Re: [patch] Avoid NULL deref in v4l2_device_release (was Re: kernel OOPS when releasing usb webcam (random))

["Tomas M." <tmezzadra@gmail.com>]

Hi Everyone,

Yes, this appears to have fixed the issue.

thanks!

On 10/17/2011 09:19 PM, Frederik Deweerdt wrote:
> [Adding relevant people to CCs]
>
> Hi Tomas,
>
> On Mon, Oct 17, 2011 at 07:48:34PM -0300, Tomas M. wrote:
>> im getting the following null pointer dereference from time to time
>> when releasing a usb camera.
>>
> [...]
>> BUG: unable to handle kernel NULL pointer dereference at 0000006c
>> IP: [<f90be6c2>] v4l2_device_release+0xa2/0xf0 [videodev]
>> *pde = 00000000
>> Oops: 0000 [#1] PREEMPT SMP
>> Modules linked in: fuse arc4 rt73usb rt2x00usb rt2x00lib mac80211
>> cfg80211 rfkill gspca_zc3xx gspca_main videodev joydev
>> snd_hda_codec_si3054 sg 8139too snd_hda_codec_realtek firewire_ohci
>> firewire_core mmc_core snd_hda_intel snd_hda_codec snd_hwdep snd_pcm
>> snd_timer snd soundcore mii crc_itu_t snd_page_alloc iTCO_wdt
>> iTCO_vendor_support i2c_i801 evdev psmouse thermal battery serio_raw
>> ac cpufreq_ondemand acpi_cpufreq freq_table processor mperf usbhid
>> hid ext3 jbd mbcache sd_mod sr_mod cdrom pata_acpi uhci_hcd ata_piix
>> ehci_hcd libata scsi_mod usbcore [last unloaded: sdhci]
>>
>> Pid: 171, comm: khubd Not tainted 3.1.0-rc9 #66 Everex Systems, Inc.
>> Everex StepNote Series/Everex StepNote Series
>> EIP: 0060:[<f90be6c2>] EFLAGS: 00010292 CPU: 0
>> EIP is at v4l2_device_release+0xa2/0xf0 [videodev]
>> EAX: 00000000 EBX: f5636004 ECX: 00000000 EDX: 00000000
>> ESI: f5636000 EDI: 00000000 EBP: f563600c ESP: f5627e38
>>   DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
>> Process khubd (pid: 171, ti=f5626000 task=f554dc00 task.ti=f5626000)
>> Stack:
>>   ef000480 c1433780 f5474b00 c12343f8 f54e7e1c 00000000 c114737a f563600c
>>   f5636028 c114605d f5636028 c1146020 f91512d4 00000000 c114737a f54e7e1c
>>   f54e7e00 f81623f4 f56d4000 f54e7e1c f91512d4 f56d4064 00000001 c12373b7
>> Call Trace:
>>   [<c12343f8>] ? device_release+0x18/0x80
>>   [<c114737a>] ? kref_put+0x2a/0x60
>>   [<c114605d>] ? kobject_release+0x3d/0xa0
>>   [<c1146020>] ? kobject_del+0x30/0x30
>>   [<c114737a>] ? kref_put+0x2a/0x60
>>   [<f81623f4>] ? usb_unbind_interface+0x34/0x130 [usbcore]
>>   [<c12373b7>] ? __device_release_driver+0x57/0xb0
>>   [<c123742d>] ? device_release_driver+0x1d/0x30
>>   [<c1236fc2>] ? bus_remove_device+0x72/0x90
>>   [<c12350bf>] ? device_del+0xdf/0x150
>>   [<f8160591>] ? usb_disable_device+0x81/0x180 [usbcore]
>>   [<f8159b3b>] ? usb_disconnect+0x8b/0x110 [usbcore]
>>   [<f815b76c>] ? hub_thread+0x97c/0x1180 [usbcore]
>>   [<c102d80b>] ? pick_next_task_fair+0x8b/0xe0
>>   [<c1052600>] ? abort_exclusive_wait+0x90/0x90
>>   [<f815adf0>] ? usb_remote_wakeup+0x40/0x40 [usbcore]
>>   [<c1052029>] ? kthread+0x69/0x70
>>   [<c1051fc0>] ? kthread_worker_fn+0x150/0x150
>>   [<c130d8be>] ? kernel_thread_helper+0x6/0xd
>> Code: 83 94 01 00 00 c7 83 60 01 00 00 00 00 00 00 0f b7 93 9c 01 00
>> 00 c1 e0 05 f0 0f b3 90 c0 e7 0c f9 b8 20 e1 0c f9 e8 4e cf 24 c8
>> <8b>  57 6c 89 f0 85 d2 74 25 ff 93 c8 01 00 00 85 ff 74 21 89 f8
>> EIP: [<f90be6c2>] v4l2_device_release+0xa2/0xf0 [videodev] SS:ESP
>> 0068:f5627e38
>> CR2: 000000000000006c
>> ---[ end trace 39522f0f1757c8f8 ]---
>
> The trace hints at a v4l2 being NULL in a newly introduced
> v4l2_dev->release check. Attached patch below.
>
> Regards,
> Frederik
>
> [media] v4l: Avoid NULL pointer dereference
>
> 8280b662df96f4172c4972b14a4aec0daf272b8f introduced a potential NULL
> deref in the case v4l2_dev is NULL.
>
> Reported-by: Tomas M.<tmezzadra@gmail.com>
> Signed-off-by: Frederik Deweerdt<frederik.deweerdt@xprog.eu>
>
> diff --git a/drivers/media/video/v4l2-dev.c b/drivers/media/video/v4l2-dev.c
> index d721565..5c0fa64 100644
> --- a/drivers/media/video/v4l2-dev.c
> +++ b/drivers/media/video/v4l2-dev.c
> @@ -181,7 +181,7 @@ static void v4l2_device_release(struct device *cd)
>   	 * TODO: In the long run all drivers that use v4l2_device should use the
>   	 * v4l2_device release callback. This check will then be unnecessary.
>   	 */
> -	if (v4l2_dev->release == NULL)
> +	if (v4l2_dev != NULL&&  v4l2_dev->release == NULL)
>   		v4l2_dev = NULL;
>
>   	/* Release video_device and perform other
>