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Date: Mon, 13 Sep 2021 12:11:54 -0300
From: Igor Matheus Andrade Torrente <igormtorrente@...il.com>
To: Hans Verkuil <hverkuil-cisco@...all.nl>, mchehab@...nel.org,
skhan@...uxfoundation.org, hdanton@...a.com
Cc: linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
kernel test robot <lkp@...el.com>,
syzbot+b2391895514ed9ef4a8e@...kaller.appspotmail.com
Subject: Re: [PATCH v6] media: em28xx: Fix race condition between open and
init function
Hi Hans,
On 9/13/21 6:35 AM, Hans Verkuil wrote:
> 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@...el.com>
>> Reported-and-tested-by: syzbot+b2391895514ed9ef4a8e@...kaller.appspotmail.com
>> Signed-off-by: Igor Matheus Andrade Torrente <igormtorrente@...il.com>
>> ---
>>
>> 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.
If a thread[1] with the `open` syscall pass verification point at
v4l2_open() before the deregistration in the `em28xx_v4l2_fini`.
And If for some reason (e.g page fault) the thread[1] get stuck and
can't get the `dev->lock` before the thread[2](which is in
`em28xx_v4l2_dev_release`).*
The thread[1] will end up accessing freed resources.
Thread[1] |
Open() |
| Time
Thread[1] Thread[2] |
if(vdev==NULL... em28xx_v4l2_fini(em28xx_v4l2_fini) |
▽
Thread[1] Thread[2]
em28xx_v4l2_open(...) b2_video_unregister_device(...)
Thread[1] Thread[2]
PAGE-FAULT v4l2_device_put(&v4l2->v4l2_dev)
Thread[1] Thread[2]
PAGE-FAULT if (refcount_dec_and_test(...))
Thread[1] Thread[2]
PAGE-FAULT em28xx_v4l2_dev_release(...)
Thread[1] Thread[2]
PAGE-FAULT mutex_lock(&dev->lock);
Thread[1] Thread[2]
mutex_lock_interruptible() em28xx_v4l2_dev_unregistr(dev);
Thread[1] Thread[2]
mutex_lock_interruptible() mutex_unlock(&dev->lock)0
Thread[1] Thread[2]
access freed resources kref_put(&dev->ref, em28xx_free_device)
The case above is possible, isn't it?
>
>> 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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