net, xfrm: convert xfrm_policy.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: NElena Reshetova <elena.reshetova@intel.com>
Signed-off-by: NHans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: NKees Cook <keescook@chromium.org>
Signed-off-by: NDavid Windsor <dwindsor@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/xfrm.h

@@ -560,7 +560,7 @@ struct xfrm_policy {
 
 	/* This lock only affects elements except for entry. */
 	rwlock_t		lock;
-	atomic_t		refcnt;
+	refcount_t		refcnt;
 	struct timer_list	timer;
 
 	struct flow_cache_object flo;
@@ -816,14 +816,14 @@ static inline void xfrm_audit_state_icvfail(struct xfrm_state *x,
 static inline void xfrm_pol_hold(struct xfrm_policy *policy)
 {
 	if (likely(policy != NULL))
-		atomic_inc(&policy->refcnt);
+		refcount_inc(&policy->refcnt);
 }
 
 void xfrm_policy_destroy(struct xfrm_policy *policy);
 
 static inline void xfrm_pol_put(struct xfrm_policy *policy)
 {
-	if (atomic_dec_and_test(&policy->refcnt))
+	if (refcount_dec_and_test(&policy->refcnt))
 		xfrm_policy_destroy(policy);
 }
 

net/key/af_key.c

@@ -2177,7 +2177,7 @@ static int pfkey_xfrm_policy2msg(struct sk_buff *skb, const struct xfrm_policy *
 	}
 
 	hdr->sadb_msg_len = size / sizeof(uint64_t);
-	hdr->sadb_msg_reserved = atomic_read(&xp->refcnt);
+	hdr->sadb_msg_reserved = refcount_read(&xp->refcnt);
 
 	return 0;
 }

net/xfrm/xfrm_policy.c

@@ -62,7 +62,7 @@ static struct xfrm_policy *__xfrm_policy_unlink(struct xfrm_policy *pol,
 
 static inline bool xfrm_pol_hold_rcu(struct xfrm_policy *policy)
 {
-	return atomic_inc_not_zero(&policy->refcnt);
+	return refcount_inc_not_zero(&policy->refcnt);
 }
 
 static inline bool
@@ -292,7 +292,7 @@ struct xfrm_policy *xfrm_policy_alloc(struct net *net, gfp_t gfp)
 		INIT_HLIST_NODE(&policy->bydst);
 		INIT_HLIST_NODE(&policy->byidx);
 		rwlock_init(&policy->lock);
-		atomic_set(&policy->refcnt, 1);
+		refcount_set(&policy->refcnt, 1);
 		skb_queue_head_init(&policy->polq.hold_queue);
 		setup_timer(&policy->timer, xfrm_policy_timer,
 				(unsigned long)policy);