[PATCH net-next 02/15] qeth: convert qeth_reply.refcnt from atomic_t to refcount_t

[Julian Wiedmann]

From: Elena Reshetova <elena.reshet...@intel.com>

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

Suggested-by: Kees Cook <keesc...@chromium.org>
Reviewed-by: David Windsor <dwind...@gmail.com>
Reviewed-by: Hans Liljestrand <ishkam...@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshet...@intel.com>
[jwi: removed the WARN_ONs. Use CONFIG_REFCOUNT_FULL if you care.]
Signed-off-by: Julian Wiedmann <j...@linux.vnet.ibm.com>
---
 drivers/s390/net/qeth_core.h      | 3 ++-
 drivers/s390/net/qeth_core_main.c | 8 +++-----
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/s390/net/qeth_core.h b/drivers/s390/net/qeth_core.h
index badf42acbf95..f5ee62c98011 100644
--- a/drivers/s390/net/qeth_core.h
+++ b/drivers/s390/net/qeth_core.h
@@ -21,6 +21,7 @@
 #include <linux/ethtool.h>
 #include <linux/hashtable.h>
 #include <linux/ip.h>
+#include <linux/refcount.h>
 
 #include <net/ipv6.h>
 #include <net/if_inet6.h>
@@ -632,7 +633,7 @@ struct qeth_reply {
        int rc;
        void *param;
        struct qeth_card *card;
-       atomic_t refcnt;
+       refcount_t refcnt;
 };
 
 struct qeth_card_blkt {
diff --git a/drivers/s390/net/qeth_core_main.c 
b/drivers/s390/net/qeth_core_main.c
index 6c815207f4f5..bc4e57540a9e 100644
--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -564,7 +564,7 @@ static struct qeth_reply *qeth_alloc_reply(struct qeth_card 
*card)
 
        reply = kzalloc(sizeof(struct qeth_reply), GFP_ATOMIC);
        if (reply) {
-               atomic_set(&reply->refcnt, 1);
+               refcount_set(&reply->refcnt, 1);
                atomic_set(&reply->received, 0);
                reply->card = card;
        }
@@ -573,14 +573,12 @@ static struct qeth_reply *qeth_alloc_reply(struct 
qeth_card *card)
 
 static void qeth_get_reply(struct qeth_reply *reply)
 {
-       WARN_ON(atomic_read(&reply->refcnt) <= 0);
-       atomic_inc(&reply->refcnt);
+       refcount_inc(&reply->refcnt);
 }
 
 static void qeth_put_reply(struct qeth_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);
 }
 
-- 
2.13.5