Visual inspection of the usbvision driver shows that it suffers from
three races between its open, close, and disconnect handlers. In
particular, the driver is careful to update its usbvision->user and
usbvision->remove_pending flags while holding the private mutex, but:
usbvision_v4l2_close() and usbvision_radio_close() don't hold
the mutex while they check the value of
usbvision->remove_pending;
usbvision_disconnect() doesn't hold the mutex while checking
the value of usbvision->user; and
also, usbvision_v4l2_open() and usbvision_radio_open() don't
check whether the device has been unplugged before allowing
the user to open the device files.
Each of these can potentially lead to usbvision_release() being called
twice and use-after-free errors.
This patch fixes the races by reading the flags while the mutex is
still held and checking for pending removes before allowing an open to
succeed.
Signed-off-by: Alan Stern <st...@rowland.harvard.edu>
CC: <sta...@vger.kernel.org>
---
[as1920]
drivers/media/usb/usbvision/usbvision-video.c | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)
Index: usb-devel/drivers/media/usb/usbvision/usbvision-video.c
===================================================================
--- usb-devel.orig/drivers/media/usb/usbvision/usbvision-video.c
+++ usb-devel/drivers/media/usb/usbvision/usbvision-video.c
@@ -314,6 +314,10 @@ static int usbvision_v4l2_open(struct fi
if (mutex_lock_interruptible(&usbvision->v4l2_lock))
return -ERESTARTSYS;
+ if (usbvision->remove_pending) {
+ err_code = -ENODEV;
+ goto unlock;
+ }
if (usbvision->user) {
err_code = -EBUSY;
} else {
@@ -377,6 +381,7 @@ unlock:
static int usbvision_v4l2_close(struct file *file)
{
struct usb_usbvision *usbvision = video_drvdata(file);
+ int r;
PDEBUG(DBG_IO, "close");
@@ -391,9 +396,10 @@ static int usbvision_v4l2_close(struct f
usbvision_scratch_free(usbvision);
usbvision->user--;
+ r = usbvision->remove_pending;
mutex_unlock(&usbvision->v4l2_lock);
- if (usbvision->remove_pending) {
+ if (r) {
printk(KERN_INFO "%s: Final disconnect\n", __func__);
usbvision_release(usbvision);
return 0;
@@ -1076,6 +1082,11 @@ static int usbvision_radio_open(struct f
if (mutex_lock_interruptible(&usbvision->v4l2_lock))
return -ERESTARTSYS;
+
+ if (usbvision->remove_pending) {
+ err_code = -ENODEV;
+ goto out;
+ }
err_code = v4l2_fh_open(file);
if (err_code)
goto out;
@@ -1108,6 +1119,7 @@ out:
static int usbvision_radio_close(struct file *file)
{
struct usb_usbvision *usbvision = video_drvdata(file);
+ int r;
PDEBUG(DBG_IO, "");
@@ -1121,9 +1133,10 @@ static int usbvision_radio_close(struct
usbvision_audio_off(usbvision);
usbvision->radio = 0;
usbvision->user--;
+ r = usbvision->remove_pending;
mutex_unlock(&usbvision->v4l2_lock);
- if (usbvision->remove_pending) {
+ if (r) {
printk(KERN_INFO "%s: Final disconnect\n", __func__);
v4l2_fh_release(file);
usbvision_release(usbvision);
@@ -1555,6 +1568,7 @@ err_usb:
static void usbvision_disconnect(struct usb_interface *intf)
{
struct usb_usbvision *usbvision = to_usbvision(usb_get_intfdata(intf));
+ int u;
PDEBUG(DBG_PROBE, "");
@@ -1571,13 +1585,14 @@ static void usbvision_disconnect(struct
v4l2_device_disconnect(&usbvision->v4l2_dev);
usbvision_i2c_unregister(usbvision);
usbvision->remove_pending = 1; /* Now all ISO data will be ignored */
+ u = usbvision->user;
usb_put_dev(usbvision->dev);
usbvision->dev = NULL; /* USB device is no more */
mutex_unlock(&usbvision->v4l2_lock);
- if (usbvision->user) {
+ if (u) {
printk(KERN_INFO "%s: In use, disconnect pending\n",
__func__);
wake_up_interruptible(&usbvision->wait_frame);
