xfrm: Assign the inner mode output function to the dst entry

As it is, we assign the outer modes output function to the dst entry
when we create the xfrm bundle. This leads to two problems on interfamily
scenarios. We might insert ipv4 packets into ip6_fragment when called
from xfrm6_output. The system crashes if we try to fragment an ipv4
packet with ip6_fragment. This issue was introduced with git commit
ad0081e4 (ipv6: Fragment locally generated tunnel-mode IPSec6 packets
as needed). The second issue is, that we might insert ipv4 packets in
netfilter6 and vice versa on interfamily scenarios.

With this patch we assign the inner mode output function to the dst entry
when we create the xfrm bundle. So xfrm4_output/xfrm6_output from the inner
mode is used and the right fragmentation and netfilter functions are called.
We switch then to outer mode with the output_finish functions.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 1 deletions

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 15792d8b6272..b4d745ea8ee1 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -1406,6 +1406,7 @@ static struct dst_entry *xfrm_bundle_create(struct xfrm_policy *policy,
         struct net *net = xp_net(policy);
         unsigned long now = jiffies;
         struct net_device *dev;
+        struct xfrm_mode *inner_mode;
         struct dst_entry *dst_prev = NULL;
         struct dst_entry *dst0 = NULL;
         int i = 0;
@@ -1436,6 +1437,17 @@ static struct dst_entry *xfrm_bundle_create(struct xfrm_policy *policy,
                         goto put_states;
                 }
 
+                if (xfrm[i]->sel.family == AF_UNSPEC) {
+                        inner_mode = xfrm_ip2inner_mode(xfrm[i],
+                                                        xfrm_af2proto(family));
+                        if (!inner_mode) {
+                                err = -EAFNOSUPPORT;
+                                dst_release(dst);
+                                goto put_states;
+                        }
+                } else
+                        inner_mode = xfrm[i]->inner_mode;
+
                 if (!dst_prev)
                         dst0 = dst1;
                 else {
@@ -1464,7 +1476,7 @@ static struct dst_entry *xfrm_bundle_create(struct xfrm_policy *policy,
                 dst1->lastuse = now;
 
                 dst1->input = dst_discard;
-                dst1->output = xfrm[i]->outer_mode->afinfo->output;
+                dst1->output = inner_mode->afinfo->output;
 
                 dst1->next = dst_prev;
                 dst_prev = dst1;