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Subject: media: usbvision: Fix races among open, close, and disconnect Author: Alan Stern stern@rowland.harvard.edu Date: Mon Oct 7 12:09:53 2019 -0300
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 CC: stable@vger.kernel.org Signed-off-by: Hans Verkuil hverkuil-cisco@xs4all.nl Signed-off-by: Mauro Carvalho Chehab mchehab+samsung@kernel.org
drivers/media/usb/usbvision/usbvision-video.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-)
---
diff --git a/drivers/media/usb/usbvision/usbvision-video.c b/drivers/media/usb/usbvision/usbvision-video.c index 62dec73aec6e..93d36aab824f 100644 --- a/drivers/media/usb/usbvision/usbvision-video.c +++ b/drivers/media/usb/usbvision/usbvision-video.c @@ -314,6 +314,10 @@ static int usbvision_v4l2_open(struct file *file) 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 file *file) 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; @@ -1064,6 +1070,11 @@ static int usbvision_radio_open(struct file *file)
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; @@ -1096,6 +1107,7 @@ out: static int usbvision_radio_close(struct file *file) { struct usb_usbvision *usbvision = video_drvdata(file); + int r;
PDEBUG(DBG_IO, "");
@@ -1109,9 +1121,10 @@ static int usbvision_radio_close(struct file *file) 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); @@ -1543,6 +1556,7 @@ 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, "");
@@ -1559,13 +1573,14 @@ static void usbvision_disconnect(struct usb_interface *intf) 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);