From 9e08117c9d4efc1e1bc6fce83dab856d9fd284b6 Mon Sep 17 00:00:00 2001 From: Alan Stern Date: Mon, 7 Oct 2019 12:09:53 -0300 Subject: [PATCH] media: usbvision: Fix races among open, close, and disconnect 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 CC: Signed-off-by: Hans Verkuil Signed-off-by: Mauro Carvalho Chehab --- 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); -- 2.34.1