[XFRM]: Fix potential race vs xfrm_state(only)_find and xfrm_hash_resize.

The _find calls calculate the hash value using the
xfrm_state_hmask, without the xfrm_state_lock. But the
value of this mask can change in the _resize call under
the state_lock, so we risk to fail in finding the desired
entry in hash.

I think, that the hash value is better to calculate
under the state lock.
Signed-off-by: NPavel Emelyanov <xemul@openvz.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/xfrm/xfrm_state.c

@@ -756,7 +756,7 @@ xfrm_state_find(xfrm_address_t *daddr, xfrm_address_t *saddr,
 		struct xfrm_policy *pol, int *err,
 		unsigned short family)
 {
-	unsigned int h = xfrm_dst_hash(daddr, saddr, tmpl->reqid, family);
+	unsigned int h;
 	struct hlist_node *entry;
 	struct xfrm_state *x, *x0;
 	int acquire_in_progress = 0;
@@ -764,6 +764,7 @@ xfrm_state_find(xfrm_address_t *daddr, xfrm_address_t *saddr,
 	struct xfrm_state *best = NULL;
 
 	spin_lock_bh(&xfrm_state_lock);
+	h = xfrm_dst_hash(daddr, saddr, tmpl->reqid, family);
 	hlist_for_each_entry(x, entry, xfrm_state_bydst+h, bydst) {
 		if (x->props.family == family &&
 		    x->props.reqid == tmpl->reqid &&
@@ -865,11 +866,12 @@ struct xfrm_state *
 xfrm_stateonly_find(xfrm_address_t *daddr, xfrm_address_t *saddr,
 		    unsigned short family, u8 mode, u8 proto, u32 reqid)
 {
-	unsigned int h = xfrm_dst_hash(daddr, saddr, reqid, family);
+	unsigned int h;
 	struct xfrm_state *rx = NULL, *x = NULL;
 	struct hlist_node *entry;
 
 	spin_lock(&xfrm_state_lock);
+	h = xfrm_dst_hash(daddr, saddr, reqid, family);
 	hlist_for_each_entry(x, entry, xfrm_state_bydst+h, bydst) {
 		if (x->props.family == family &&
 		    x->props.reqid == reqid &&