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Patch "l2tp: don't use l2tp_tunnel_find() in l2tp_ip and l2tp_ip6" has been added to the 4.13-stable tree

PATCH [email protected] 1 participant 1 message Nov 21, 2017

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This is a note to let you know that I've just added the patch titled

l2tp: don't use l2tp_tunnel_find() in l2tp_ip and l2tp_ip6

to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     l2tp-don-t-use-l2tp_tunnel_find-in-l2tp_ip-and-l2tp_ip6.patch

and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From foo@baz Tue Nov 21 13:07:20 CET 2017

From: Guillaume Nault <[email protected]>
Date: Fri, 3 Nov 2017 16:49:00 +0100
Subject: l2tp: don't use l2tp_tunnel_find() in l2tp_ip and l2tp_ip6

From: Guillaume Nault <[email protected]>

[ Upstream commit 8f7dc9ae4a7aece9fbc3e6637bdfa38b36bcdf09 ]

Using l2tp_tunnel_find() in l2tp_ip_recv() is wrong for two reasons:

* It doesn't take a reference on the returned tunnel, which makes the call racy wrt. concurrent tunnel deletion.

* The lookup is only based on the tunnel identifier, so it can return a tunnel that doesn't match the packet's addresses or protocol.

For example, a packet sent to an L2TPv3 over IPv6 tunnel can be delivered to an L2TPv2 over UDPv4 tunnel. This is worse than a simple
cross-talk: when delivering the packet to an L2TP over UDP tunnel, the corresponding socket is UDP, where ->sk_backlog_rcv() is NULL. Calling sk_receive_skb() will then crash the kernel by trying to execute this callback.

And l2tp_tunnel_find() isn't even needed here. __l2tp_ip_bind_lookup() properly checks the socket binding and connection settings. It was used as a fallback mechanism for finding tunnels that didn't have their data path registered yet. But it's not limited to this case and can be used to replace l2tp_tunnel_find() in the general case.

Fix l2tp_ip6 in the same way.

Fixes 0d76751fad77 ("l2tp: Add L2TPv3 IP encapsulation (no UDP) support")
Fixes a32e0eec7042 ("l2tp: introduce L2TPv3 IP encapsulation support for IPv6")
Signed-off-by Guillaume Nault <[email protected]>
Signed-off-by David S. Miller <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 net/l2tp/l2tp_ip.c  |   24 +++++++++---------------
 net/l2tp/l2tp_ip6.c |   24 +++++++++---------------
 2 files changed, 18 insertions(+), 30 deletions(-)
net/l2tp/l2tp_ip.c +9 -15
@@ -123,6 +123,7 @@ static int l2tp_ip_recv(struct sk_buff *
 	unsigned char *ptr, *optr;
 	struct l2tp_session *session;
 	struct l2tp_tunnel *tunnel = NULL;
+	struct iphdr *iph;
 	int length;
 
 	if (!pskb_may_pull(skb, 4))

@@ -178,24 +179,17 @@ pass_up:
 		goto discard;
 
 	tunnel_id = ntohl(*(__be32 *) &skb->data[4]);
-	tunnel = l2tp_tunnel_find(net, tunnel_id);
-	if (tunnel) {
-		sk = tunnel->sock;
-		sock_hold(sk);
-	} else {
-		struct iphdr *iph = (struct iphdr *) skb_network_header(skb);
-
-		read_lock_bh(&l2tp_ip_lock);
-		sk = __l2tp_ip_bind_lookup(net, iph->daddr, iph->saddr,
-					   inet_iif(skb), tunnel_id);
-		if (!sk) {
-			read_unlock_bh(&l2tp_ip_lock);
-			goto discard;
-		}
+	iph = (struct iphdr *)skb_network_header(skb);
 
-		sock_hold(sk);
+	read_lock_bh(&l2tp_ip_lock);
+	sk = __l2tp_ip_bind_lookup(net, iph->daddr, iph->saddr, inet_iif(skb),
+				   tunnel_id);
+	if (!sk) {
 		read_unlock_bh(&l2tp_ip_lock);
+		goto discard;
 	}
+	sock_hold(sk);
+	read_unlock_bh(&l2tp_ip_lock);
 
 	if (!xfrm4_policy_check(sk, XFRM_POLICY_IN, skb))
 		goto discard_put;
net/l2tp/l2tp_ip6.c +9 -15
@@ -136,6 +136,7 @@ static int l2tp_ip6_recv(struct sk_buff
 	unsigned char *ptr, *optr;
 	struct l2tp_session *session;
 	struct l2tp_tunnel *tunnel = NULL;
+	struct ipv6hdr *iph;
 	int length;
 
 	if (!pskb_may_pull(skb, 4))

@@ -192,24 +193,17 @@ pass_up:
 		goto discard;
 
 	tunnel_id = ntohl(*(__be32 *) &skb->data[4]);
-	tunnel = l2tp_tunnel_find(net, tunnel_id);
-	if (tunnel) {
-		sk = tunnel->sock;
-		sock_hold(sk);
-	} else {
-		struct ipv6hdr *iph = ipv6_hdr(skb);
-
-		read_lock_bh(&l2tp_ip6_lock);
-		sk = __l2tp_ip6_bind_lookup(net, &iph->daddr, &iph->saddr,
-					    inet6_iif(skb), tunnel_id);
-		if (!sk) {
-			read_unlock_bh(&l2tp_ip6_lock);
-			goto discard;
-		}
+	iph = ipv6_hdr(skb);
 
-		sock_hold(sk);
+	read_lock_bh(&l2tp_ip6_lock);
+	sk = __l2tp_ip6_bind_lookup(net, &iph->daddr, &iph->saddr,
+				    inet6_iif(skb), tunnel_id);
+	if (!sk) {
 		read_unlock_bh(&l2tp_ip6_lock);
+		goto discard;
 	}
+	sock_hold(sk);
+	read_unlock_bh(&l2tp_ip6_lock);
 
 	if (!xfrm6_policy_check(sk, XFRM_POLICY_IN, skb))
 		goto discard_put;

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/l2tp-don-t-use-l2tp_tunnel_find-in-l2tp_ip-and-l2tp_ip6.patch