net, xfrm: convert sec_path.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

@@ -1030,7 +1030,7 @@ struct xfrm_offload {
 };
 
 struct sec_path {
-	atomic_t		refcnt;
+	refcount_t		refcnt;
 	int			len;
 	int			olen;
 
@@ -1051,7 +1051,7 @@ static inline struct sec_path *
 secpath_get(struct sec_path *sp)
 {
 	if (sp)
-		atomic_inc(&sp->refcnt);
+		refcount_inc(&sp->refcnt);
 	return sp;
 }
 
@@ -1060,7 +1060,7 @@ void __secpath_destroy(struct sec_path *sp);
 static inline void
 secpath_put(struct sec_path *sp)
 {
-	if (sp && atomic_dec_and_test(&sp->refcnt))
+	if (sp && refcount_dec_and_test(&sp->refcnt))
 		__secpath_destroy(sp);
 }
 

net/xfrm/xfrm_input.c

@@ -116,7 +116,7 @@ struct sec_path *secpath_dup(struct sec_path *src)
 		for (i = 0; i < sp->len; i++)
 			xfrm_state_hold(sp->xvec[i]);
 	}
-	atomic_set(&sp->refcnt, 1);
+	refcount_set(&sp->refcnt, 1);
 	return sp;
 }
 EXPORT_SYMBOL(secpath_dup);
@@ -126,7 +126,7 @@ int secpath_set(struct sk_buff *skb)
 	struct sec_path *sp;
 
 	/* Allocate new secpath or COW existing one. */
-	if (!skb->sp || atomic_read(&skb->sp->refcnt) != 1) {
+	if (!skb->sp || refcount_read(&skb->sp->refcnt) != 1) {
 		sp = secpath_dup(skb->sp);
 		if (!sp)
 			return -ENOMEM;