l2tp: don't use l2tp_tunnel_find() in l2tp_ip and l2tp_ip6 (8f7dc9ae) · Commits · 戴 / test

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: ("l2tp: Add L2TPv3 IP encapsulation (no UDP) support") Fixes: ("l2tp: introduce L2TPv3 IP encapsulation support for IPv6") Signed-off-by:

Guillaume Nault <g.nault@alphalink.fr> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/l2tp/l2tp_ip.c

+9 −15

Original line number	Diff line number	Diff line
		@@ -123,6 +123,7 @@ static int l2tp_ip_recv(struct sk_buff *skb)
		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);
		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);
		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

Original line number	Diff line number	Diff line
		@@ -136,6 +136,7 @@ static int l2tp_ip6_recv(struct sk_buff *skb)
		unsigned char ptr, optr;
		struct l2tp_session *session;
		struct l2tp_tunnel *tunnel = NULL;
		struct ipv6hdr *iph;
		int length;

		if (!pskb_may_pull(skb, 4))
		@@ -192,12 +193,7 @@ 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);
		iph = ipv6_hdr(skb);

		read_lock_bh(&l2tp_ip6_lock);
		sk = __l2tp_ip6_bind_lookup(net, &iph->daddr, &iph->saddr,
		@@ -206,10 +202,8 @@ pass_up:
		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;

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