xfrm: fix "disable_policy" flag use when arriving from different devices

In IPv4 setting the "disable_policy" flag on a device means no policy
should be enforced for traffic originating from the device. This was
implemented by seting the DST_NOPOLICY flag in the dst based on the
originating device.

However, dsts are cached in nexthops regardless of the originating
devices, in which case, the DST_NOPOLICY flag value may be incorrect.

Consider the following setup:

                     +------------------------------+
                     | ROUTER                       |
  +-------------+    | +-----------------+          |
  | ipsec src   |----|-|ipsec0           |          |
  +-------------+    | |disable_policy=0 |   +----+ |
                     | +-----------------+   |eth1|-|-----
  +-------------+    | +-----------------+   +----+ |
  | noipsec src |----|-|eth0             |          |
  +-------------+    | |disable_policy=1 |          |
                     | +-----------------+          |
                     +------------------------------+

Where ROUTER has a default route towards eth1.

dst entries for traffic arriving from eth0 would have DST_NOPOLICY
and would be cached and therefore can be reused by traffic originating
from ipsec0, skipping policy check.

Fix by setting a IPSKB_NOPOLICY flag in IPCB and observing it instead
of the DST in IN/FWD IPv4 policy checks.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

1 files changed, 13 insertions, 1 deletions

diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 6fb899ff5afc..d2efddce65d4 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -1093,6 +1093,18 @@ static inline bool __xfrm_check_nopolicy(struct net *net, struct sk_buff *skb,
 	return false;
 }
 
+static inline bool __xfrm_check_dev_nopolicy(struct sk_buff *skb,
+					     int dir, unsigned short family)
+{
+	if (dir != XFRM_POLICY_OUT && family == AF_INET) {
+		/* same dst may be used for traffic originating from
+		 * devices with different policy settings.
+		 */
+		return IPCB(skb)->flags & IPSKB_NOPOLICY;
+	}
+	return skb_dst(skb) && (skb_dst(skb)->flags & DST_NOPOLICY);
+}
+
 static inline int __xfrm_policy_check2(struct sock *sk, int dir,
 				       struct sk_buff *skb,
 				       unsigned int family, int reverse)
@@ -1104,7 +1116,7 @@ static inline int __xfrm_policy_check2(struct sock *sk, int dir,
 		return __xfrm_policy_check(sk, ndir, skb, family);
 
 	return __xfrm_check_nopolicy(net, skb, dir) ||
-	       (skb_dst(skb) && (skb_dst(skb)->flags & DST_NOPOLICY)) ||
+	       __xfrm_check_dev_nopolicy(skb, dir, family) ||
 	       __xfrm_policy_check(sk, ndir, skb, family);
 }