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Subject[PATCH 4.4 38/65] l2tp: dont use l2tp_tunnel_find() in l2tp_ip and l2tp_ip6
Date
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>
Cc: Nicolas Schier <n.schier@avm.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Giuliano Procida <gprocida@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/l2tp/l2tp_ip.c | 22 ++++++++--------------
net/l2tp/l2tp_ip6.c | 23 ++++++++---------------
2 files changed, 16 insertions(+), 29 deletions(-)

--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -122,6 +122,7 @@ 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))
@@ -180,23 +181,16 @@ 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, 0, 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, 0, 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;
--- a/net/l2tp/l2tp_ip6.c
+++ b/net/l2tp/l2tp_ip6.c
@@ -134,6 +134,7 @@ 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))
@@ -193,24 +194,16 @@ 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,
- 0, 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, 0, 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;

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