3.16.82-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Alan Stern stern@rowland.harvard.edu
commit 9e08117c9d4efc1e1bc6fce83dab856d9fd284b6 upstream.
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 stern@rowland.harvard.edu Signed-off-by: Hans Verkuil hverkuil-cisco@xs4all.nl Signed-off-by: Mauro Carvalho Chehab mchehab+samsung@kernel.org [bwh: Backported to 3.16: - Add unlock label in usbvision_v4l2_open() - Adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- --- a/drivers/media/usb/usbvision/usbvision-video.c +++ b/drivers/media/usb/usbvision/usbvision-video.c @@ -348,6 +348,10 @@ 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 { @@ -389,6 +393,7 @@ static int usbvision_v4l2_open(struct fi } }
+unlock: mutex_unlock(&usbvision->v4l2_lock);
PDEBUG(DBG_IO, "success"); @@ -406,6 +411,7 @@ static int usbvision_v4l2_open(struct fi static int usbvision_v4l2_close(struct file *file) { struct usb_usbvision *usbvision = video_drvdata(file); + int r;
PDEBUG(DBG_IO, "close");
@@ -420,9 +426,10 @@ 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; @@ -1136,6 +1143,11 @@ 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; + } if (usbvision->user) { dev_err(&usbvision->rdev->dev, "%s: Someone tried to open an already opened USBVision Radio!\n", @@ -1166,6 +1178,7 @@ static int usbvision_radio_close(struct { struct usb_usbvision *usbvision = video_drvdata(file); int err_code = 0; + int r;
PDEBUG(DBG_IO, "");
@@ -1179,9 +1192,10 @@ 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__); usbvision_release(usbvision); return err_code; @@ -1614,6 +1628,7 @@ 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, "");
@@ -1630,13 +1645,14 @@ 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);