linux-kernel - Re: [PATCH v2] video: imsttfb: Fix use after free bug in imsttfb_probe due to lack of error-handling of init

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Date:   Mon, 22 May 2023 20:02:27 +0200
From:   Helge Deller <deller@....de>
To:     Michal Koutný <mkoutny@...e.com>,
        Zheng Wang <zyytlz.wz@....com>
Cc:     alex000young@...il.com, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, hackerzheng666@...il.com,
        dri-devel@...ts.freedesktop.org, javierm@...hat.com,
        1395428693sheep@...il.com, tzimmermann@...e.de
Subject: Re: [PATCH v2] video: imsttfb: Fix use after free bug in
 imsttfb_probe due to lack of error-handling of init_imstt

Hi Michal,

On 5/22/23 17:36, Michal Koutný wrote:
> On Thu, Apr 27, 2023 at 11:08:41AM +0800, Zheng Wang <zyytlz.wz@....com> wrote:
>>   static int imsttfb_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>> @@ -1529,10 +1530,10 @@ static int imsttfb_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>>   	if (!par->cmap_regs)
>>   		goto error;
>>   	info->pseudo_palette = par->palette;
>> -	init_imstt(info);
>> -
>> -	pci_set_drvdata(pdev, info);
>> -	return 0;
>> +	ret = init_imstt(info);
>> +	if (!ret)
>> +		pci_set_drvdata(pdev, info);
>> +	return ret;
>>
>>   error:
>>   	if (par->dc_regs)
>
> This part caught my eye -- shouldn't the -ENODEV from init_imstt go
> through the standard error with proper cleanup? (It seems like a leak
> from my 30000 ft view, i.e. not sure about imsttfb_{probe,remove}
> pairing.)

Yes, you seem to be right.

> Shouldn't there be something like the diff below on top of the existing code?

Yes, but ....


> Regards,
> Michal
>
> diff --git a/drivers/video/fbdev/imsttfb.c b/drivers/video/fbdev/imsttfb.c
> index 975dd682fae4..a116ac8ca020 100644
> --- a/drivers/video/fbdev/imsttfb.c
> +++ b/drivers/video/fbdev/imsttfb.c
> @@ -1419,7 +1419,6 @@ static int init_imstt(struct fb_info *info)
>   	if ((info->var.xres * info->var.yres) * (info->var.bits_per_pixel >> 3) > info->fix.smem_len
>   	    || !(compute_imstt_regvals(par, info->var.xres, info->var.yres))) {
>   		printk("imsttfb: %ux%ux%u not supported\n", info->var.xres, info->var.yres, info->var.bits_per_pixel);
> -		framebuffer_release(info);
>   		return -ENODEV;
>   	}
>
> @@ -1455,7 +1454,6 @@ static int init_imstt(struct fb_info *info)
>   	fb_alloc_cmap(&info->cmap, 0, 0);
>
>   	if (register_framebuffer(info) < 0) {
> -		framebuffer_release(info);

That's ^^^  ok, but I think a
	fb_dealloc_cmap()
is missing here ...

... and in the error path of imsttfb_probe() ....

>   		return -ENODEV;
>   	}
>
> @@ -1531,8 +1529,10 @@ static int imsttfb_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>   		goto error;
>   	info->pseudo_palette = par->palette;
>   	ret = init_imstt(info);
> -	if (!ret)
> -		pci_set_drvdata(pdev, info);
> +	if (ret)
> +		goto error;
> +
> +	pci_set_drvdata(pdev, info);
>   	return ret;
>
>   error:

Would you mind sending a proper patch?

Thanks for noticing!
Helge