netdev - [PATCH 10/15] drivers, net: convert masces_rx_sc.refcnt from atomic_t to refcount

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Date:   Fri, 20 Oct 2017 10:23:44 +0300
From:   Elena Reshetova <elena.reshetova@...el.com>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-rdma@...r.kernel.org,
        linux-hams@...r.kernel.org, linux-ppp@...r.kernel.org,
        ganeshgr@...lsio.com, nbd@...nwrt.org, john@...ozen.org,
        sean.wang@...iatek.com, matthias.bgg@...il.com,
        yishaih@...lanox.com, saeedm@...lanox.com, matanb@...lanox.com,
        tariqt@...lanox.com, leonro@...lanox.com,
        ajk@...nets.uni-bremen.de, paulus@...ba.org, zbr@...emap.net,
        peterz@...radead.org, keescook@...omium.org,
        Elena Reshetova <elena.reshetova@...el.com>
Subject: [PATCH 10/15] 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@...omium.org>
Reviewed-by: David Windsor <dwindsor@...il.com>
Reviewed-by: Hans Liljestrand <ishkamiel@...il.com>
Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
---
 drivers/net/macsec.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c
index 733e1c2..e0aeb51 100644
--- 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);
-- 
2.7.4