drivers, net: convert masces_rx_sc.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 masces_rx_sc.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>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c
index 733e1c240bf5dae5d56dd43edb5ee5c3feafe7c6..e0aeb51a5daba22906288297a2e0f269890591c3 100644 (file)
--- a/drivers/net/macsec.c
+++ b/drivers/net/macsec.c
@@ -172,7 +172,7 @@ struct macsec_rx_sc {
        bool active;
        struct macsec_rx_sa __rcu *sa[MACSEC_NUM_AN];
        struct pcpu_rx_sc_stats __percpu *stats;
-       atomic_t refcnt;
+       refcount_t refcnt;
        struct rcu_head rcu_head;
 };
 
@@ -331,12 +331,12 @@ static void free_rx_sc_rcu(struct rcu_head *head)
 
 static struct macsec_rx_sc *macsec_rxsc_get(struct macsec_rx_sc *sc)
 {
-       return atomic_inc_not_zero(&sc->refcnt) ? sc : NULL;
+       return refcount_inc_not_zero(&sc->refcnt) ? sc : NULL;
 }
 
 static void macsec_rxsc_put(struct macsec_rx_sc *sc)
 {
-       if (atomic_dec_and_test(&sc->refcnt))
+       if (refcount_dec_and_test(&sc->refcnt))
                call_rcu(&sc->rcu_head, free_rx_sc_rcu);
 }
 
@@ -1411,7 +1411,7 @@ static struct macsec_rx_sc *create_rx_sc(struct net_device *dev, sci_t sci)
 
        rx_sc->sci = sci;
        rx_sc->active = true;
-       atomic_set(&rx_sc->refcnt, 1);
+       refcount_set(&rx_sc->refcnt, 1);
 
        secy = &macsec_priv(dev)->secy;
        rcu_assign_pointer(rx_sc->next, secy->rx_sc);