net, sctp: convert sctp_auth_bytes.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/sctp/auth.h

@@ -31,6 +31,7 @@
 #define __sctp_auth_h__
 
 #include <linux/list.h>
+#include <linux/refcount.h>
 
 struct sctp_endpoint;
 struct sctp_association;
@@ -53,7 +54,7 @@ struct sctp_hmac {
  * over SCTP-AUTH
  */
 struct sctp_auth_bytes {
-	atomic_t refcnt;
+	refcount_t refcnt;
 	__u32 len;
 	__u8  data[];
 };
@@ -76,7 +77,7 @@ static inline void sctp_auth_key_hold(struct sctp_auth_bytes *key)
 	if (!key)
 		return;
 
-	atomic_inc(&key->refcnt);
+	refcount_inc(&key->refcnt);
 }
 
 void sctp_auth_key_put(struct sctp_auth_bytes *key);

net/sctp/auth.c

@@ -63,7 +63,7 @@ void sctp_auth_key_put(struct sctp_auth_bytes *key)
 	if (!key)
 		return;
 
-	if (atomic_dec_and_test(&key->refcnt)) {
+	if (refcount_dec_and_test(&key->refcnt)) {
 		kzfree(key);
 		SCTP_DBG_OBJCNT_DEC(keys);
 	}
@@ -84,7 +84,7 @@ static struct sctp_auth_bytes *sctp_auth_create_key(__u32 key_len, gfp_t gfp)
 		return NULL;
 
 	key->len = key_len;
-	atomic_set(&key->refcnt, 1);
+	refcount_set(&key->refcnt, 1);
 	SCTP_DBG_OBJCNT_INC(keys);
 
 	return key;