xfrm: check bundle policy existance before dereferencing it

Fix the bundle validation code to not assume having a valid policy.
When we have multiple transformations for a xfrm policy, the bundle
instance will be a chain of bundles with only the first one having
the policy reference. When policy_genid is bumped it will expire the
first bundle in the chain which is equivalent of expiring the whole
chain.

Reported-bisected-and-tested-by: Justin P. Mattock <justinmattock@gmail.com>
Signed-off-by: Timo Teräs <timo.teras@iki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 4bf27d901333..af1c173be4ad 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -2300,7 +2300,8 @@ int xfrm_bundle_ok(struct xfrm_policy *pol, struct xfrm_dst *first,
                         return 0;
                 if (xdst->xfrm_genid != dst->xfrm->genid)
                         return 0;
-                if (xdst->policy_genid != atomic_read(&xdst->pols[0]->genid))
+                if (xdst->num_pols > 0 &&
+                    xdst->policy_genid != atomic_read(&xdst->pols[0]->genid))
                         return 0;
 
                 if (strict && fl &&