[PATCH net] xfrm: Clear sk_dst_cache when applying per-socket policy.

[Jonathan Basseri]

If an IPv6 socket has a valid dst cache, then xfrm_lookup_route will get
skipped. However, the cache is not invalidated when applying policy to a
socket (i.e. IPV6_XFRM_POLICY). The result is that new policies are
sometimes ignored on those sockets.

This can be demonstrated like so,
1. Create UDPv6 socket.
2. connect() the socket.
3. Apply an outbound XFRM policy to the socket.
4. send() data on the socket.

Packets will continue to be sent in the clear instead of matching an
xfrm or returning a no-match error (EAGAIN). This affects calls to
send() and not sendto().

Note: Creating normal XFRM policies should have a similar effect on
sk_dst_cache entries that match the policy, but that is not fixed in
this patch.

Fixes: 00bc0ef5880d ("ipv6: Skip XFRM lookup if dst_entry in socket cache is 
valid")
Tested: https://android-review.googlesource.com/418659
Signed-off-by: Jonathan Basseri <misterik...@google.com>
---
 net/xfrm/xfrm_state.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 6c0956d10db6..46294cc833f3 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -2028,33 +2028,34 @@ EXPORT_SYMBOL(km_is_alive);
 int xfrm_user_policy(struct sock *sk, int optname, u8 __user *optval, int 
optlen)
 {
        int err;
        u8 *data;
        struct xfrm_mgr *km;
        struct xfrm_policy *pol = NULL;
 
        if (optlen <= 0 || optlen > PAGE_SIZE)
                return -EMSGSIZE;
 
        data = memdup_user(optval, optlen);
        if (IS_ERR(data))
                return PTR_ERR(data);
 
        err = -EINVAL;
        rcu_read_lock();
        list_for_each_entry_rcu(km, &xfrm_km_list, list) {
                pol = km->compile_policy(sk, optname, data,
                                         optlen, &err);
                if (err >= 0)
                        break;
        }
        rcu_read_unlock();
 
        if (err >= 0) {
                xfrm_sk_policy_insert(sk, err, pol);
                xfrm_pol_put(pol);
+               sk_dst_reset(sk);
                err = 0;
        }
 
        kfree(data);
        return err;
 }
-- 
2.14.1.480.gb18f417b89-goog