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

[Helge Deller <deller@gmx.de>]

On 4/27/23 05:08, Zheng Wang wrote:
> A use-after-free bug may occur if init_imstt invokes framebuffer_release
> and free the info ptr. The caller, imsttfb_probe didn't notice that and
> still keep the ptr as private data in pdev.
>
> If we remove the driver which will call imsttfb_remove to make cleanup,
> UAF happens.
>
> Fix it by return error code if bad case happens in init_imstt.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Zheng Wang <zyytlz.wz@163.com>

applied.
Thanks!
Helge

> ---
> v2:
> - add return error code in another location.
> ---
>   drivers/video/fbdev/imsttfb.c | 15 ++++++++-------
>   1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/video/fbdev/imsttfb.c b/drivers/video/fbdev/imsttfb.c
> index bea45647184e..975dd682fae4 100644
> --- a/drivers/video/fbdev/imsttfb.c
> +++ b/drivers/video/fbdev/imsttfb.c
> @@ -1347,7 +1347,7 @@ static const struct fb_ops imsttfb_ops = {
>   	.fb_ioctl 	= imsttfb_ioctl,
>   };
>
> -static void init_imstt(struct fb_info *info)
> +static int init_imstt(struct fb_info *info)
>   {
>   	struct imstt_par *par = info->par;
>   	__u32 i, tmp, *ip, *end;
> @@ -1420,7 +1420,7 @@ static void init_imstt(struct fb_info *info)
>   	    || !(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;
> +		return -ENODEV;
>   	}
>
>   	sprintf(info->fix.id, "IMS TT (%s)", par->ramdac == IBM ? "IBM" : "TVP");
> @@ -1456,12 +1456,13 @@ static void init_imstt(struct fb_info *info)
>
>   	if (register_framebuffer(info) < 0) {
>   		framebuffer_release(info);
> -		return;
> +		return -ENODEV;
>   	}
>
>   	tmp = (read_reg_le32(par->dc_regs, SSTATUS) & 0x0f00) >> 8;
>   	fb_info(info, "%s frame buffer; %uMB vram; chip version %u\n",
>   		info->fix.id, info->fix.smem_len >> 20, tmp);
> +	return 0;
>   }
>
>   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)