[Xen-devel] [PATCH 26/29] drivers, usb: convert dev_data.count from atomic_t to refcount_t

[Elena Reshetova <elena.reshetova@xxxxxxxxx>]

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@xxxxxxxxx>
Signed-off-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: David Windsor <dwindsor@xxxxxxxxx>
---
 drivers/usb/gadget/legacy/inode.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/gadget/legacy/inode.c 
b/drivers/usb/gadget/legacy/inode.c
index 79a2d8f..81d76f3 100644
--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -27,6 +27,7 @@
 #include <linux/mmu_context.h>
 #include <linux/aio.h>
 #include <linux/uio.h>
+#include <linux/refcount.h>
 
 #include <linux/device.h>
 #include <linux/moduleparam.h>
@@ -114,7 +115,7 @@ enum ep0_state {
 
 struct dev_data {
        spinlock_t                      lock;
-       atomic_t                        count;
+       refcount_t                      count;
        enum ep0_state                  state;          /* P: lock */
        struct usb_gadgetfs_event       event [N_EVENT];
        unsigned                        ev_next;
@@ -150,12 +151,12 @@ struct dev_data {
 
 static inline void get_dev (struct dev_data *data)
 {
-       atomic_inc (&data->count);
+       refcount_inc (&data->count);
 }
 
 static void put_dev (struct dev_data *data)
 {
-       if (likely (!atomic_dec_and_test (&data->count)))
+       if (likely (!refcount_dec_and_test (&data->count)))
                return;
        /* needs no more cleanup */
        BUG_ON (waitqueue_active (&data->wait));
@@ -170,7 +171,7 @@ static struct dev_data *dev_new (void)
        if (!dev)
                return NULL;
        dev->state = STATE_DEV_DISABLED;
-       atomic_set (&dev->count, 1);
+       refcount_set (&dev->count, 1);
        spin_lock_init (&dev->lock);
        INIT_LIST_HEAD (&dev->epfiles);
        init_waitqueue_head (&dev->wait);
-- 
2.7.4


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