Re: [PATCH v6] media: em28xx: Fix race condition between open and init function

From: Hans Verkuil
Date: Mon Sep 13 2021 - 05:35:35 EST

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On 14/06/2021 21:52, Igor Matheus Andrade Torrente wrote:
> Fixes a race condition - for lack of a more precise term - between
> em28xx_v4l2_open and em28xx_v4l2_init, by managing the em28xx_v4l2
> and v4l2_dev life-time with the v4l2_dev->release() callback.
>
> The race happens when a thread[1] - containing the em28xx_v4l2_init()
> code - calls the v4l2_mc_create_media_graph(), and it return a error,
> if a thread[2] - running v4l2_open() - pass the verification point
> and reaches the em28xx_v4l2_open() before the thread[1] finishes
> the deregistration of v4l2 subsystem, the thread[1] will free all
> resources before the em28xx_v4l2_open() can process their things,
> because the em28xx_v4l2_init() has the dev->lock. And all this lead
> the thread[2] to cause a user-after-free.
>
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Reported-and-tested-by: syzbot+b2391895514ed9ef4a8e@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Igor Matheus Andrade Torrente <igormtorrente@xxxxxxxxx>
> ---
>
> V2: Add v4l2_i2c_new_subdev null check
> Deal with v4l2 subdevs dependencies
>
> V3: Fix link error when compiled as a module
>
> V4: Remove duplicated v4l2_device_disconnect
> in the em28xx_v4l2_fini
>
> V5: Move all the v4l2 resources management
> to the v4l2_dev->release() callback.
>
> V6: Address some Hans comments regarding
> video_unregister_device and struct v4l2_device
> inside the struct v4l2_device.
>
> I'm sending this v6 that way but I'm totally open
> to the Hilt approach, if it is a more desirable
> way to fix this issue.
> ---
> drivers/media/usb/em28xx/em28xx-cards.c | 3 +-
> drivers/media/usb/em28xx/em28xx-video.c | 232 +++++++++++++++---------
> drivers/media/usb/em28xx/em28xx.h | 1 -
> 3 files changed, 151 insertions(+), 85 deletions(-)
>
> diff --git a/drivers/media/usb/em28xx/em28xx-cards.c b/drivers/media/usb/em28xx/em28xx-cards.c
> index ba9292e2a587..6e67cf0a1e04 100644
> --- a/drivers/media/usb/em28xx/em28xx-cards.c
> +++ b/drivers/media/usb/em28xx/em28xx-cards.c
> @@ -4120,7 +4120,6 @@ static void em28xx_usb_disconnect(struct usb_interface *intf)
> struct em28xx *dev;
>
> dev = usb_get_intfdata(intf);
> - usb_set_intfdata(intf, NULL);
>
> if (!dev)
> return;
> @@ -4148,6 +4147,8 @@ static void em28xx_usb_disconnect(struct usb_interface *intf)
> dev->dev_next = NULL;
> }
> kref_put(&dev->ref, em28xx_free_device);
> +
> + usb_set_intfdata(intf, NULL);
> }
>
> static int em28xx_usb_suspend(struct usb_interface *intf,
> diff --git a/drivers/media/usb/em28xx/em28xx-video.c b/drivers/media/usb/em28xx/em28xx-video.c
> index 6b84c3413e83..abf9b325eae4 100644
> --- a/drivers/media/usb/em28xx/em28xx-video.c
> +++ b/drivers/media/usb/em28xx/em28xx-video.c
> @@ -1897,7 +1897,7 @@ static int vidioc_g_chip_info(struct file *file, void *priv,
> strscpy(chip->name, "ac97", sizeof(chip->name));
> else
> strscpy(chip->name,
> - dev->v4l2->v4l2_dev.name, sizeof(chip->name));
> + dev->v4l2->v4l2_dev->name, sizeof(chip->name));
> return 0;
> }
>
> @@ -2113,21 +2113,6 @@ static int radio_s_tuner(struct file *file, void *priv,
> return 0;
> }
>
> -/*
> - * em28xx_free_v4l2() - Free struct em28xx_v4l2
> - *
> - * @ref: struct kref for struct em28xx_v4l2
> - *
> - * Called when all users of struct em28xx_v4l2 are gone
> - */
> -static void em28xx_free_v4l2(struct kref *ref)
> -{
> - struct em28xx_v4l2 *v4l2 = container_of(ref, struct em28xx_v4l2, ref);
> -
> - v4l2->dev->v4l2 = NULL;
> - kfree(v4l2);
> -}
> -
> /*
> * em28xx_v4l2_open()
> * inits the device and starts isoc transfer
> @@ -2153,12 +2138,21 @@ static int em28xx_v4l2_open(struct file *filp)
> return -EINVAL;
> }
>
> + /* To prevent the case when the v4l2_device_put() has already being called,
> + * the ref is now 0, we call a v4l2_device_get, and end up accessing freed
> + * resources. Or straigth accessing a freed v4l2.
> + */
> + if (!v4l2 || !kref_get_unless_zero(&v4l2->v4l2_dev.ref))
> + return -ENODEV;
> +

This should not be needed: once the video devices are unregistered, it is no longer
possible to open the video device. So this can't happen.

> em28xx_videodbg("open dev=%s type=%s users=%d\n",
> video_device_node_name(vdev), v4l2_type_names[fh_type],
> v4l2->users);
>
> - if (mutex_lock_interruptible(&dev->lock))
> + if (mutex_lock_interruptible(&dev->lock)) {
> + v4l2_device_put(&v4l2->v4l2_dev);

So this is also not needed...

> return -ERESTARTSYS;
> + }
>
> ret = v4l2_fh_open(filp);
> if (ret) {
> @@ -2166,6 +2160,7 @@ static int em28xx_v4l2_open(struct file *filp)
> "%s: v4l2_fh_open() returned error %d\n",
> __func__, ret);
> mutex_unlock(&dev->lock);
> + v4l2_device_put(&v4l2->v4l2_dev);

...and neither is this.

> return ret;
> }
>
> @@ -2187,8 +2182,6 @@ static int em28xx_v4l2_open(struct file *filp)
> v4l2_device_call_all(&v4l2->v4l2_dev, 0, tuner, s_radio);
> }
>
> - kref_get(&dev->ref);
> - kref_get(&v4l2->ref);
> v4l2->users++;
>
> mutex_unlock(&dev->lock);
> @@ -2222,36 +2215,30 @@ static int em28xx_v4l2_fini(struct em28xx *dev)
>
> mutex_lock(&dev->lock);
>
> - v4l2_device_disconnect(&v4l2->v4l2_dev);
> -
> em28xx_uninit_usb_xfer(dev, EM28XX_ANALOG_MODE);
>
> - em28xx_v4l2_media_release(dev);
> -
> if (video_is_registered(&v4l2->radio_dev)) {
> - dev_info(&dev->intf->dev, "V4L2 device %s deregistered\n",
> + dev_info(&dev->intf->dev,
> + "V4L2 device %s deregistered\n",
> video_device_node_name(&v4l2->radio_dev));
> - video_unregister_device(&v4l2->radio_dev);
> + vb2_video_unregister_device(&v4l2->radio_dev);
> }
> if (video_is_registered(&v4l2->vbi_dev)) {
> - dev_info(&dev->intf->dev, "V4L2 device %s deregistered\n",
> + dev_info(&dev->intf->dev,
> + "V4L2 device %s deregistered\n",
> video_device_node_name(&v4l2->vbi_dev));
> - video_unregister_device(&v4l2->vbi_dev);
> + vb2_video_unregister_device(&v4l2->vbi_dev);
> }
> if (video_is_registered(&v4l2->vdev)) {
> - dev_info(&dev->intf->dev, "V4L2 device %s deregistered\n",
> + dev_info(&dev->intf->dev,
> + "V4L2 device %s deregistered\n",
> video_device_node_name(&v4l2->vdev));
> - video_unregister_device(&v4l2->vdev);
> + vb2_video_unregister_device(&v4l2->vdev);
> }
>
> - v4l2_ctrl_handler_free(&v4l2->ctrl_handler);
> - v4l2_device_unregister(&v4l2->v4l2_dev);
> -
> - kref_put(&v4l2->ref, em28xx_free_v4l2);
> -
> mutex_unlock(&dev->lock);
>
> - kref_put(&dev->ref, em28xx_free_device);
> + v4l2_device_put(&v4l2->v4l2_dev);
>
> return 0;
> }
> @@ -2323,9 +2310,8 @@ static int em28xx_v4l2_close(struct file *filp)
>
> exit:
> v4l2->users--;
> - kref_put(&v4l2->ref, em28xx_free_v4l2);
> mutex_unlock(&dev->lock);
> - kref_put(&dev->ref, em28xx_free_device);
> + v4l2_device_put(&v4l2->v4l2_dev);

...and neither is this v4l2_device_put.

>
> return 0;
> }
> @@ -2517,6 +2503,28 @@ static void em28xx_tuner_setup(struct em28xx *dev, unsigned short tuner_addr)
> v4l2_device_call_all(v4l2_dev, 0, tuner, s_frequency, &f);
> }
>
> +static void em28xx_v4l2_dev_unregister(struct em28xx *dev)
> +{
> + struct em28xx_v4l2 *v4l2 = dev->v4l2;
> +
> + v4l2_device_unregister(&v4l2->v4l2_dev);
> + em28xx_v4l2_media_release(dev);
> + v4l2_ctrl_handler_free(&v4l2->ctrl_handler);
> +}
> +
> +static void em28xx_v4l2_dev_release(struct v4l2_device *v4l2_dev)
> +{
> + struct em28xx *dev = v4l2_dev->dev->driver_data;
> +
> + mutex_lock(&dev->lock);
> + em28xx_v4l2_dev_unregister(dev);
> + kfree(dev->v4l2);
> + dev->v4l2 = NULL;
> + mutex_unlock(&dev->lock);
> +
> + kref_put(&dev->ref, em28xx_free_device);
> +}
> +
> static int em28xx_v4l2_init(struct em28xx *dev)
> {
> u8 val;
> @@ -2524,6 +2532,7 @@ static int em28xx_v4l2_init(struct em28xx *dev)
> unsigned int maxw;
> struct v4l2_ctrl_handler *hdl;
> struct em28xx_v4l2 *v4l2;
> + struct v4l2_subdev *sd;
>
> if (dev->is_audio_only) {
> /* Shouldn't initialize IR for this interface */
> @@ -2541,12 +2550,13 @@ static int em28xx_v4l2_init(struct em28xx *dev)
>
> v4l2 = kzalloc(sizeof(*v4l2), GFP_KERNEL);
> if (!v4l2) {
> - mutex_unlock(&dev->lock);
> - return -ENOMEM;
> + ret = -ENOMEM;
> + goto err;
> }
> - kref_init(&v4l2->ref);
> +
> v4l2->dev = dev;
> dev->v4l2 = v4l2;
> + v4l2->v4l2_dev.release = em28xx_v4l2_dev_release;
>
> #ifdef CONFIG_MEDIA_CONTROLLER
> v4l2->v4l2_dev.mdev = dev->media_dev;
> @@ -2555,7 +2565,7 @@ static int em28xx_v4l2_init(struct em28xx *dev)
> if (ret < 0) {
> dev_err(&dev->intf->dev,
> "Call to v4l2_device_register() failed!\n");
> - goto err;
> + goto free_v4l2;
> }
>
> hdl = &v4l2->ctrl_handler;
> @@ -2574,25 +2584,53 @@ static int em28xx_v4l2_init(struct em28xx *dev)
>
> /* request some modules */
>
> - if (dev->has_msp34xx)
> - v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
> - &dev->i2c_adap[dev->def_i2c_bus],
> - "msp3400", 0, msp3400_addrs);
> + if (dev->has_msp34xx) {
> + sd = v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
> + &dev->i2c_adap[dev->def_i2c_bus],
> + "msp3400", 0, msp3400_addrs);
> + if (!sd) {
> + dev_err(&dev->intf->dev,
> + "Error while registering 'msp34xx' v4l2 subdevice!\n");
> + ret = -EINVAL;
> + goto unregister_dev;
> + }
> + }
>
> - if (dev->board.decoder == EM28XX_SAA711X)
> - v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
> - &dev->i2c_adap[dev->def_i2c_bus],
> - "saa7115_auto", 0, saa711x_addrs);
> + if (dev->board.decoder == EM28XX_SAA711X) {
> + sd = v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
> + &dev->i2c_adap[dev->def_i2c_bus],
> + "saa7115_auto", 0, saa711x_addrs);
> + if (!sd) {
> + dev_err(&dev->intf->dev,
> + "Error while registering 'EM28XX_SAA711X' v4l2 subdevice!\n");
> + ret = -EINVAL;
> + goto unregister_dev;
> + }
> + }
>
> - if (dev->board.decoder == EM28XX_TVP5150)
> - v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
> - &dev->i2c_adap[dev->def_i2c_bus],
> - "tvp5150", 0, tvp5150_addrs);
> + if (dev->board.decoder == EM28XX_TVP5150) {
> + sd = v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
> + &dev->i2c_adap[dev->def_i2c_bus],
> + "tvp5150", 0, tvp5150_addrs);
> + if (!sd) {
> + dev_err(&dev->intf->dev,
> + "Error while registering 'EM28XX_TVP5150' v4l2 subdevice!\n");
> + ret = -EINVAL;
> + goto unregister_dev;
> + }
> + }
>
> - if (dev->board.adecoder == EM28XX_TVAUDIO)
> - v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
> - &dev->i2c_adap[dev->def_i2c_bus],
> - "tvaudio", dev->board.tvaudio_addr, NULL);
> + if (dev->board.adecoder == EM28XX_TVAUDIO) {
> + sd = v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
> + &dev->i2c_adap[dev->def_i2c_bus],
> + "tvaudio", dev->board.tvaudio_addr, NULL);
> + if (!sd) {
> + dev_err(&dev->intf->dev,
> + "Error while registering 'EM28XX_TVAUDIO' v4l2 subdevice!\n");
> + ret = -EINVAL;
> + goto unregister_dev;
> + }
> + }
>
> /* Initialize tuner and camera */
>
> @@ -2600,33 +2638,63 @@ static int em28xx_v4l2_init(struct em28xx *dev)
> unsigned short tuner_addr = dev->board.tuner_addr;
> int has_demod = (dev->board.tda9887_conf & TDA9887_PRESENT);
>
> - if (dev->board.radio.type)
> - v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
> - &dev->i2c_adap[dev->def_i2c_bus],
> - "tuner", dev->board.radio_addr,
> - NULL);
> -
> - if (has_demod)
> - v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
> - &dev->i2c_adap[dev->def_i2c_bus],
> - "tuner", 0,
> - v4l2_i2c_tuner_addrs(ADDRS_DEMOD));
> + if (dev->board.radio.type) {
> + sd = v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
> + &dev->i2c_adap[dev->def_i2c_bus],
> + "tuner", dev->board.radio_addr,
> + NULL);
> + if (!sd) {
> + dev_err(&dev->intf->dev,
> + "Error while registering '%s' v4l2 subdevice!\n",
> + dev->board.name);
> + ret = -EINVAL;
> + goto unregister_dev;
> + }
> + }
> +
> + if (has_demod) {
> + sd = v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
> + &dev->i2c_adap[dev->def_i2c_bus],
> + "tuner", 0,
> + v4l2_i2c_tuner_addrs(ADDRS_DEMOD));
> + if (!sd) {
> + dev_err(&dev->intf->dev,
> + "Error while registering '%s' v4l2 subdevice!\n",
> + dev->i2c_adap[dev->def_i2c_bus].name);
> + ret = -EINVAL;
> + goto unregister_dev;
> + }
> + }
> +
> if (tuner_addr == 0) {
> enum v4l2_i2c_tuner_type type =
> has_demod ? ADDRS_TV_WITH_DEMOD : ADDRS_TV;
> - struct v4l2_subdev *sd;
>
> sd = v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
> &dev->i2c_adap[dev->def_i2c_bus],
> "tuner", 0,
> v4l2_i2c_tuner_addrs(type));
> -
> - if (sd)
> + if (sd) {
> tuner_addr = v4l2_i2c_subdev_addr(sd);
> + } else {
> + dev_err(&dev->intf->dev,
> + "Error while registering '%s' v4l2 subdevice!\n",
> + dev->i2c_adap[dev->def_i2c_bus].name);
> + ret = -EINVAL;
> + goto unregister_dev;
> + }
> +
> } else {
> - v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
> - &dev->i2c_adap[dev->def_i2c_bus],
> - "tuner", tuner_addr, NULL);
> + sd = v4l2_i2c_new_subdev(&v4l2->v4l2_dev,
> + &dev->i2c_adap[dev->def_i2c_bus],
> + "tuner", tuner_addr, NULL);
> + if (!sd) {
> + dev_err(&dev->intf->dev,
> + "Error while registering '%s' v4l2 subdevice!\n",
> + dev->i2c_adap[dev->def_i2c_bus].name);
> + ret = -EINVAL;
> + goto unregister_dev;
> + }
> }
>
> em28xx_tuner_setup(dev, tuner_addr);
> @@ -2755,7 +2823,6 @@ static int em28xx_v4l2_init(struct em28xx *dev)
> if (ret)
> goto unregister_dev;
>
> - /* allocate and fill video video_device struct */
> em28xx_vdev_init(dev, &v4l2->vdev, &em28xx_video_template, "video");
> mutex_init(&v4l2->vb_queue_lock);
> mutex_init(&v4l2->vb_vbi_queue_lock);
> @@ -2768,7 +2835,6 @@ static int em28xx_v4l2_init(struct em28xx *dev)
> if (dev->tuner_type != TUNER_ABSENT)
> v4l2->vdev.device_caps |= V4L2_CAP_TUNER;
>
> -
> /* disable inapplicable ioctls */
> if (dev->is_webcam) {
> v4l2_disable_ioctl(&v4l2->vdev, VIDIOC_QUERYSTD);
> @@ -2889,26 +2955,26 @@ static int em28xx_v4l2_init(struct em28xx *dev)
> dev_info(&dev->intf->dev,
> "V4L2 device %s deregistered\n",
> video_device_node_name(&v4l2->radio_dev));
> - video_unregister_device(&v4l2->radio_dev);
> + vb2_video_unregister_device(&v4l2->radio_dev);
> }
> if (video_is_registered(&v4l2->vbi_dev)) {
> dev_info(&dev->intf->dev,
> "V4L2 device %s deregistered\n",
> video_device_node_name(&v4l2->vbi_dev));
> - video_unregister_device(&v4l2->vbi_dev);
> + vb2_video_unregister_device(&v4l2->vbi_dev);
> }
> if (video_is_registered(&v4l2->vdev)) {
> dev_info(&dev->intf->dev,
> "V4L2 device %s deregistered\n",
> video_device_node_name(&v4l2->vdev));
> - video_unregister_device(&v4l2->vdev);
> + vb2_video_unregister_device(&v4l2->vdev);
> }
>
> - v4l2_ctrl_handler_free(&v4l2->ctrl_handler);
> - v4l2_device_unregister(&v4l2->v4l2_dev);
> -err:
> + em28xx_v4l2_dev_unregister(dev);
> +free_v4l2:
> + kfree(v4l2);
> dev->v4l2 = NULL;
> - kref_put(&v4l2->ref, em28xx_free_v4l2);
> +err:
> mutex_unlock(&dev->lock);
> return ret;
> }
> diff --git a/drivers/media/usb/em28xx/em28xx.h b/drivers/media/usb/em28xx/em28xx.h
> index ab167cd1f400..666b7eff55f4 100644
> --- a/drivers/media/usb/em28xx/em28xx.h
> +++ b/drivers/media/usb/em28xx/em28xx.h
> @@ -549,7 +549,6 @@ struct em28xx_eeprom {
> #define EM28XX_RESOURCE_VBI 0x02
>
> struct em28xx_v4l2 {
> - struct kref ref;
> struct em28xx *dev;
>
> struct v4l2_device v4l2_dev;
>

With the suggested changes it should be ready (pending testing on my side).

Regards,

Hans

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