[PATCH] media: em28xx: fix corrupted list

[PATCH] media: em28xx: fix corrupted list

[Pavel Skripkin]

Syzbot reported corrupted list in em28xx driver. The problem was in
non-reinitialized lists on disconnect. Since all 2 lists are global
variables and driver can be connected and disconnected many times we
should call INIT_LIST_HEAD() in .disconnect method to prevent corrupted
list entries.

Fixes: 1a23f81b7dc3 ("V4L/DVB (9979): em28xx: move usb probe code to a proper place")
Reported-by: syzbot+a6969ef522a36d3344c9@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
---
 drivers/media/usb/em28xx/em28xx-cards.c | 2 ++
 drivers/media/usb/em28xx/em28xx-core.c  | 6 ++++++
 drivers/media/usb/em28xx/em28xx.h       | 1 +
 3 files changed, 9 insertions(+)

diff --git a/drivers/media/usb/em28xx/em28xx-cards.c b/drivers/media/usb/em28xx/em28xx-cards.c
index ba9292e2a587..8b1ff79c37a0 100644
--- a/drivers/media/usb/em28xx/em28xx-cards.c
+++ b/drivers/media/usb/em28xx/em28xx-cards.c
@@ -4148,6 +4148,8 @@ static void em28xx_usb_disconnect(struct usb_interface *intf)
 		dev->dev_next = NULL;
 	}
 	kref_put(&dev->ref, em28xx_free_device);
+
+	em28xx_reset_lists();
 }
 
 static int em28xx_usb_suspend(struct usb_interface *intf,
diff --git a/drivers/media/usb/em28xx/em28xx-core.c b/drivers/media/usb/em28xx/em28xx-core.c
index 584fa400cd7d..03970ed00dba 100644
--- a/drivers/media/usb/em28xx/em28xx-core.c
+++ b/drivers/media/usb/em28xx/em28xx-core.c
@@ -1131,6 +1131,12 @@ void em28xx_init_extension(struct em28xx *dev)
 	mutex_unlock(&em28xx_devlist_mutex);
 }
 
+void em28xx_reset_lists(void)
+{
+	INIT_LIST_HEAD(&em28xx_devlist);
+	INIT_LIST_HEAD(&em28xx_extension_devlist);
+}
+
 void em28xx_close_extension(struct em28xx *dev)
 {
 	const struct em28xx_ops *ops = NULL;
diff --git a/drivers/media/usb/em28xx/em28xx.h b/drivers/media/usb/em28xx/em28xx.h
index ab167cd1f400..73caaaa398d3 100644
--- a/drivers/media/usb/em28xx/em28xx.h
+++ b/drivers/media/usb/em28xx/em28xx.h
@@ -835,6 +835,7 @@ void em28xx_stop_urbs(struct em28xx *dev);
 int em28xx_set_mode(struct em28xx *dev, enum em28xx_mode set_mode);
 int em28xx_gpio_set(struct em28xx *dev, const struct em28xx_reg_seq *gpio);
 int em28xx_register_extension(struct em28xx_ops *dev);
+void em28xx_reset_lists(void);
 void em28xx_unregister_extension(struct em28xx_ops *dev);
 void em28xx_init_extension(struct em28xx *dev);
 void em28xx_close_extension(struct em28xx *dev);
-- 
2.32.0

Re: [PATCH] media: em28xx: fix corrupted list

[Hans Verkuil]

On 06/07/2021 16:50, Pavel Skripkin wrote:
> Syzbot reported corrupted list in em28xx driver. The problem was in
> non-reinitialized lists on disconnect. Since all 2 lists are global
> variables and driver can be connected and disconnected many times we
> should call INIT_LIST_HEAD() in .disconnect method to prevent corrupted
> list entries.
> 
> Fixes: 1a23f81b7dc3 ("V4L/DVB (9979): em28xx: move usb probe code to a proper place")
> Reported-by: syzbot+a6969ef522a36d3344c9@syzkaller.appspotmail.com
> Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
> ---
>  drivers/media/usb/em28xx/em28xx-cards.c | 2 ++
>  drivers/media/usb/em28xx/em28xx-core.c  | 6 ++++++
>  drivers/media/usb/em28xx/em28xx.h       | 1 +
>  3 files changed, 9 insertions(+)
> 
> diff --git a/drivers/media/usb/em28xx/em28xx-cards.c b/drivers/media/usb/em28xx/em28xx-cards.c
> index ba9292e2a587..8b1ff79c37a0 100644
> --- a/drivers/media/usb/em28xx/em28xx-cards.c
> +++ b/drivers/media/usb/em28xx/em28xx-cards.c
> @@ -4148,6 +4148,8 @@ static void em28xx_usb_disconnect(struct usb_interface *intf)
>  		dev->dev_next = NULL;
>  	}
>  	kref_put(&dev->ref, em28xx_free_device);
> +
> +	em28xx_reset_lists();
>  }
>  
>  static int em28xx_usb_suspend(struct usb_interface *intf,
> diff --git a/drivers/media/usb/em28xx/em28xx-core.c b/drivers/media/usb/em28xx/em28xx-core.c
> index 584fa400cd7d..03970ed00dba 100644
> --- a/drivers/media/usb/em28xx/em28xx-core.c
> +++ b/drivers/media/usb/em28xx/em28xx-core.c
> @@ -1131,6 +1131,12 @@ void em28xx_init_extension(struct em28xx *dev)
>  	mutex_unlock(&em28xx_devlist_mutex);
>  }
>  
> +void em28xx_reset_lists(void)
> +{
> +	INIT_LIST_HEAD(&em28xx_devlist);
> +	INIT_LIST_HEAD(&em28xx_extension_devlist);

This needs a mutex_lock(&em28xx_devlist_mutex);

But actually, I don't think this is right: if there are multiple em28xx
devices, then I think if you disconnect one, then the other is - with this
code - also removed from the list.

Can you give a link to the actual syzbot bug? I'm not at all sure you are
fixing the right thing here.

Regards,

	Hans

> +}
> +
>  void em28xx_close_extension(struct em28xx *dev)
>  {
>  	const struct em28xx_ops *ops = NULL;
> diff --git a/drivers/media/usb/em28xx/em28xx.h b/drivers/media/usb/em28xx/em28xx.h
> index ab167cd1f400..73caaaa398d3 100644
> --- a/drivers/media/usb/em28xx/em28xx.h
> +++ b/drivers/media/usb/em28xx/em28xx.h
> @@ -835,6 +835,7 @@ void em28xx_stop_urbs(struct em28xx *dev);
>  int em28xx_set_mode(struct em28xx *dev, enum em28xx_mode set_mode);
>  int em28xx_gpio_set(struct em28xx *dev, const struct em28xx_reg_seq *gpio);
>  int em28xx_register_extension(struct em28xx_ops *dev);
> +void em28xx_reset_lists(void);
>  void em28xx_unregister_extension(struct em28xx_ops *dev);
>  void em28xx_init_extension(struct em28xx *dev);
>  void em28xx_close_extension(struct em28xx *dev);
> 

Re: [PATCH] media: em28xx: fix corrupted list

[Pavel Skripkin]

On Tue, 20 Jul 2021 14:13:13 +0200
Hans Verkuil <hverkuil@xs4all.nl> wrote:

> On 06/07/2021 16:50, Pavel Skripkin wrote:
> > Syzbot reported corrupted list in em28xx driver. The problem was in
> > non-reinitialized lists on disconnect. Since all 2 lists are global
> > variables and driver can be connected and disconnected many times we
> > should call INIT_LIST_HEAD() in .disconnect method to prevent
> > corrupted list entries.
> > 
> > Fixes: 1a23f81b7dc3 ("V4L/DVB (9979): em28xx: move usb probe code
> > to a proper place") Reported-by:
> > syzbot+a6969ef522a36d3344c9@syzkaller.appspotmail.com
> > Signed-off-by: Pavel Skripkin <paskripkin@gmail.com> ---
> >  drivers/media/usb/em28xx/em28xx-cards.c | 2 ++
> >  drivers/media/usb/em28xx/em28xx-core.c  | 6 ++++++
> >  drivers/media/usb/em28xx/em28xx.h       | 1 +
> >  3 files changed, 9 insertions(+)
> > 
> > diff --git a/drivers/media/usb/em28xx/em28xx-cards.c
> > b/drivers/media/usb/em28xx/em28xx-cards.c index
> > ba9292e2a587..8b1ff79c37a0 100644 ---
> > a/drivers/media/usb/em28xx/em28xx-cards.c +++
> > b/drivers/media/usb/em28xx/em28xx-cards.c @@ -4148,6 +4148,8 @@
> > static void em28xx_usb_disconnect(struct usb_interface *intf)
> > dev->dev_next = NULL; }
> >  	kref_put(&dev->ref, em28xx_free_device);
> > +
> > +	em28xx_reset_lists();
> >  }
> >  
> >  static int em28xx_usb_suspend(struct usb_interface *intf,
> > diff --git a/drivers/media/usb/em28xx/em28xx-core.c
> > b/drivers/media/usb/em28xx/em28xx-core.c index
> > 584fa400cd7d..03970ed00dba 100644 ---
> > a/drivers/media/usb/em28xx/em28xx-core.c +++
> > b/drivers/media/usb/em28xx/em28xx-core.c @@ -1131,6 +1131,12 @@
> > void em28xx_init_extension(struct em28xx *dev)
> > mutex_unlock(&em28xx_devlist_mutex); }
> >  
> > +void em28xx_reset_lists(void)
> > +{
> > +	INIT_LIST_HEAD(&em28xx_devlist);
> > +	INIT_LIST_HEAD(&em28xx_extension_devlist);
> 
> This needs a mutex_lock(&em28xx_devlist_mutex);
> 
> But actually, I don't think this is right: if there are multiple
> em28xx devices, then I think if you disconnect one, then the other is
> - with this code - also removed from the list.
> 
> Can you give a link to the actual syzbot bug? I'm not at all sure you
> are fixing the right thing here.

Hi, Hans!

I guess, I missed my coffee that morning, sorry :) This patch looks
complety wrong, of course.

I've took a close look at this bug one more time, and I found the true
root case of this bug.

If em28xx dev has dev_next pointer we need to close dev->next extension
on disconnect to avoid UAF and corrupted list bug. So, something like
this should work:

diff --git a/drivers/media/usb/em28xx/em28xx-cards.c b/drivers/media/usb/em28xx/em28xx-cards.c
index c1e0dccb7408..d56b040e1bd7 100644
--- a/drivers/media/usb/em28xx/em28xx-cards.c
+++ b/drivers/media/usb/em28xx/em28xx-cards.c
@@ -4139,8 +4139,10 @@ static void em28xx_usb_disconnect(struct usb_interface *intf)
 
 	em28xx_close_extension(dev);
 
-	if (dev->dev_next)
+	if (dev->dev_next) {
 		em28xx_release_resources(dev->dev_next);
+		em28xx_close_extension(dev->dev_next);
+	}
 	em28xx_release_resources(dev);
 
 	if (dev->dev_next) {

How to You feel about it? I am going to send this patch for syzbot
testing


Syzbot link:
https://syzkaller.appspot.com/bug?id=3609bbf45bf63a8f6032f330eb3d34f51cc81493


Again, sorry for v1 patch, I don't know how I came up with this fix :(
 


With regards,
Pavel Skripkin

Re: [PATCH] media: em28xx: fix corrupted list

[Hans Verkuil]

On 21/07/2021 14:21, Pavel Skripkin wrote:
> On Tue, 20 Jul 2021 14:13:13 +0200
> Hans Verkuil <hverkuil@xs4all.nl> wrote:
> 
>> On 06/07/2021 16:50, Pavel Skripkin wrote:
>>> Syzbot reported corrupted list in em28xx driver. The problem was in
>>> non-reinitialized lists on disconnect. Since all 2 lists are global
>>> variables and driver can be connected and disconnected many times we
>>> should call INIT_LIST_HEAD() in .disconnect method to prevent
>>> corrupted list entries.
>>>
>>> Fixes: 1a23f81b7dc3 ("V4L/DVB (9979): em28xx: move usb probe code
>>> to a proper place") Reported-by:
>>> syzbot+a6969ef522a36d3344c9@syzkaller.appspotmail.com
>>> Signed-off-by: Pavel Skripkin <paskripkin@gmail.com> ---
>>>  drivers/media/usb/em28xx/em28xx-cards.c | 2 ++
>>>  drivers/media/usb/em28xx/em28xx-core.c  | 6 ++++++
>>>  drivers/media/usb/em28xx/em28xx.h       | 1 +
>>>  3 files changed, 9 insertions(+)
>>>
>>> diff --git a/drivers/media/usb/em28xx/em28xx-cards.c
>>> b/drivers/media/usb/em28xx/em28xx-cards.c index
>>> ba9292e2a587..8b1ff79c37a0 100644 ---
>>> a/drivers/media/usb/em28xx/em28xx-cards.c +++
>>> b/drivers/media/usb/em28xx/em28xx-cards.c @@ -4148,6 +4148,8 @@
>>> static void em28xx_usb_disconnect(struct usb_interface *intf)
>>> dev->dev_next = NULL; }
>>>  	kref_put(&dev->ref, em28xx_free_device);
>>> +
>>> +	em28xx_reset_lists();
>>>  }
>>>  
>>>  static int em28xx_usb_suspend(struct usb_interface *intf,
>>> diff --git a/drivers/media/usb/em28xx/em28xx-core.c
>>> b/drivers/media/usb/em28xx/em28xx-core.c index
>>> 584fa400cd7d..03970ed00dba 100644 ---
>>> a/drivers/media/usb/em28xx/em28xx-core.c +++
>>> b/drivers/media/usb/em28xx/em28xx-core.c @@ -1131,6 +1131,12 @@
>>> void em28xx_init_extension(struct em28xx *dev)
>>> mutex_unlock(&em28xx_devlist_mutex); }
>>>  
>>> +void em28xx_reset_lists(void)
>>> +{
>>> +	INIT_LIST_HEAD(&em28xx_devlist);
>>> +	INIT_LIST_HEAD(&em28xx_extension_devlist);
>>
>> This needs a mutex_lock(&em28xx_devlist_mutex);
>>
>> But actually, I don't think this is right: if there are multiple
>> em28xx devices, then I think if you disconnect one, then the other is
>> - with this code - also removed from the list.
>>
>> Can you give a link to the actual syzbot bug? I'm not at all sure you
>> are fixing the right thing here.
> 
> Hi, Hans!
> 
> I guess, I missed my coffee that morning, sorry :) This patch looks
> complety wrong, of course.
> 
> I've took a close look at this bug one more time, and I found the true
> root case of this bug.
> 
> If em28xx dev has dev_next pointer we need to close dev->next extension
> on disconnect to avoid UAF and corrupted list bug. So, something like
> this should work:
> 
> diff --git a/drivers/media/usb/em28xx/em28xx-cards.c b/drivers/media/usb/em28xx/em28xx-cards.c
> index c1e0dccb7408..d56b040e1bd7 100644
> --- a/drivers/media/usb/em28xx/em28xx-cards.c
> +++ b/drivers/media/usb/em28xx/em28xx-cards.c
> @@ -4139,8 +4139,10 @@ static void em28xx_usb_disconnect(struct usb_interface *intf)
>  
>  	em28xx_close_extension(dev);
>  
> -	if (dev->dev_next)
> +	if (dev->dev_next) {
>  		em28xx_release_resources(dev->dev_next);
> +		em28xx_close_extension(dev->dev_next);
> +	}
>  	em28xx_release_resources(dev);
>  
>  	if (dev->dev_next) {
> 
> How to You feel about it? I am going to send this patch for syzbot
> testing

That looks a lot saner :-)

> 
> 
> Syzbot link:
> https://syzkaller.appspot.com/bug?id=3609bbf45bf63a8f6032f330eb3d34f51cc81493
> 
> 
> Again, sorry for v1 patch, I don't know how I came up with this fix :(

No problem, just post a v2 if syzbot passes.

Regards,

	Hans

>  
> 
> 
> With regards,
> Pavel Skripkin
> 

[PATCH v2] media: em28xx: add missing em28xx_close_extension

[Pavel Skripkin]

If em28xx dev has ->dev_next pointer, we need to delete dev_next list node
from em28xx_extension_devlist on disconnect to avoid UAF bugs and
corrupted list bugs, since driver frees this pointer on disconnect.

Fixes: 1a23f81b7dc3 ("V4L/DVB (9979): em28xx: move usb probe code to a proper place")
Reported-and-tested-by: syzbot+a6969ef522a36d3344c9@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
---

Changes in v2:
	Previous patch was completely broken. I've done some debugging
	again and found true root case of the reported bug.

---
 drivers/media/usb/em28xx/em28xx-cards.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/media/usb/em28xx/em28xx-cards.c b/drivers/media/usb/em28xx/em28xx-cards.c
index c1e0dccb7408..d56b040e1bd7 100644
--- a/drivers/media/usb/em28xx/em28xx-cards.c
+++ b/drivers/media/usb/em28xx/em28xx-cards.c
@@ -4139,8 +4139,10 @@ static void em28xx_usb_disconnect(struct usb_interface *intf)
 
 	em28xx_close_extension(dev);
 
-	if (dev->dev_next)
+	if (dev->dev_next) {
 		em28xx_release_resources(dev->dev_next);
+		em28xx_close_extension(dev->dev_next);
+	}
 	em28xx_release_resources(dev);
 
 	if (dev->dev_next) {
-- 
2.32.0

Re: [PATCH v2] media: em28xx: add missing em28xx_close_extension

[Hans Verkuil]

On 21/07/2021 21:43, Pavel Skripkin wrote:
> If em28xx dev has ->dev_next pointer, we need to delete dev_next list node
> from em28xx_extension_devlist on disconnect to avoid UAF bugs and
> corrupted list bugs, since driver frees this pointer on disconnect.
> 
> Fixes: 1a23f81b7dc3 ("V4L/DVB (9979): em28xx: move usb probe code to a proper place")
> Reported-and-tested-by: syzbot+a6969ef522a36d3344c9@syzkaller.appspotmail.com
> Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
> ---
> 
> Changes in v2:
> 	Previous patch was completely broken. I've done some debugging
> 	again and found true root case of the reported bug.
> 
> ---
>  drivers/media/usb/em28xx/em28xx-cards.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/usb/em28xx/em28xx-cards.c b/drivers/media/usb/em28xx/em28xx-cards.c
> index c1e0dccb7408..d56b040e1bd7 100644
> --- a/drivers/media/usb/em28xx/em28xx-cards.c
> +++ b/drivers/media/usb/em28xx/em28xx-cards.c
> @@ -4139,8 +4139,10 @@ static void em28xx_usb_disconnect(struct usb_interface *intf)
>  
>  	em28xx_close_extension(dev);
>  
> -	if (dev->dev_next)
> +	if (dev->dev_next) {
>  		em28xx_release_resources(dev->dev_next);
> +		em28xx_close_extension(dev->dev_next);

Wouldn't it be better to swap these two?

That order is also used for em28xx_close_extension(dev) and em28xx_release_resources(dev).

You do need to store dev->dev_next in a temp variable, though.

Regards,

	Hans

> +	}
>  	em28xx_release_resources(dev);
>  
>  	if (dev->dev_next) {
> 

Re: [PATCH v2] media: em28xx: add missing em28xx_close_extension

[Pavel Skripkin]

On Thu, 29 Jul 2021 11:45:19 +0200
Hans Verkuil <hverkuil@xs4all.nl> wrote:

> On 21/07/2021 21:43, Pavel Skripkin wrote:
> > If em28xx dev has ->dev_next pointer, we need to delete dev_next
> > list node from em28xx_extension_devlist on disconnect to avoid UAF
> > bugs and corrupted list bugs, since driver frees this pointer on
> > disconnect.
> > 
> > Fixes: 1a23f81b7dc3 ("V4L/DVB (9979): em28xx: move usb probe code
> > to a proper place") Reported-and-tested-by:
> > syzbot+a6969ef522a36d3344c9@syzkaller.appspotmail.com
> > Signed-off-by: Pavel Skripkin <paskripkin@gmail.com> ---
> > 
> > Changes in v2:
> > 	Previous patch was completely broken. I've done some
> > debugging again and found true root case of the reported bug.
> > 
> > ---
> >  drivers/media/usb/em28xx/em28xx-cards.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/media/usb/em28xx/em28xx-cards.c
> > b/drivers/media/usb/em28xx/em28xx-cards.c index
> > c1e0dccb7408..d56b040e1bd7 100644 ---
> > a/drivers/media/usb/em28xx/em28xx-cards.c +++
> > b/drivers/media/usb/em28xx/em28xx-cards.c @@ -4139,8 +4139,10 @@
> > static void em28xx_usb_disconnect(struct usb_interface *intf) 
> >  	em28xx_close_extension(dev);
> >  
> > -	if (dev->dev_next)
> > +	if (dev->dev_next) {
> >  		em28xx_release_resources(dev->dev_next);
> > +		em28xx_close_extension(dev->dev_next);
> 
> Wouldn't it be better to swap these two?
> 
> That order is also used for em28xx_close_extension(dev) and
> em28xx_release_resources(dev).
> 
> You do need to store dev->dev_next in a temp variable, though.
> 

Hi, Hans!

I don't understand why I need to store dev->dev_next in a temp
variable. I don't see code in em28xx_release_resources() or
em28xx_close_extension() that zeroes this pointer.



With regards,
Pavel Skripkin

Re: [PATCH v2] media: em28xx: add missing em28xx_close_extension

[Hans Verkuil]

On 29/07/2021 14:45, Pavel Skripkin wrote:
> On Thu, 29 Jul 2021 11:45:19 +0200
> Hans Verkuil <hverkuil@xs4all.nl> wrote:
> 
>> On 21/07/2021 21:43, Pavel Skripkin wrote:
>>> If em28xx dev has ->dev_next pointer, we need to delete dev_next
>>> list node from em28xx_extension_devlist on disconnect to avoid UAF
>>> bugs and corrupted list bugs, since driver frees this pointer on
>>> disconnect.
>>>
>>> Fixes: 1a23f81b7dc3 ("V4L/DVB (9979): em28xx: move usb probe code
>>> to a proper place") Reported-and-tested-by:
>>> syzbot+a6969ef522a36d3344c9@syzkaller.appspotmail.com
>>> Signed-off-by: Pavel Skripkin <paskripkin@gmail.com> ---
>>>
>>> Changes in v2:
>>> 	Previous patch was completely broken. I've done some
>>> debugging again and found true root case of the reported bug.
>>>
>>> ---
>>>  drivers/media/usb/em28xx/em28xx-cards.c | 4 +++-
>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/media/usb/em28xx/em28xx-cards.c
>>> b/drivers/media/usb/em28xx/em28xx-cards.c index
>>> c1e0dccb7408..d56b040e1bd7 100644 ---
>>> a/drivers/media/usb/em28xx/em28xx-cards.c +++
>>> b/drivers/media/usb/em28xx/em28xx-cards.c @@ -4139,8 +4139,10 @@
>>> static void em28xx_usb_disconnect(struct usb_interface *intf) 
>>>  	em28xx_close_extension(dev);
>>>  
>>> -	if (dev->dev_next)
>>> +	if (dev->dev_next) {
>>>  		em28xx_release_resources(dev->dev_next);
>>> +		em28xx_close_extension(dev->dev_next);
>>
>> Wouldn't it be better to swap these two?
>>
>> That order is also used for em28xx_close_extension(dev) and
>> em28xx_release_resources(dev).
>>
>> You do need to store dev->dev_next in a temp variable, though.
>>
> 
> Hi, Hans!
> 
> I don't understand why I need to store dev->dev_next in a temp
> variable. I don't see code in em28xx_release_resources() or
> em28xx_close_extension() that zeroes this pointer.

Apologies for the confusion, just ignore that bit. I misunderstood
what dev_next was for.

So check if swapping these two lines passes syzbot, and then that's
the final version.

Regards,

	Hans

> 
> 
> 
> With regards,
> Pavel Skripkin
> 
> 

[PATCH v3] media: em28xx: add missing em28xx_close_extension

[Pavel Skripkin]

If em28xx dev has ->dev_next pointer, we need to delete ->dev_next list
node from em28xx_extension_devlist on disconnect to avoid UAF bugs and
corrupted list bugs, since driver frees this pointer on disconnect.

Fixes: 1a23f81b7dc3 ("V4L/DVB (9979): em28xx: move usb probe code to a proper place")
Reported-and-tested-by: syzbot+a6969ef522a36d3344c9@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
---

Changes in v3:
	Changed order of em28xx_close_extension() and
	em28xx_release_resources() as Hans suggested

Changes in v2:
	Previous patch was completely broken. I've done some debugging
	again and found true root case of the reported bug.

---
 drivers/media/usb/em28xx/em28xx-cards.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/media/usb/em28xx/em28xx-cards.c b/drivers/media/usb/em28xx/em28xx-cards.c
index c1e0dccb7408..948e22e29b42 100644
--- a/drivers/media/usb/em28xx/em28xx-cards.c
+++ b/drivers/media/usb/em28xx/em28xx-cards.c
@@ -4139,8 +4139,11 @@ static void em28xx_usb_disconnect(struct usb_interface *intf)
 
 	em28xx_close_extension(dev);
 
-	if (dev->dev_next)
+	if (dev->dev_next) {
+		em28xx_close_extension(dev->dev_next);
 		em28xx_release_resources(dev->dev_next);
+	}
+
 	em28xx_release_resources(dev);
 
 	if (dev->dev_next) {
-- 
2.32.0