net, xfrm: convert xfrm_state.refcnt from atomic_t to refcount_t

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/xfrm.h

@@ -13,6 +13,7 @@
 #include <linux/mutex.h>
 #include <linux/audit.h>
 #include <linux/slab.h>
+#include <linux/refcount.h>
 
 #include <net/sock.h>
 #include <net/dst.h>
@@ -137,7 +138,7 @@ struct xfrm_state {
 	struct hlist_node	bysrc;
 	struct hlist_node	byspi;
 
-	atomic_t		refcnt;
+	refcount_t		refcnt;
 	spinlock_t		lock;
 
 	struct xfrm_id		id;
@@ -837,18 +838,18 @@ void __xfrm_state_destroy(struct xfrm_state *);
 
 static inline void __xfrm_state_put(struct xfrm_state *x)
 {
-	atomic_dec(&x->refcnt);
+	refcount_dec(&x->refcnt);
 }
 
 static inline void xfrm_state_put(struct xfrm_state *x)
 {
-	if (atomic_dec_and_test(&x->refcnt))
+	if (refcount_dec_and_test(&x->refcnt))
 		__xfrm_state_destroy(x);
 }
 
 static inline void xfrm_state_hold(struct xfrm_state *x)
 {
-	atomic_inc(&x->refcnt);
+	refcount_inc(&x->refcnt);
 }
 
 static inline bool addr_match(const void *token1, const void *token2,

net/xfrm/xfrm_state.c

@@ -48,7 +48,7 @@ static HLIST_HEAD(xfrm_state_gc_list);
 
 static inline bool xfrm_state_hold_rcu(struct xfrm_state __rcu *x)
 {
-	return atomic_inc_not_zero(&x->refcnt);
+	return refcount_inc_not_zero(&x->refcnt);
 }
 
 static inline unsigned int xfrm_dst_hash(struct net *net,
@@ -558,7 +558,7 @@ struct xfrm_state *xfrm_state_alloc(struct net *net)
 
 	if (x) {
 		write_pnet(&x->xs_net, net);
-		atomic_set(&x->refcnt, 1);
+		refcount_set(&x->refcnt, 1);
 		atomic_set(&x->tunnel_users, 0);
 		INIT_LIST_HEAD(&x->km.all);
 		INIT_HLIST_NODE(&x->bydst);