Re: [PATCH] usb: gadget: uvc: Fix ERR_PTR dereference in uvc_v4l2.c

[Michael Grzeschik <mgr@pengutronix.de>]

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Hi Laurent,

On Fri, Aug 02, 2024 at 09:18:41PM +0300, Laurent Pinchart wrote:
>Hi Abhishek,
>
>(CC'ing Michael Grzeschik)
>
>Thank you for the patch.
>
>On Fri, Aug 02, 2024 at 11:32:47PM +0530, Abhishek Tamboli wrote:
>> Fix potential dereferencing of ERR_PTR() in find_format_by_pix()
>> and uvc_v4l2_enum_format().
>>
>> Fix the following smatch errors:
>>
>> drivers/usb/gadget/function/uvc_v4l2.c:124 find_format_by_pix()
>> error: 'fmtdesc' dereferencing possible ERR_PTR()
>> drivers/usb/gadget/function/uvc_v4l2.c:392 uvc_v4l2_enum_format()
>> error: 'fmtdesc' dereferencing possible ERR_PTR()
>>
>> Signed-off-by: Abhishek Tamboli <abhishektamboli9@gmail.com>
>> ---
>>  drivers/usb/gadget/function/uvc_v4l2.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/usb/gadget/function/uvc_v4l2.c b/drivers/usb/gadget/function/uvc_v4l2.c
>> index a024aecb76dc..9dd602a742c4 100644
>> --- a/drivers/usb/gadget/function/uvc_v4l2.c
>> +++ b/drivers/usb/gadget/function/uvc_v4l2.c
>> @@ -121,6 +121,9 @@ static struct uvcg_format *find_format_by_pix(struct uvc_device *uvc,
>>  	list_for_each_entry(format, &uvc->header->formats, entry) {
>>  		const struct uvc_format_desc *fmtdesc = to_uvc_format(format->fmt);
>>
>> +		if (IS_ERR(fmtdesc))
>> +			continue;
>> +
>>  		if (fmtdesc->fcc == pixelformat) {
>>  			uformat = format->fmt;
>>  			break;
>> @@ -389,6 +392,9 @@ uvc_v4l2_enum_format(struct file *file, void *fh, struct v4l2_fmtdesc *f)
>>  		return -EINVAL;
>>
>>  	fmtdesc = to_uvc_format(uformat);
>> +	if (IS_ERR(fmtdesc))
>> +		return -EINVAL;
>> +
>>  	f->pixelformat = fmtdesc->fcc;
>>
>>  	return 0;
>
>Michael, you authored this, I'll let you review the patch and decide if
>this is a false positive.

Since the following patch was applied,

https://lore.kernel.org/all/20240221-uvc-gadget-configfs-guid-v1-1-f0678ca62ebb@pengutronix.de/

the issue is technically impossible to happen.

However the patch I mentioned was only applied recently and in all older
kernels someone could add a format into configfs that is not part of
uvc_format_desc from drivers/media/common/uvc.c and therefor can run
into the issue.

As this will also not hurt the current kernel I would like the patch
to be applied with the Tag:

Fixes: 588b9e8560 (usb: gadget: uvc: add v4l2 enumeration api calls)

Thanks,
Michael

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