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 <[email protected]> Reviewed-by: David Windsor <[email protected]> Reviewed-by: Hans Liljestrand <[email protected]> Signed-off-by: Elena Reshetova <[email protected]> --- drivers/s390/net/qeth_core.h | 3 ++- drivers/s390/net/qeth_core_main.c | 10 +++++----- 2 files changed, 7 insertions(+), 6 deletions(-) diff --git a/drivers/s390/net/qeth_core.h b/drivers/s390/net/qeth_core.h index 91fcadb..49ba742 100644 --- a/drivers/s390/net/qeth_core.h +++ b/drivers/s390/net/qeth_core.h @@ -20,6 +20,7 @@ #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> @@ -645,7 +646,7 @@ 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 68e118f..86e4c5d 100644 --- a/drivers/s390/net/qeth_core_main.c +++ b/drivers/s390/net/qeth_core_main.c @@ -559,7 +559,7 @@ 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; } @@ -568,14 +568,14 @@ 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); + WARN_ON(refcount_read(&reply->refcnt) == 0); + 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)) + WARN_ON(refcount_read(&reply->refcnt) == 0); + if (refcount_dec_and_test(&reply->refcnt)) kfree(reply); } -- 2.7.4
