* [PATCH 1/1] l2tp: don't use l2tp_tunnel_find() in l2tp_ip and l2tp_ip6
2019-11-27 10:02 [PATCH 0/1] Missing l2tp patch in v4.9.y series Nicolas Schier
@ 2019-11-27 10:02 ` Nicolas Schier
2019-11-27 10:28 ` Greg KH
0 siblings, 1 reply; 3+ messages in thread
From: Nicolas Schier @ 2019-11-27 10:02 UTC (permalink / raw)
To: stable; +Cc: Nicolas Schier, Guillaume Nault, David S . Miller
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;
--
2.24.0
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