Re: [PATCH v5 3/3] media: vimc: use-after-free fix - release vimc in the v4l_device release

[Dafna Hirschfeld <dafna.hirschfeld@collabora.com>]

On 24.01.20 12:31, Hans Verkuil wrote:
> On 1/23/20 12:36 PM, Dafna Hirschfeld wrote:
>> Hi
>>
>> On 22.01.20 17:39, Helen Koike wrote:
>>> Hi Dafna,
>>>
>>> Thanks for the patch.
>>>
>>> On 1/22/20 2:01 PM, Dafna Hirschfeld wrote:
>>>> A use-after-free bug occures when unbinding the device while it streams.
>>>> The 'struct vimc_ent_device' allocated for the 'Sensor A' is freed
>>>> when calling the sensor's 'rm' callback but the freed pointer is
>>>> later accessed in the function 'vimc_streamer_pipeline_terminate'.
>>>> To fix this bug, move the release callback of the vimc entities
>>>> and vimc_device to the release callback of v4l2_device.
>>>> The .rm callback of vimc_ent_config is replaced by two callbacks:
>>>>
>>>> .unregister - this is called upon removing the device and
>>>> it unregisters the entity. This is an optional callback since
>>>> subdevices don't need to implement it because they are already
>>>> unregistered in v4l2_device_unregister.
>>>>
>>>> .release - this is called from the release callback of v4l2_device
>>>> and it frees the entity.
>>>>
>>>> This ensures that the entities will be released when the last fh
>>>> of any of the devices is closed.
>>>>
>>>> The commands that cause the crash and the KASAN report:
>>>>
>>>> media-ctl -d platform:vimc -V '"Sensor A":0[fmt:SBGGR8_1X8/640x480]'
>>>> media-ctl -d platform:vimc -V '"Debayer A":0[fmt:SBGGR8_1X8/640x480]'
>>>> v4l2-ctl -z platform:vimc -d "RGB/YUV Capture" -v width=1920,height=1440
>>>> v4l2-ctl -z platform:vimc -d "Raw Capture 0" -v pixelformat=BA81
>>>> v4l2-ctl --stream-mmap --stream-count=1000 -d /dev/video2 &
>>>> sleep 1
>>>> echo -n vimc.0 >/sys/bus/platform/drivers/vimc/unbind
>>>>
>>>> [  188.417934] BUG: KASAN: use-after-free in vimc_streamer_pipeline_terminate+0x75/0x140 [vimc]
>>>> [  188.420182] Read of size 8 at addr ffff8881e9c26008 by task bash/185
>>>> [  188.421800]
>>>> [  188.422223] CPU: 0 PID: 185 Comm: bash Not tainted 5.5.0-rc1+ #1
>>>> [  188.423681] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
>>>> [  188.425938] Call Trace:
>>>> [  188.426610]  dump_stack+0x75/0xa0
>>>> [  188.427519]  ? vimc_streamer_pipeline_terminate+0x75/0x140 [vimc]
>>>> [  188.429057]  print_address_description.constprop.6+0x16/0x220
>>>> [  188.430462]  ? vimc_streamer_pipeline_terminate+0x75/0x140 [vimc]
>>>> [  188.431979]  ? vimc_streamer_pipeline_terminate+0x75/0x140 [vimc]
>>>> [  188.433455]  __kasan_report.cold.9+0x1a/0x40
>>>> [  188.434518]  ? vimc_streamer_pipeline_terminate+0x75/0x140 [vimc]
>>>> [  188.436010]  kasan_report+0xe/0x20
>>>> [  188.436859]  vimc_streamer_pipeline_terminate+0x75/0x140 [vimc]
>>>> [  188.438339]  vimc_streamer_s_stream+0x8b/0x3c0 [vimc]
>>>> [  188.439576]  vimc_cap_stop_streaming+0x22/0x40 [vimc]
>>>> [  188.440863]  __vb2_queue_cancel+0x65/0x560 [videobuf2_common]
>>>> [  188.442391]  vb2_core_queue_release+0x19/0x50 [videobuf2_common]
>>>> [  188.443974]  vimc_cap_rm+0x10/0x20 [vimc]
>>>> [  188.444986]  vimc_rm_subdevs+0x9e/0xe0 [vimc]
>>>> [  188.446179]  vimc_remove+0x19/0x70 [vimc]
>>>> [  188.447301]  platform_drv_remove+0x2f/0x50
>>>> [  188.448468]  device_release_driver_internal+0x133/0x260
>>>> [  188.449814]  unbind_store+0x121/0x150
>>>> [  188.450726]  kernfs_fop_write+0x142/0x230
>>>> [  188.451724]  ? sysfs_kf_bin_read+0x100/0x100
>>>> [  188.452826]  vfs_write+0xdc/0x230
>>>> [  188.453760]  ksys_write+0xaf/0x140
>>>> [  188.454702]  ? __ia32_sys_read+0x40/0x40
>>>> [  188.455773]  ? __do_page_fault+0x473/0x620
>>>> [  188.456780]  do_syscall_64+0x5e/0x1a0
>>>> [  188.457711]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>>> [  188.459079] RIP: 0033:0x7f80f1f13504
>>>> [  188.459969] Code: 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b3 0f 1f 80 00 00 00 00 48 8d 05 f9 61 0d 00 8b 00 85 c0 75 13 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 41 54 49 89
>>>> d4 55 48 89 f5 53
>>>> [  188.464445] RSP: 002b:00007ffd7e843b58 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
>>>> [  188.466276] RAX: ffffffffffffffda RBX: 0000000000000006 RCX: 00007f80f1f13504
>>>> [  188.467999] RDX: 0000000000000006 RSI: 000055ef2eb21b10 RDI: 0000000000000001
>>>> [  188.469708] RBP: 000055ef2eb21b10 R08: 00007f80f1fe68c0 R09: 00007f80f1e26740
>>>> [  188.471407] R10: 000055ef2eade010 R11: 0000000000000246 R12: 00007f80f1fe5760
>>>> [  188.473381] R13: 0000000000000006 R14: 00007f80f1fe0760 R15: 0000000000000006
>>>> [  188.475107]
>>>> [  188.475500] Allocated by task 473:
>>>> [  188.476351]  save_stack+0x19/0x80
>>>> [  188.477201]  __kasan_kmalloc.constprop.6+0xc1/0xd0
>>>> [  188.478507]  vimc_sen_add+0x36/0x309 [vimc]
>>>> [  188.479649]  vimc_probe+0x1e2/0x530 [vimc]
>>>> [  188.480776]  platform_drv_probe+0x46/0xa0
>>>> [  188.481829]  really_probe+0x16c/0x520
>>>> [  188.482732]  driver_probe_device+0x114/0x170
>>>> [  188.483783]  device_driver_attach+0x85/0x90
>>>> [  188.484800]  __driver_attach+0xa8/0x190
>>>> [  188.485734]  bus_for_each_dev+0xe4/0x140
>>>> [  188.486702]  bus_add_driver+0x223/0x2d0
>>>> [  188.487715]  driver_register+0xca/0x140
>>>> [  188.488767]  0xffffffffc037003d
>>>> [  188.489635]  do_one_initcall+0x86/0x28f
>>>> [  188.490702]  do_init_module+0xf8/0x340
>>>> [  188.491773]  load_module+0x3766/0x3a10
>>>> [  188.492811]  __do_sys_finit_module+0x11a/0x1b0
>>>> [  188.494059]  do_syscall_64+0x5e/0x1a0
>>>> [  188.495079]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>>> [  188.496481]
>>>> [  188.496893] Freed by task 185:
>>>> [  188.497670]  save_stack+0x19/0x80
>>>> [  188.498493]  __kasan_slab_free+0x125/0x170
>>>> [  188.499486]  kfree+0x8c/0x230
>>>> [  188.500254]  v4l2_subdev_release+0x64/0x70 [videodev]
>>>> [  188.501498]  v4l2_device_release_subdev_node+0x1c/0x30 [videodev]
>>>> [  188.502976]  device_release+0x3c/0xd0
>>>> [  188.503867]  kobject_put+0xf4/0x240
>>>> [  188.507802]  vimc_rm_subdevs+0x9e/0xe0 [vimc]
>>>> [  188.508846]  vimc_remove+0x19/0x70 [vimc]
>>>> [  188.509792]  platform_drv_remove+0x2f/0x50
>>>> [  188.510752]  device_release_driver_internal+0x133/0x260
>>>> [  188.512006]  unbind_store+0x121/0x150
>>>> [  188.512899]  kernfs_fop_write+0x142/0x230
>>>> [  188.513874]  vfs_write+0xdc/0x230
>>>> [  188.514698]  ksys_write+0xaf/0x140
>>>> [  188.515523]  do_syscall_64+0x5e/0x1a0
>>>> [  188.516543]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>>> [  188.517710]
>>>> [  188.518034] The buggy address belongs to the object at ffff8881e9c26000
>>>> [  188.518034]  which belongs to the cache kmalloc-4k of size 4096
>>>> [  188.520528] The buggy address is located 8 bytes inside of
>>>> [  188.520528]  4096-byte region [ffff8881e9c26000, ffff8881e9c27000)
>>>> [  188.523015] The buggy address belongs to the page:
>>>> [  188.524357] page:ffffea0007a70800 refcount:1 mapcount:0 mapping:ffff8881f6402140 index:0x0 compound_mapcount: 0
>>>> [  188.527058] raw: 0200000000010200 dead000000000100 dead000000000122 ffff8881f6402140
>>>> [  188.528983] raw: 0000000000000000 0000000000040004 00000001ffffffff 0000000000000000
>>>> [  188.530883] page dumped because: kasan: bad access detected
>>>> [  188.532336]
>>>> [  188.532720] Memory state around the buggy address:
>>>> [  188.533871]  ffff8881e9c25f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>>> [  188.535631]  ffff8881e9c25f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>>> [  188.537370] >ffff8881e9c26000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>> [  188.538996]                       ^
>>>> [  188.539812]  ffff8881e9c26080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>> [  188.541549]  ffff8881e9c26100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>>
>>>> Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
>>>> ---
>>>>    drivers/media/platform/vimc/vimc-capture.c | 12 ++---
>>>>    drivers/media/platform/vimc/vimc-common.c  |  2 -
>>>>    drivers/media/platform/vimc/vimc-common.h  | 25 ++++-----
>>>>    drivers/media/platform/vimc/vimc-core.c    | 61 +++++++++++++++-------
>>>>    drivers/media/platform/vimc/vimc-debayer.c | 19 ++-----
>>>>    drivers/media/platform/vimc/vimc-scaler.c  | 19 ++-----
>>>>    drivers/media/platform/vimc/vimc-sensor.c  | 18 ++-----
>>>>    7 files changed, 71 insertions(+), 85 deletions(-)
>>>>
>>>> diff --git a/drivers/media/platform/vimc/vimc-capture.c b/drivers/media/platform/vimc/vimc-capture.c
>>>> index 9a78bb7826a8..c5a645f98c66 100644
>>>> --- a/drivers/media/platform/vimc/vimc-capture.c
>>>> +++ b/drivers/media/platform/vimc/vimc-capture.c
>>>> @@ -325,20 +325,20 @@ static const struct media_entity_operations vimc_cap_mops = {
>>>>        .link_validate        = vimc_vdev_link_validate,
>>>>    };
>>>>    -static void vimc_cap_release(struct video_device *vdev)
>>>> +void vimc_cap_release(struct vimc_ent_device *ved)
>>>>    {
>>>>        struct vimc_cap_device *vcap =
>>>> -        container_of(vdev, struct vimc_cap_device, vdev);
>>>> +        container_of(ved, struct vimc_cap_device, ved);
>>>>          media_entity_cleanup(vcap->ved.ent);
>>>>        kfree(vcap);
>>>>    }
>>>>    -void vimc_cap_rm(struct vimc_device *vimc, struct vimc_ent_device *ved)
>>>> +void vimc_cap_unregister(struct vimc_ent_device *ved)
>>>>    {
>>>> -    struct vimc_cap_device *vcap;
>>>> +    struct vimc_cap_device *vcap =
>>>> +        container_of(ved, struct vimc_cap_device, ved);
>>>>    -    vcap = container_of(ved, struct vimc_cap_device, ved);
>>>>        vb2_queue_release(&vcap->queue);
>>>>        video_unregister_device(&vcap->vdev);
>>>>    }
>>>> @@ -449,7 +449,7 @@ struct vimc_ent_device *vimc_cap_add(struct vimc_device *vimc,
>>>>        vdev = &vcap->vdev;
>>>>        vdev->device_caps = V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_STREAMING;
>>>>        vdev->entity.ops = &vimc_cap_mops;
>>>> -    vdev->release = vimc_cap_release;
>>>> +    vdev->release = video_device_release_empty;
>>>>        vdev->fops = &vimc_cap_fops;
>>>>        vdev->ioctl_ops = &vimc_cap_ioctl_ops;
>>>>        vdev->lock = &vcap->lock;
>>>> diff --git a/drivers/media/platform/vimc/vimc-common.c b/drivers/media/platform/vimc/vimc-common.c
>>>> index 16ce9f3b7c75..c95c17c048f2 100644
>>>> --- a/drivers/media/platform/vimc/vimc-common.c
>>>> +++ b/drivers/media/platform/vimc/vimc-common.c
>>>> @@ -327,7 +327,6 @@ int vimc_ent_sd_register(struct vimc_ent_device *ved,
>>>>                 u32 function,
>>>>                 u16 num_pads,
>>>>                 struct media_pad *pads,
>>>> -             const struct v4l2_subdev_internal_ops *sd_int_ops,
>>>>                 const struct v4l2_subdev_ops *sd_ops)
>>>>    {
>>>>        int ret;
>>>> @@ -337,7 +336,6 @@ int vimc_ent_sd_register(struct vimc_ent_device *ved,
>>>>          /* Initialize the subdev */
>>>>        v4l2_subdev_init(sd, sd_ops);
>>>> -    sd->internal_ops = sd_int_ops;
>>>>        sd->entity.function = function;
>>>>        sd->entity.ops = &vimc_ent_sd_mops;
>>>>        sd->owner = THIS_MODULE;
>>>> diff --git a/drivers/media/platform/vimc/vimc-common.h b/drivers/media/platform/vimc/vimc-common.h
>>>> index 1b6ef7196f3c..616d5a6b0754 100644
>>>> --- a/drivers/media/platform/vimc/vimc-common.h
>>>> +++ b/drivers/media/platform/vimc/vimc-common.h
>>>> @@ -125,16 +125,18 @@ struct vimc_device {
>>>>     * @name            entity name
>>>>     * @ved                pointer to vimc_ent_device (a node in the
>>>>     *                    topology)
>>>> - * @add                subdev add hook - initializes and registers
>>>> - *                    subdev called from vimc-core
>>>> - * @rm                subdev rm hook - unregisters and frees
>>>> - *                    subdev called from vimc-core
>>>> + * @add                initializes and registers
>>>> + *                    vim entity - called from vimc-core
>>>> + * @unregister            unregisters vimc entity - called from vimc-core
>>>> + * @release            releases vimc entity - called from the v4l2_dev
>>>> + *                    release callback
>>>>     */
>>>
>>> Did you test the suggestion I gave in last patch?
>>> That instead of adding another callback here, to just remove the release functions of the subdevices,
>>> and add a check if the release cb isn't null just before calling it.
>>> With this, the release functions of the video nodes would be called first.
>>>
>> I just tested you suggestion, here is the patch: https://gitlab.collabora.com/dafna/linux/commit/f59bc7c6643ce8f88aa33eb5e9f413a1aca99589
>> I get a kasan report:
>>
>> [   37.736909] BUG: KASAN: use-after-free in v4l2_device_unregister+0xa7/0xf0 [videodev]
>> [   37.738110] Read of size 4 at addr ffff8881eb3f00bc by task bash/227
>> ...
>>
>> What happen is that the function v4l2_device_unregister loops over the subdevices and unregister them:
>>
>>    /* Unregister subdevs */
>>          list_for_each_entry_safe(sd, next, &v4l2_dev->subdevs, list) {
>>                  v4l2_device_unregister_subdev(sd);
>>                  if (sd->flags & V4L2_SUBDEV_FL_IS_I2C)
>>                          v4l2_i2c_subdev_unregister(sd);
>>                  else if (sd->flags & V4L2_SUBDEV_FL_IS_SPI)
>>                          v4l2_spi_subdev_unregister(sd);
>>          }
>>
>> when unregistering the first subdevice it also immediately calls the release callback because no one holds a fh for
>> /dev/v4l2-subdev* , but the release cb releases the memory where the 'sd' in the above loop resides, then when
>> referencing it in sd->flags it is after it is already freed.
> 
> Urgh. That's a bug in that function. I think the if...else if bit can be moved to
> v4l2_subdev_release().
> 
> I'm surprised that this hasn't been seen before.
> I thought that this is not a bug, this happen in vimc only when implementing the release callback
of subdevices which we agreed should not be implemented, or I am missing something?

Dafna

> Regards,
> 
> 	Hans
> 
>>
>> Dafna
>>
>>> I followed the discussion regarding fhs in media node and video, not that I'm against your changes,
>>> but I would like to understand a bit better why the simple fix suggested isn't enough.
>>>
>>> Thanks
>>> Helen
>>>
>>>>    struct vimc_ent_config {
>>>>        const char *name;
>>>>        struct vimc_ent_device *(*add)(struct vimc_device *vimc,
>>>>                           const char *vcfg_name);
>>>> -    void (*rm)(struct vimc_device *vimc, struct vimc_ent_device *ved);
>>>> +    void (*unregister)(struct vimc_ent_device *ved);
>>>> +    void (*release)(struct vimc_ent_device *ved);
>>>>    };
>>>>      /**
>>>> @@ -145,22 +147,23 @@ struct vimc_ent_config {
>>>>     */
>>>>    bool vimc_is_source(struct media_entity *ent);
>>>>    -/* prototypes for vimc_ent_config add and rm hooks */
>>>> +/* prototypes for vimc_ent_config hooks */
>>>>    struct vimc_ent_device *vimc_cap_add(struct vimc_device *vimc,
>>>>                         const char *vcfg_name);
>>>> -void vimc_cap_rm(struct vimc_device *vimc, struct vimc_ent_device *ved);
>>>> +void vimc_cap_unregister(struct vimc_ent_device *ved);
>>>> +void vimc_cap_release(struct vimc_ent_device *ved);
>>>>      struct vimc_ent_device *vimc_deb_add(struct vimc_device *vimc,
>>>>                         const char *vcfg_name);
>>>> -void vimc_deb_rm(struct vimc_device *vimc, struct vimc_ent_device *ved);
>>>> +void vimc_deb_release(struct vimc_ent_device *ved);
>>>>      struct vimc_ent_device *vimc_sca_add(struct vimc_device *vimc,
>>>>                         const char *vcfg_name);
>>>> -void vimc_sca_rm(struct vimc_device *vimc, struct vimc_ent_device *ved);
>>>> +void vimc_sca_release(struct vimc_ent_device *ved);
>>>>      struct vimc_ent_device *vimc_sen_add(struct vimc_device *vimc,
>>>>                         const char *vcfg_name);
>>>> -void vimc_sen_rm(struct vimc_device *vimc, struct vimc_ent_device *ved);
>>>> +void vimc_sen_release(struct vimc_ent_device *ved);
>>>>      /**
>>>>     * vimc_pix_map_by_index - get vimc_pix_map struct by its index
>>>> @@ -195,7 +198,6 @@ const struct vimc_pix_map *vimc_pix_map_by_pixelformat(u32 pixelformat);
>>>>     * @num_pads:    number of pads to initialize
>>>>     * @pads:    the array of pads of the entity, the caller should set the
>>>>            flags of the pads
>>>> - * @sd_int_ops:    pointer to &struct v4l2_subdev_internal_ops
>>>>     * @sd_ops:    pointer to &struct v4l2_subdev_ops.
>>>>     *
>>>>     * Helper function initialize and register the struct vimc_ent_device and struct
>>>> @@ -208,7 +210,6 @@ int vimc_ent_sd_register(struct vimc_ent_device *ved,
>>>>                 u32 function,
>>>>                 u16 num_pads,
>>>>                 struct media_pad *pads,
>>>> -             const struct v4l2_subdev_internal_ops *sd_int_ops,
>>>>                 const struct v4l2_subdev_ops *sd_ops);
>>>>      /**
>>>> diff --git a/drivers/media/platform/vimc/vimc-core.c b/drivers/media/platform/vimc/vimc-core.c
>>>> index 1c55e0382f09..306f9c293628 100644
>>>> --- a/drivers/media/platform/vimc/vimc-core.c
>>>> +++ b/drivers/media/platform/vimc/vimc-core.c
>>>> @@ -48,48 +48,51 @@ static struct vimc_ent_config ent_config[] = {
>>>>        {
>>>>            .name = "Sensor A",
>>>>            .add = vimc_sen_add,
>>>> -        .rm = vimc_sen_rm,
>>>> +        .release = vimc_sen_release,
>>>>        },
>>>>        {
>>>>            .name = "Sensor B",
>>>>            .add = vimc_sen_add,
>>>> -        .rm = vimc_sen_rm,
>>>> +        .release = vimc_sen_release,
>>>>        },
>>>>        {
>>>>            .name = "Debayer A",
>>>>            .add = vimc_deb_add,
>>>> -        .rm = vimc_deb_rm,
>>>> +        .release = vimc_deb_release,
>>>>        },
>>>>        {
>>>>            .name = "Debayer B",
>>>>            .add = vimc_deb_add,
>>>> -        .rm = vimc_deb_rm,
>>>> +        .release = vimc_deb_release,
>>>>        },
>>>>        {
>>>>            .name = "Raw Capture 0",
>>>>            .add = vimc_cap_add,
>>>> -        .rm = vimc_cap_rm,
>>>> +        .unregister = vimc_cap_unregister,
>>>> +        .release = vimc_cap_release,
>>>>        },
>>>>        {
>>>>            .name = "Raw Capture 1",
>>>>            .add = vimc_cap_add,
>>>> -        .rm = vimc_cap_rm,
>>>> +        .unregister = vimc_cap_unregister,
>>>> +        .release = vimc_cap_release,
>>>>        },
>>>>        {
>>>>            /* TODO: change this to vimc-input when it is implemented */
>>>>            .name = "RGB/YUV Input",
>>>>            .add = vimc_sen_add,
>>>> -        .rm = vimc_sen_rm,
>>>> +        .release = vimc_sen_release,
>>>>        },
>>>>        {
>>>>            .name = "Scaler",
>>>>            .add = vimc_sca_add,
>>>> -        .rm = vimc_sca_rm,
>>>> +        .release = vimc_sca_release,
>>>>        },
>>>>        {
>>>>            .name = "RGB/YUV Capture",
>>>>            .add = vimc_cap_add,
>>>> -        .rm = vimc_cap_rm,
>>>> +        .unregister = vimc_cap_unregister,
>>>> +        .release = vimc_cap_release,
>>>>        },
>>>>    };
>>>>    @@ -175,13 +178,33 @@ static int vimc_add_subdevs(struct vimc_device *vimc)
>>>>        return 0;
>>>>    }
>>>>    -static void vimc_rm_subdevs(struct vimc_device *vimc)
>>>> +static void vimc_release_subdevs(struct vimc_device *vimc)
>>>>    {
>>>>        unsigned int i;
>>>>          for (i = 0; i < vimc->pipe_cfg->num_ents; i++)
>>>>            if (vimc->ent_devs[i])
>>>> -            vimc->pipe_cfg->ents[i].rm(vimc, vimc->ent_devs[i]);
>>>> +            vimc->pipe_cfg->ents[i].release(vimc->ent_devs[i]);
>>>> +}
>>>> +
>>>> +static void vimc_unregister_subdevs(struct vimc_device *vimc)
>>>> +{
>>>> +    unsigned int i;
>>>> +
>>>> +    for (i = 0; i < vimc->pipe_cfg->num_ents; i++)
>>>> +        if (vimc->ent_devs[i] && vimc->pipe_cfg->ents[i].unregister)
>>>> +            vimc->pipe_cfg->ents[i].unregister(vimc->ent_devs[i]);
>>>> +}
>>>> +
>>>> +static void vimc_v4l2_dev_release(struct v4l2_device *v4l2_dev)
>>>> +{
>>>> +    struct vimc_device *vimc =
>>>> +        container_of(v4l2_dev, struct vimc_device, v4l2_dev);
>>>> +
>>>> +    vimc_release_subdevs(vimc);
>>>> +    media_device_cleanup(&vimc->mdev);
>>>> +    kfree(vimc->ent_devs);
>>>> +    kfree(vimc);
>>>>    }
>>>>      static int vimc_register_devices(struct vimc_device *vimc)
>>>> @@ -195,7 +218,6 @@ static int vimc_register_devices(struct vimc_device *vimc)
>>>>                "v4l2 device register failed (err=%d)\n", ret);
>>>>            return ret;
>>>>        }
>>>> -
>>>>        /* allocate ent_devs */
>>>>        vimc->ent_devs = kcalloc(vimc->pipe_cfg->num_ents,
>>>>                     sizeof(*vimc->ent_devs), GFP_KERNEL);
>>>> @@ -236,9 +258,9 @@ static int vimc_register_devices(struct vimc_device *vimc)
>>>>      err_mdev_unregister:
>>>>        media_device_unregister(&vimc->mdev);
>>>> -    media_device_cleanup(&vimc->mdev);
>>>>    err_rm_subdevs:
>>>> -    vimc_rm_subdevs(vimc);
>>>> +    vimc_unregister_subdevs(vimc);
>>>> +    vimc_release_subdevs(vimc);
>>>>        kfree(vimc->ent_devs);
>>>>    err_v4l2_unregister:
>>>>        v4l2_device_unregister(&vimc->v4l2_dev);
>>>> @@ -248,11 +270,9 @@ static int vimc_register_devices(struct vimc_device *vimc)
>>>>      static void vimc_unregister(struct vimc_device *vimc)
>>>>    {
>>>> +    vimc_unregister_subdevs(vimc);
>>>>        media_device_unregister(&vimc->mdev);
>>>> -    media_device_cleanup(&vimc->mdev);
>>>>        v4l2_device_unregister(&vimc->v4l2_dev);
>>>> -    kfree(vimc->ent_devs);
>>>> -    kfree(vimc);
>>>>    }
>>>>      static int vimc_probe(struct platform_device *pdev)
>>>> @@ -285,7 +305,12 @@ static int vimc_probe(struct platform_device *pdev)
>>>>            kfree(vimc);
>>>>            return ret;
>>>>        }
>>>> +    /*
>>>> +     * the release cb is set only after successful registration.
>>>> +     * if the registration fails, we release directly from probe
>>>> +     */
>>>>    +    vimc->v4l2_dev.release = vimc_v4l2_dev_release;
>>>>        platform_set_drvdata(pdev, vimc);
>>>>        return 0;
>>>>    }
>>>> @@ -296,8 +321,8 @@ static int vimc_remove(struct platform_device *pdev)
>>>>          dev_dbg(&pdev->dev, "remove");
>>>>    -    vimc_rm_subdevs(vimc);
>>>>        vimc_unregister(vimc);
>>>> +    v4l2_device_put(&vimc->v4l2_dev);
>>>>          return 0;
>>>>    }
>>>> diff --git a/drivers/media/platform/vimc/vimc-debayer.c b/drivers/media/platform/vimc/vimc-debayer.c
>>>> index 34b98b235880..baf6bf9f65b5 100644
>>>> --- a/drivers/media/platform/vimc/vimc-debayer.c
>>>> +++ b/drivers/media/platform/vimc/vimc-debayer.c
>>>> @@ -494,28 +494,16 @@ static const struct v4l2_ctrl_ops vimc_deb_ctrl_ops = {
>>>>        .s_ctrl = vimc_deb_s_ctrl,
>>>>    };
>>>>    -static void vimc_deb_release(struct v4l2_subdev *sd)
>>>> +void vimc_deb_release(struct vimc_ent_device *ved)
>>>>    {
>>>>        struct vimc_deb_device *vdeb =
>>>> -                container_of(sd, struct vimc_deb_device, sd);
>>>> +        container_of(ved, struct vimc_deb_device, ved);
>>>>          v4l2_ctrl_handler_free(&vdeb->hdl);
>>>>        media_entity_cleanup(vdeb->ved.ent);
>>>>        kfree(vdeb);
>>>>    }
>>>>    -static const struct v4l2_subdev_internal_ops vimc_deb_int_ops = {
>>>> -    .release = vimc_deb_release,
>>>> -};
>>>> -
>>>> -void vimc_deb_rm(struct vimc_device *vimc, struct vimc_ent_device *ved)
>>>> -{
>>>> -    struct vimc_deb_device *vdeb;
>>>> -
>>>> -    vdeb = container_of(ved, struct vimc_deb_device, ved);
>>>> -    v4l2_device_unregister_subdev(&vdeb->sd);
>>>> -}
>>>> -
>>>>    static const struct v4l2_ctrl_config vimc_deb_ctrl_class = {
>>>>        .flags = V4L2_CTRL_FLAG_READ_ONLY | V4L2_CTRL_FLAG_WRITE_ONLY,
>>>>        .id = VIMC_CID_VIMC_CLASS,
>>>> @@ -563,8 +551,7 @@ struct vimc_ent_device *vimc_deb_add(struct vimc_device *vimc,
>>>>        ret = vimc_ent_sd_register(&vdeb->ved, &vdeb->sd, v4l2_dev,
>>>>                       vcfg_name,
>>>>                       MEDIA_ENT_F_PROC_VIDEO_PIXEL_ENC_CONV, 2,
>>>> -                   vdeb->pads,
>>>> -                   &vimc_deb_int_ops, &vimc_deb_ops);
>>>> +                   vdeb->pads, &vimc_deb_ops);
>>>>        if (ret)
>>>>            goto err_free_hdl;
>>>>    diff --git a/drivers/media/platform/vimc/vimc-scaler.c b/drivers/media/platform/vimc/vimc-scaler.c
>>>> index cb2dc24c3e59..7521439747c5 100644
>>>> --- a/drivers/media/platform/vimc/vimc-scaler.c
>>>> +++ b/drivers/media/platform/vimc/vimc-scaler.c
>>>> @@ -464,27 +464,15 @@ static void *vimc_sca_process_frame(struct vimc_ent_device *ved,
>>>>        return vsca->src_frame;
>>>>    };
>>>>    -static void vimc_sca_release(struct v4l2_subdev *sd)
>>>> +void vimc_sca_release(struct vimc_ent_device *ved)
>>>>    {
>>>>        struct vimc_sca_device *vsca =
>>>> -                container_of(sd, struct vimc_sca_device, sd);
>>>> +        container_of(ved, struct vimc_sca_device, ved);
>>>>          media_entity_cleanup(vsca->ved.ent);
>>>>        kfree(vsca);
>>>>    }
>>>>    -static const struct v4l2_subdev_internal_ops vimc_sca_int_ops = {
>>>> -    .release = vimc_sca_release,
>>>> -};
>>>> -
>>>> -void vimc_sca_rm(struct vimc_device *vimc, struct vimc_ent_device *ved)
>>>> -{
>>>> -    struct vimc_sca_device *vsca;
>>>> -
>>>> -    vsca = container_of(ved, struct vimc_sca_device, ved);
>>>> -    v4l2_device_unregister_subdev(&vsca->sd);
>>>> -}
>>>> -
>>>>    struct vimc_ent_device *vimc_sca_add(struct vimc_device *vimc,
>>>>                         const char *vcfg_name)
>>>>    {
>>>> @@ -504,8 +492,7 @@ struct vimc_ent_device *vimc_sca_add(struct vimc_device *vimc,
>>>>        ret = vimc_ent_sd_register(&vsca->ved, &vsca->sd, v4l2_dev,
>>>>                       vcfg_name,
>>>>                       MEDIA_ENT_F_PROC_VIDEO_SCALER, 2,
>>>> -                   vsca->pads,
>>>> -                   &vimc_sca_int_ops, &vimc_sca_ops);
>>>> +                   vsca->pads, &vimc_sca_ops);
>>>>        if (ret) {
>>>>            kfree(vsca);
>>>>            return NULL;
>>>> diff --git a/drivers/media/platform/vimc/vimc-sensor.c b/drivers/media/platform/vimc/vimc-sensor.c
>>>> index 9788fe291193..92daee58209e 100644
>>>> --- a/drivers/media/platform/vimc/vimc-sensor.c
>>>> +++ b/drivers/media/platform/vimc/vimc-sensor.c
>>>> @@ -279,10 +279,10 @@ static const struct v4l2_ctrl_ops vimc_sen_ctrl_ops = {
>>>>        .s_ctrl = vimc_sen_s_ctrl,
>>>>    };
>>>>    -static void vimc_sen_release(struct v4l2_subdev *sd)
>>>> +void vimc_sen_release(struct vimc_ent_device *ved)
>>>>    {
>>>>        struct vimc_sen_device *vsen =
>>>> -                container_of(sd, struct vimc_sen_device, sd);
>>>> +        container_of(ved, struct vimc_sen_device, ved);
>>>>          v4l2_ctrl_handler_free(&vsen->hdl);
>>>>        tpg_free(&vsen->tpg);
>>>> @@ -290,18 +290,6 @@ static void vimc_sen_release(struct v4l2_subdev *sd)
>>>>        kfree(vsen);
>>>>    }
>>>>    -static const struct v4l2_subdev_internal_ops vimc_sen_int_ops = {
>>>> -    .release = vimc_sen_release,
>>>> -};
>>>> -
>>>> -void vimc_sen_rm(struct vimc_device *vimc, struct vimc_ent_device *ved)
>>>> -{
>>>> -    struct vimc_sen_device *vsen;
>>>> -
>>>> -    vsen = container_of(ved, struct vimc_sen_device, ved);
>>>> -    v4l2_device_unregister_subdev(&vsen->sd);
>>>> -}
>>>> -
>>>>    /* Image Processing Controls */
>>>>    static const struct v4l2_ctrl_config vimc_sen_ctrl_class = {
>>>>        .flags = V4L2_CTRL_FLAG_READ_ONLY | V4L2_CTRL_FLAG_WRITE_ONLY,
>>>> @@ -365,7 +353,7 @@ struct vimc_ent_device *vimc_sen_add(struct vimc_device *vimc,
>>>>        ret = vimc_ent_sd_register(&vsen->ved, &vsen->sd, v4l2_dev,
>>>>                       vcfg_name,
>>>>                       MEDIA_ENT_F_CAM_SENSOR, 1, &vsen->pad,
>>>> -                   &vimc_sen_int_ops, &vimc_sen_ops);
>>>> +                   &vimc_sen_ops);
>>>>        if (ret)
>>>>            goto err_free_tpg;
>>>>   
>