linux-kernel - [PATCH 27/29] drivers, usb: convert ep_data.count from atomic_t to refcount

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Date:   Mon,  6 Mar 2017 16:21:14 +0200
From:   Elena Reshetova <elena.reshetova@...el.com>
To:     gregkh@...uxfoundation.org
Cc:     linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        netdev@...r.kernel.org, linux1394-devel@...ts.sourceforge.net,
        linux-bcache@...r.kernel.org, linux-raid@...r.kernel.org,
        linux-media@...r.kernel.org, devel@...uxdriverproject.org,
        linux-pci@...r.kernel.org, linux-s390@...r.kernel.org,
        fcoe-devel@...n-fcoe.org, linux-scsi@...r.kernel.org,
        open-iscsi@...glegroups.com, devel@...verdev.osuosl.org,
        target-devel@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-usb@...r.kernel.org, peterz@...radead.org,
        Elena Reshetova <elena.reshetova@...el.com>,
        Hans Liljestrand <ishkamiel@...il.com>,
        Kees Cook <keescook@...omium.org>,
        David Windsor <dwindsor@...il.com>
Subject: [PATCH 27/29] drivers, usb: convert ep_data.count from atomic_t to refcount_t

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
Signed-off-by: Hans Liljestrand <ishkamiel@...il.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
Signed-off-by: David Windsor <dwindsor@...il.com>
---
 drivers/usb/gadget/legacy/inode.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
index 81d76f3..d21a5f8 100644
--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -191,7 +191,7 @@ enum ep_state {
 struct ep_data {
 	struct mutex			lock;
 	enum ep_state			state;
-	atomic_t			count;
+	refcount_t			count;
 	struct dev_data			*dev;
 	/* must hold dev->lock before accessing ep or req */
 	struct usb_ep			*ep;
@@ -206,12 +206,12 @@ struct ep_data {
 
 static inline void get_ep (struct ep_data *data)
 {
-	atomic_inc (&data->count);
+	refcount_inc (&data->count);
 }
 
 static void put_ep (struct ep_data *data)
 {
-	if (likely (!atomic_dec_and_test (&data->count)))
+	if (likely (!refcount_dec_and_test (&data->count)))
 		return;
 	put_dev (data->dev);
 	/* needs no more cleanup */
@@ -1562,7 +1562,7 @@ static int activate_ep_files (struct dev_data *dev)
 		init_waitqueue_head (&data->wait);
 
 		strncpy (data->name, ep->name, sizeof (data->name) - 1);
-		atomic_set (&data->count, 1);
+		refcount_set (&data->count, 1);
 		data->dev = dev;
 		get_dev (dev);
 
-- 
2.7.4