Re: [PATCH 4.4 28/31] video: hgafb: fix potential NULL pointer dereference

Greg Kroah-Hartman
2021-05-26T07:13:13Z

On Tue, May 25, 2021 at 06:06:15PM -0300, Igor Torrente wrote:
> Hi Pavel,
>
> On 5/25/21 5:47 PM, Pavel Machek wrote:
> > Hi!
> >
> > > From: Igor Matheus Andrade Torrente <igormtorrente@gmail.com>
> > >
> > > commit dc13cac4862cc68ec74348a80b6942532b7735fa upstream.
> > >
> > > The return of ioremap if not checked, and can lead to a NULL to be
> > > assigned to hga_vram. Potentially leading to a NULL pointer
> > > dereference.
> > >
> > > The fix adds code to deal with this case in the error label and
> > > changes how the hgafb_probe handles the return of hga_card_detect.
> >
> > This will break hgafb completely, right? And crash system without hga
> > card as a bonus.
> >
> > > +++ b/drivers/video/fbdev/hgafb.c
> > > @@ -285,6 +285,8 @@ static int hga_card_detect(void)
> > > hga_vram_len = 0x08000;
> > > hga_vram = ioremap(0xb0000, hga_vram_len);
> > > + if (!hga_vram)
> > > + return -ENOMEM;
> > > if (request_region(0x3b0, 12, "hgafb"))
> > > release_io_ports = 1;
> > > @@ -344,13 +346,18 @@ static int hga_card_detect(void)
> > > hga_type_name = "Hercules";
> > > break;
> > > }
> > > - return 1;
> > > + return 0;
> >
> > Ok, so calling convention is now "0 means detected".
> >
> >
> > > @@ -548,13 +555,11 @@ static struct fb_ops hgafb_ops = {
> > > static int hgafb_probe(struct platform_device *pdev)
> > > {
> > > struct fb_info *info;
> > > + int ret;
> > ...
> > > + ret = hga_card_detect();
> > > + if (!ret)
> > > + return ret;
> > > printk(KERN_INFO "hgafb: %s with %ldK of memory detected.\n",
> > > hga_type_name, hga_vram_len/1024);
> > >
> >
> > If the card is detected, 0 is returned, !0 is true, and we abort
> > detection....
>
> Yes, you are right! There's a patch that fixes it:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git/commit/?h=char-misc-linus&id=02625c965239b71869326dd0461615f27307ecb3
>
> As far as I know, this patch should be queue up soon to all stable branches.
>
> Greg should have more details about it.

Good catch, I'll go queue that up now, thanks.

greg k-h