir wrote:
> Hi,
> 
> Kindly consider/review following l2tp fixes for stable 4.9.y.
> 
> This patchset fix race in l2tp sessions, avoid duplicate sessions
> and probable "use after free" bugs. Here is the original submission
> https://www.mail-archive.com/netdev@vger.kernel.org/msg161040.html
> 
> Cherry-picked and build tested on Linux 4.9.34 for
> ARCH=x86/x86_64 + allmodconfig.

Thanks for these, should they also go into 4.4 and older kernels?  If
so, care to make up patches for them?

thanks,

greg k-h

Re: [PATCH for-4.9 0/5] l2tp session lookup fixes

[Amit Pundir]

On 3 July 2017 at 14:18, Greg KH <gregkh@linuxfoundation.org> wrote:
> On Mon, Jun 26, 2017 at 09:17:14PM +0530, Amit Pundir wrote:
>> Hi,
>>
>> Kindly consider/review following l2tp fixes for stable 4.9.y.
>>
>> This patchset fix race in l2tp sessions, avoid duplicate sessions
>> and probable "use after free" bugs. Here is the original submission
>> https://www.mail-archive.com/netdev@vger.kernel.org/msg161040.html
>>
>> Cherry-picked and build tested on Linux 4.9.34 for
>> ARCH=x86/x86_64 + allmodconfig.
>
> Thanks for these, should they also go into 4.4 and older kernels?  If
> so, care to make up patches for them?

Tried on 4.4 but one or more net-namespace patches are missing in
between. So I was not sure if I should pull them and other dependent
patches (if any) into this patchset.

Regards,
Amit Pundir

>
> thanks,
>
> greg k-h

Re: [PATCH for-4.9 0/5] l2tp session lookup fixes

[Greg KH]

On Mon, Jul 03, 2017 at 02:26:11PM +0530, Amit Pundir wrote:
> On 3 July 2017 at 14:18, Greg KH <gregkh@linuxfoundation.org> wrote:
> > On Mon, Jun 26, 2017 at 09:17:14PM +0530, Amit Pundir wrote:
> >> Hi,
> >>
> >> Kindly consider/review following l2tp fixes for stable 4.9.y.
> >>
> >> This patchset fix race in l2tp sessions, avoid duplicate sessions
> >> and probable "use after free" bugs. Here is the original submission
> >> https://www.mail-archive.com/netdev@vger.kernel.org/msg161040.html
> >>
> >> Cherry-picked and build tested on Linux 4.9.34 for
> >> ARCH=x86/x86_64 + allmodconfig.
> >
> > Thanks for these, should they also go into 4.4 and older kernels?  If
> > so, care to make up patches for them?
> 
> Tried on 4.4 but one or more net-namespace patches are missing in
> between. So I was not sure if I should pull them and other dependent
> patches (if any) into this patchset.

Ok, if you don't think so, that's fine with me, it's just that the
patches said they fixed something that old.  If no one has complained
yet about 4.4 being broken for these issues, don't worry about it :)

thanks,

greg k-h