net: convert lcs_reply.refcnt from atomic_t to refcount_t

atomic_t variables are currently used to implement reference
counters with the following properties:
 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable lcs_reply.refcnt is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
[jwi: removed the WARN_ONs. Use CONFIG_REFCOUNT_FULL if you care.]
Signed-off-by: Julian Wiedmann <jwi@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 7 deletions

diff --git a/drivers/s390/net/lcs.c b/drivers/s390/net/lcs.c
index 92ae84a..0ee8f33 100644
--- a/drivers/s390/net/lcs.c
+++ b/drivers/s390/net/lcs.c
@@ -756,18 +756,14 @@ lcs_get_lancmd(struct lcs_card *card, int count)
 static void
 lcs_get_reply(struct lcs_reply *reply)
 {
-	WARN_ON(atomic_read(&reply->refcnt) <= 0);
-	atomic_inc(&reply->refcnt);
+	refcount_inc(&reply->refcnt);
 }
 
 static void
 lcs_put_reply(struct lcs_reply *reply)
 {
-        WARN_ON(atomic_read(&reply->refcnt) <= 0);
-        if (atomic_dec_and_test(&reply->refcnt)) {
+	if (refcount_dec_and_test(&reply->refcnt))
 		kfree(reply);
-	}
-
 }
 
 static struct lcs_reply *
@@ -780,7 +776,7 @@ lcs_alloc_reply(struct lcs_cmd *cmd)
 	reply = kzalloc(sizeof(struct lcs_reply), GFP_ATOMIC);
 	if (!reply)
 		return NULL;
-	atomic_set(&reply->refcnt,1);
+	refcount_set(&reply->refcnt, 1);
 	reply->sequence_no = cmd->sequence_no;
 	reply->received = 0;
 	reply->rc = 0;