On Wed, Nov 27, 2019 at 11:02:49AM +0100, Nicolas Schier wrote:
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.
Now queued up, thanks.
greg k-h