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Subject: Re: [PATCH] media: em28xx: fix corrupted list
To:     Pavel Skripkin <paskripkin@gmail.com>, mchehab@kernel.org
Cc:     linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzbot+a6969ef522a36d3344c9@syzkaller.appspotmail.com
References: <20210706145025.25776-1-paskripkin@gmail.com>
From:   Hans Verkuil <hverkuil@xs4all.nl>
Message-ID: <c6bb9cd0-2a8d-99c3-a14d-51c6364ba92d@xs4all.nl>
Date:   Tue, 20 Jul 2021 14:13:13 +0200
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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);
>