[NETFILTER]: Fix bridge netfilter related in xfrm_lookup

The bridge-netfilter code attaches a fake dst_entry with dst->ops == NULL
to purely bridged packets. When these packets are SNATed and a policy
lookup is done, xfrm_lookup crashes because it tries to dereference
dst->ops.

Change xfrm_lookup not to dereference dst->ops before checking for the
DST_NOXFRM flag and set this flag in the fake dst_entry.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 5 insertions, 3 deletions

diff --git a/net/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
index 6bb0c7eb1ef0..e060aad8624d 100644
--- a/net/bridge/br_netfilter.c
+++ b/net/bridge/br_netfilter.c
@@ -90,6 +90,7 @@ static struct rtable __fake_rtable = {
                         .dev                    = &__fake_net_device,
                         .path                   = &__fake_rtable.u.dst,
                         .metrics                = {[RTAX_MTU - 1] = 1500},
+                        .flags                  = DST_NOXFRM,
                 }
         },
         .rt_flags       = 0,
diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 5e6b05ac1260..8206025d8e46 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -782,7 +782,7 @@ int xfrm_lookup(struct dst_entry **dst_p, struct flowi *fl,
         int nx = 0;
         int err;
         u32 genid;
-        u16 family = dst_orig->ops->family;
+        u16 family;
         u8 dir = policy_to_flow_dir(XFRM_POLICY_OUT);
         u32 sk_sid = security_sk_sid(sk, fl, dir);
 restart:
@@ -796,13 +796,14 @@ restart:
                 if ((dst_orig->flags & DST_NOXFRM) || !xfrm_policy_list[XFRM_POLICY_OUT])
                         return 0;
 
-                policy = flow_cache_lookup(fl, sk_sid, family, dir,
-                                           xfrm_policy_lookup);
+                policy = flow_cache_lookup(fl, sk_sid, dst_orig->ops->family,
+                                           dir, xfrm_policy_lookup);
         }
 
         if (!policy)
                 return 0;
 
+        family = dst_orig->ops->family;
         policy->curlft.use_time = (unsigned long)xtime.tv_sec;
 
         switch (policy->action) {