[PATCH 12/29] drivers, media: convert s2255_dev.num_channels from atomic_t to refcount_t

Elena Reshetova
2017-03-06T14:20:59Z

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@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
drivers/media/usb/s2255/s2255drv.c | 21 +++++++++++----------
1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/drivers/media/usb/s2255/s2255drv.c b/drivers/media/usb/s2255/s2255drv.c
index a9d4484..2b4b009 100644
--- a/drivers/media/usb/s2255/s2255drv.c
+++ b/drivers/media/usb/s2255/s2255drv.c
@@ -36,6 +36,7 @@
#include <linux/firmware.h>
#include <linux/kernel.h>
#include <linux/mutex.h>
+#include <linux/refcount.h>
#include <linux/slab.h>
#include <linux/videodev2.h>
#include <linux/mm.h>
@@ -256,7 +257,7 @@ struct s2255_vc {
struct s2255_dev {
struct s2255_vc vc[MAX_CHANNELS];
struct v4l2_device v4l2_dev;
- atomic_t num_channels;
+ refcount_t num_channels;
int frames;
struct mutex lock; /* channels[].vdev.lock */
struct mutex cmdlock; /* protects cmdbuf */
@@ -1581,11 +1582,11 @@ static void s2255_video_device_release(struct video_device *vdev)
container_of(vdev, struct s2255_vc, vdev);

dprintk(dev, 4, "%s, chnls: %d\n", __func__,
- atomic_read(&dev->num_channels));
+ refcount_read(&dev->num_channels));

v4l2_ctrl_handler_free(&vc->hdl);

- if (atomic_dec_and_test(&dev->num_channels))
+ if (refcount_dec_and_test(&dev->num_channels))
s2255_destroy(dev);
return;
}
@@ -1688,7 +1689,7 @@ static int s2255_probe_v4l(struct s2255_dev *dev)
"failed to register video device!\n");
break;
}
- atomic_inc(&dev->num_channels);
+ refcount_set(&dev->num_channels, 1);
v4l2_info(&dev->v4l2_dev, "V4L2 device registered as %s\n",
video_device_node_name(&vc->vdev));

@@ -1696,11 +1697,11 @@ static int s2255_probe_v4l(struct s2255_dev *dev)
pr_info("Sensoray 2255 V4L driver Revision: %s\n",
S2255_VERSION);
/* if no channels registered, return error and probe will fail*/
- if (atomic_read(&dev->num_channels) == 0) {
+ if (refcount_read(&dev->num_channels) == 0) {
v4l2_device_unregister(&dev->v4l2_dev);
return ret;
}
- if (atomic_read(&dev->num_channels) != MAX_CHANNELS)
+ if (refcount_read(&dev->num_channels) != MAX_CHANNELS)
pr_warn("s2255: Not all channels available.\n");
return 0;
}
@@ -2248,7 +2249,7 @@ static int s2255_probe(struct usb_interface *interface,
goto errorFWDATA1;
}

- atomic_set(&dev->num_channels, 0);
+ refcount_set(&dev->num_channels, 0);
dev->pid = id->idProduct;
dev->fw_data = kzalloc(sizeof(struct s2255_fw), GFP_KERNEL);
if (!dev->fw_data)
@@ -2368,12 +2369,12 @@ static void s2255_disconnect(struct usb_interface *interface)
{
struct s2255_dev *dev = to_s2255_dev(usb_get_intfdata(interface));
int i;
- int channels = atomic_read(&dev->num_channels);
+ int channels = refcount_read(&dev->num_channels);
mutex_lock(&dev->lock);
v4l2_device_disconnect(&dev->v4l2_dev);
mutex_unlock(&dev->lock);
/*see comments in the uvc_driver.c usb disconnect function */
- atomic_inc(&dev->num_channels);
+ refcount_inc(&dev->num_channels);
/* unregister each video device. */
for (i = 0; i < channels; i++)
video_unregister_device(&dev->vc[i].vdev);
@@ -2386,7 +2387,7 @@ static void s2255_disconnect(struct usb_interface *interface)
dev->vc[i].vidstatus_ready = 1;
wake_up(&dev->vc[i].wait_vidstatus);
}
- if (atomic_dec_and_test(&dev->num_channels))
+ if (refcount_dec_and_test(&dev->num_channels))
s2255_destroy(dev);
dev_info(&interface->dev, "%s\n", __func__);
}
--
2.7.4