From: Guillaume Nault g.nault@alphalink.fr

commit 8f7dc9ae4a7aece9fbc3e6637bdfa38b36bcdf09 upstream.

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 g.nault@alphalink.fr Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Nicolas Schier n.schier@avm.de --- Please consider queuing this patch for v4.9.y.

net/l2tp/l2tp_ip.c | 24 +++++++++--------------- net/l2tp/l2tp_ip6.c | 24 +++++++++--------------- 2 files changed, 18 insertions(+), 30 deletions(-)

diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c index 03a696d3bcd9..4a88c4eb2301 100644 --- a/net/l2tp/l2tp_ip.c +++ b/net/l2tp/l2tp_ip.c @@ -116,6 +116,7 @@ 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)) @@ -174,24 +175,17 @@ static int l2tp_ip_recv(struct sk_buff *skb) 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; diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c index 8d412b9b0214..423cb095ad37 100644 --- a/net/l2tp/l2tp_ip6.c +++ b/net/l2tp/l2tp_ip6.c @@ -128,6 +128,7 @@ 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)) @@ -187,24 +188,17 @@ static int l2tp_ip6_recv(struct sk_buff *skb) 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;