[PATCH 0/3] Fix bugs in *_set_par() caused by user input

[PATCH 0/3] Fix bugs in *_set_par() caused by user input

[Zheyu Ma]

In the function *_set_par(), the value of 'screen_size' is
calculated by the user input. If the user provides the improper value,
the value of 'screen_size' may larger than 'info->screen_size', which
may cause a bug in the memset_io().

Zheyu Ma (3):
  video: fbdev: vt8623fb: Check the size of screen before memset_io()
  video: fbdev: arkfb: Check the size of screen before memset_io()
  video: fbdev: s3fb: Check the size of screen before memset_io()

 drivers/video/fbdev/arkfb.c    | 2 ++
 drivers/video/fbdev/s3fb.c     | 2 ++
 drivers/video/fbdev/vt8623fb.c | 2 ++
 3 files changed, 6 insertions(+)

-- 
2.25.1

[PATCH 1/3] video: fbdev: vt8623fb: Check the size of screen before memset_io()

[Zheyu Ma]

In the function vt8623fb_set_par(), the value of 'screen_size' is
calculated by the user input. If the user provides the improper value,
the value of 'screen_size' may larger than 'info->screen_size', which
may cause the following bug:

[  583.339036] BUG: unable to handle page fault for address: ffffc90005000000
[  583.339049] #PF: supervisor write access in kernel mode
[  583.339052] #PF: error_code(0x0002) - not-present page
[  583.339074] RIP: 0010:memset_orig+0x33/0xb0
[  583.339110] Call Trace:
[  583.339118]  vt8623fb_set_par+0x11cd/0x21e0
[  583.339146]  fb_set_var+0x604/0xeb0
[  583.339181]  do_fb_ioctl+0x234/0x670
[  583.339209]  fb_ioctl+0xdd/0x130

Fix the this by checking the value of 'screen_size' before memset_io().

Fixes: 558b7bd86c32 ("vt8623fb: new framebuffer driver for VIA VT8623")
Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
---
 drivers/video/fbdev/vt8623fb.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/video/fbdev/vt8623fb.c b/drivers/video/fbdev/vt8623fb.c
index a92a8c670cf0..4274c6efb249 100644
--- a/drivers/video/fbdev/vt8623fb.c
+++ b/drivers/video/fbdev/vt8623fb.c
@@ -507,6 +507,8 @@ static int vt8623fb_set_par(struct fb_info *info)
 			 (info->var.vmode & FB_VMODE_DOUBLE) ? 2 : 1, 1,
 			 1, info->node);
 
+	if (screen_size > info->screen_size)
+		screen_size = info->screen_size;
 	memset_io(info->screen_base, 0x00, screen_size);
 
 	/* Device and screen back on */
-- 
2.25.1

[PATCH 2/3] video: fbdev: arkfb: Check the size of screen before memset_io()

[Zheyu Ma]

In the function arkfb_set_par(), the value of 'screen_size' is
calculated by the user input. If the user provides the improper value,
the value of 'screen_size' may larger than 'info->screen_size', which
may cause the following bug:

[  659.399066] BUG: unable to handle page fault for address: ffffc90003000000
[  659.399077] #PF: supervisor write access in kernel mode
[  659.399079] #PF: error_code(0x0002) - not-present page
[  659.399094] RIP: 0010:memset_orig+0x33/0xb0
[  659.399116] Call Trace:
[  659.399122]  arkfb_set_par+0x143f/0x24c0
[  659.399130]  fb_set_var+0x604/0xeb0
[  659.399161]  do_fb_ioctl+0x234/0x670
[  659.399189]  fb_ioctl+0xdd/0x130

Fix the this by checking the value of 'screen_size' before memset_io().

Fixes: 681e14730c73 ("arkfb: new framebuffer driver for ARK Logic cards")
Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
---
 drivers/video/fbdev/arkfb.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/video/fbdev/arkfb.c b/drivers/video/fbdev/arkfb.c
index eb3e47c58c5f..de4002914f9e 100644
--- a/drivers/video/fbdev/arkfb.c
+++ b/drivers/video/fbdev/arkfb.c
@@ -792,6 +792,8 @@ static int arkfb_set_par(struct fb_info *info)
 	value = ((value * hmul / hdiv) / 8) - 5;
 	vga_wcrt(par->state.vgabase, 0x42, (value + 1) / 2);
 
+	if (screen_size > info->screen_size)
+		screen_size = info->screen_size;
 	memset_io(info->screen_base, 0x00, screen_size);
 	/* Device and screen back on */
 	svga_wcrt_mask(par->state.vgabase, 0x17, 0x80, 0x80);
-- 
2.25.1

[PATCH 3/3] video: fbdev: s3fb: Check the size of screen before memset_io()

[Zheyu Ma]

In the function s3fb_set_par(), the value of 'screen_size' is
calculated by the user input. If the user provides the improper value,
the value of 'screen_size' may larger than 'info->screen_size', which
may cause the following bug:

[   54.083733] BUG: unable to handle page fault for address: ffffc90003000000
[   54.083742] #PF: supervisor write access in kernel mode
[   54.083744] #PF: error_code(0x0002) - not-present page
[   54.083760] RIP: 0010:memset_orig+0x33/0xb0
[   54.083782] Call Trace:
[   54.083788]  s3fb_set_par+0x1ec6/0x4040
[   54.083806]  fb_set_var+0x604/0xeb0
[   54.083836]  do_fb_ioctl+0x234/0x670

Fix the this by checking the value of 'screen_size' before memset_io().

Fixes: a268422de8bf ("[PATCH] fbdev driver for S3 Trio/Virge")
Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
---
 drivers/video/fbdev/s3fb.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/video/fbdev/s3fb.c b/drivers/video/fbdev/s3fb.c
index b93c8eb02336..5069f6f67923 100644
--- a/drivers/video/fbdev/s3fb.c
+++ b/drivers/video/fbdev/s3fb.c
@@ -905,6 +905,8 @@ static int s3fb_set_par(struct fb_info *info)
 	value = clamp((htotal + hsstart + 1) / 2 + 2, hsstart + 4, htotal + 1);
 	svga_wcrt_multi(par->state.vgabase, s3_dtpc_regs, value);
 
+	if (screen_size > info->screen_size)
+		screen_size = info->screen_size;
 	memset_io(info->screen_base, 0x00, screen_size);
 	/* Device and screen back on */
 	svga_wcrt_mask(par->state.vgabase, 0x17, 0x80, 0x80);
-- 
2.25.1

Re: [PATCH 0/3] Fix bugs in *_set_par() caused by user input

[Ondrej Zajicek]

On Thu, Aug 04, 2022 at 08:41:22PM +0800, Zheyu Ma wrote:
> In the function *_set_par(), the value of 'screen_size' is
> calculated by the user input. If the user provides the improper value,
> the value of 'screen_size' may larger than 'info->screen_size', which
> may cause a bug in the memset_io().

Hi

I did not saw fbdev code in years, but should not this be already checked
by *_check_var() ?

arkfb_check_var():

	...
	/* Check whether have enough memory */
	mem = ((var->bits_per_pixel * var->xres_virtual) >> 3) * var->yres_virtual;
	if (mem > info->screen_size)
	...

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago@crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."

Re: [PATCH 0/3] Fix bugs in *_set_par() caused by user input

[Zheyu Ma]

Hello,

On Thu, Aug 4, 2022 at 10:43 PM Ondrej Zajicek <santiago@crfreenet.org> wrote:
>
> On Thu, Aug 04, 2022 at 08:41:22PM +0800, Zheyu Ma wrote:
> > In the function *_set_par(), the value of 'screen_size' is
> > calculated by the user input. If the user provides the improper value,
> > the value of 'screen_size' may larger than 'info->screen_size', which
> > may cause a bug in the memset_io().
>
> Hi
>
> I did not saw fbdev code in years, but should not this be already checked
> by *_check_var() ?
>
> arkfb_check_var():
>
>         ...
>         /* Check whether have enough memory */
>         mem = ((var->bits_per_pixel * var->xres_virtual) >> 3) * var->yres_virtual;
>         if (mem > info->screen_size)
>         ...

Thanks for the reminder. But since the user can control all the
parameters of the ioctl system call, it is possible to assign
'var->bits_per_pixel' to be 0 and thus 'mem' will be 0, bypassing this
check. And in *_set_par(), when 'var->bits_per_pixel' is 0,
'screen_size' will be calculated as follows:

    u32 bpp = info->var.bits_per_pixel;
    if (bpp != 0) {
        ...
    } else {
        ...
        screen_size = (info->var.xres_virtual * info->var.yres_virtual) / 64;
    }

resulting in a very large value.

regards,

Zheyu Ma

Re: [PATCH 0/3] Fix bugs in *_set_par() caused by user input

[Helge Deller]

On 8/4/22 14:41, Zheyu Ma wrote:
> In the function *_set_par(), the value of 'screen_size' is
> calculated by the user input. If the user provides the improper value,
> the value of 'screen_size' may larger than 'info->screen_size', which
> may cause a bug in the memset_io().
>
> Zheyu Ma (3):
>   video: fbdev: vt8623fb: Check the size of screen before memset_io()
>   video: fbdev: arkfb: Check the size of screen before memset_io()
>   video: fbdev: s3fb: Check the size of screen before memset_io()

applied all 3 patches to fbdev git tree.

Thanks!
Helge

>
>  drivers/video/fbdev/arkfb.c    | 2 ++
>  drivers/video/fbdev/s3fb.c     | 2 ++
>  drivers/video/fbdev/vt8623fb.c | 2 ++
>  3 files changed, 6 insertions(+)
>