diff mbox series

[1/1] video: fbdev: fix divide error in fbcon_switch

Message ID 20201021235758.59993-1-saeed.mirzamohammadi@oracle.com (mailing list archive)
State New, archived
Headers show
Series [1/1] video: fbdev: fix divide error in fbcon_switch | expand

Commit Message

Saeed Mirzamohammadi Oct. 21, 2020, 11:57 p.m. UTC
From: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>

This patch fixes the issue due to:

[   89.572883] divide_error: 0000 [#1] SMP KASAN PTI
[   89.572897] CPU: 3 PID: 16083 Comm: repro Not tainted 5.9.0-rc7.20200930.rc1.allarch-19-g3e32d0d.syzk #5
[   89.572902] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.5.1 01/01/2011
[   89.572934] RIP: 0010:cirrusfb_check_var+0x84/0x1260

The error happens when the pixels value is calculated before performing the sanity checks on bits_per_pixel.
A bits_per_pixel set to zero causes divide by zero error.

This patch moves the calculation after the sanity check.

Signed-off-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
Tested-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
---
 drivers/video/fbdev/cirrusfb.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Saeed Mirzamohammadi Oct. 22, 2020, 12:33 a.m. UTC | #1
Attached the Syzkaller C reproducer.
> On Oct 21, 2020, at 4:57 PM, saeed.mirzamohammadi@oracle.com wrote:
> 
> From: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
> 
> This patch fixes the issue due to:
> 
> [   89.572883] divide_error: 0000 [#1] SMP KASAN PTI
> [   89.572897] CPU: 3 PID: 16083 Comm: repro Not tainted 5.9.0-rc7.20200930.rc1.allarch-19-g3e32d0d.syzk #5
> [   89.572902] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.5.1 01/01/2011
> [   89.572934] RIP: 0010:cirrusfb_check_var+0x84/0x1260
> 
> The error happens when the pixels value is calculated before performing the sanity checks on bits_per_pixel.
> A bits_per_pixel set to zero causes divide by zero error.
> 
> This patch moves the calculation after the sanity check.
> 
> Signed-off-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
> Tested-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
> ---
> drivers/video/fbdev/cirrusfb.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/video/fbdev/cirrusfb.c b/drivers/video/fbdev/cirrusfb.c
> index 15a9ee7cd734..a7749101b094 100644
> --- a/drivers/video/fbdev/cirrusfb.c
> +++ b/drivers/video/fbdev/cirrusfb.c
> @@ -531,7 +531,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var,
> {
> 	int yres;
> 	/* memory size in pixels */
> -	unsigned pixels = info->screen_size * 8 / var->bits_per_pixel;
> +	unsigned int pixels;
> 	struct cirrusfb_info *cinfo = info->par;
> 
> 	switch (var->bits_per_pixel) {
> @@ -573,6 +573,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var,
> 		return -EINVAL;
> 	}
> 
> +	pixels = info->screen_size * 8 / var->bits_per_pixel;
> 	if (var->xres_virtual < var->xres)
> 		var->xres_virtual = var->xres;
> 	/* use highest possible virtual resolution */
> -- 
> 2.27.0
>
Thomas Zimmermann Oct. 22, 2020, 7:28 a.m. UTC | #2
Hi

On 22.10.20 01:57, saeed.mirzamohammadi@oracle.com wrote:
> From: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
> 
> This patch fixes the issue due to:
> 
> [   89.572883] divide_error: 0000 [#1] SMP KASAN PTI
> [   89.572897] CPU: 3 PID: 16083 Comm: repro Not tainted 5.9.0-rc7.20200930.rc1.allarch-19-g3e32d0d.syzk #5
> [   89.572902] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.5.1 01/01/2011
> [   89.572934] RIP: 0010:cirrusfb_check_var+0x84/0x1260
> 
> The error happens when the pixels value is calculated before performing the sanity checks on bits_per_pixel.
> A bits_per_pixel set to zero causes divide by zero error.
> 
> This patch moves the calculation after the sanity check.
> 
> Signed-off-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
> Tested-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>

Looks good, thanks a lot. I'll add the patch to drm-misc-next

Reviewed-by: Thomas Zimemrmann <tzimmermann@suse.de>

Best regards
Thomas

> ---
>  drivers/video/fbdev/cirrusfb.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/video/fbdev/cirrusfb.c b/drivers/video/fbdev/cirrusfb.c
> index 15a9ee7cd734..a7749101b094 100644
> --- a/drivers/video/fbdev/cirrusfb.c
> +++ b/drivers/video/fbdev/cirrusfb.c
> @@ -531,7 +531,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var,
>  {
>  	int yres;
>  	/* memory size in pixels */
> -	unsigned pixels = info->screen_size * 8 / var->bits_per_pixel;
> +	unsigned int pixels;
>  	struct cirrusfb_info *cinfo = info->par;
>  
>  	switch (var->bits_per_pixel) {
> @@ -573,6 +573,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var,
>  		return -EINVAL;
>  	}
>  
> +	pixels = info->screen_size * 8 / var->bits_per_pixel;
>  	if (var->xres_virtual < var->xres)
>  		var->xres_virtual = var->xres;
>  	/* use highest possible virtual resolution */
>
Thomas Zimmermann Oct. 22, 2020, 7:34 a.m. UTC | #3
Hi

On 22.10.20 01:57, saeed.mirzamohammadi@oracle.com wrote:
> From: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
> 
> This patch fixes the issue due to:
> 
> [   89.572883] divide_error: 0000 [#1] SMP KASAN PTI
> [   89.572897] CPU: 3 PID: 16083 Comm: repro Not tainted 5.9.0-rc7.20200930.rc1.allarch-19-g3e32d0d.syzk #5
> [   89.572902] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.5.1 01/01/2011
> [   89.572934] RIP: 0010:cirrusfb_check_var+0x84/0x1260

BTW, if you run qemu with cirrus, there's also a DRM driver named
cirrus.ko. Might be a better choice than the old fbdev driver. If you
just care about qemu, but not the actual graphics device, take a look at

  https://www.kraxel.org/blog/2014/10/qemu-using-cirrus-considered-harmful/

Anyway, thanks for your patch.

Best regards
Thomas

> 
> The error happens when the pixels value is calculated before performing the sanity checks on bits_per_pixel.
> A bits_per_pixel set to zero causes divide by zero error.
> 
> This patch moves the calculation after the sanity check.
> 
> Signed-off-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
> Tested-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
> ---
>  drivers/video/fbdev/cirrusfb.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/video/fbdev/cirrusfb.c b/drivers/video/fbdev/cirrusfb.c
> index 15a9ee7cd734..a7749101b094 100644
> --- a/drivers/video/fbdev/cirrusfb.c
> +++ b/drivers/video/fbdev/cirrusfb.c
> @@ -531,7 +531,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var,
>  {
>  	int yres;
>  	/* memory size in pixels */
> -	unsigned pixels = info->screen_size * 8 / var->bits_per_pixel;
> +	unsigned int pixels;
>  	struct cirrusfb_info *cinfo = info->par;
>  
>  	switch (var->bits_per_pixel) {
> @@ -573,6 +573,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var,
>  		return -EINVAL;
>  	}
>  
> +	pixels = info->screen_size * 8 / var->bits_per_pixel;
>  	if (var->xres_virtual < var->xres)
>  		var->xres_virtual = var->xres;
>  	/* use highest possible virtual resolution */
>
Saeed Mirzamohammadi Oct. 26, 2020, 5 p.m. UTC | #4
Thanks, adding stable.

Saeed

> On Oct 22, 2020, at 12:34 AM, Thomas Zimmermann <tzimmermann@suse.de> wrote:
> 
> Hi
> 
> On 22.10.20 01:57, saeed.mirzamohammadi@oracle.com wrote:
>> From: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
>> 
>> This patch fixes the issue due to:
>> 
>> [   89.572883] divide_error: 0000 [#1] SMP KASAN PTI
>> [   89.572897] CPU: 3 PID: 16083 Comm: repro Not tainted 5.9.0-rc7.20200930.rc1.allarch-19-g3e32d0d.syzk #5
>> [   89.572902] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.5.1 01/01/2011
>> [   89.572934] RIP: 0010:cirrusfb_check_var+0x84/0x1260
> 
> BTW, if you run qemu with cirrus, there's also a DRM driver named
> cirrus.ko. Might be a better choice than the old fbdev driver. If you
> just care about qemu, but not the actual graphics device, take a look at
> 
>  https://urldefense.com/v3/__https://www.kraxel.org/blog/2014/10/qemu-using-cirrus-considered-harmful/__;!!GqivPVa7Brio!LmgeM-pVBVH80uVELF1P1nBGAbAlhvnxKKE_ZrEc9d76AznvAAgP1FAp3_zNa2frKaIUZteK$ 
> 
> Anyway, thanks for your patch.
> 
> Best regards
> Thomas
> 
>> 
>> The error happens when the pixels value is calculated before performing the sanity checks on bits_per_pixel.
>> A bits_per_pixel set to zero causes divide by zero error.
>> 
>> This patch moves the calculation after the sanity check.
>> 
>> Signed-off-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
>> Tested-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
>> ---
>> drivers/video/fbdev/cirrusfb.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/video/fbdev/cirrusfb.c b/drivers/video/fbdev/cirrusfb.c
>> index 15a9ee7cd734..a7749101b094 100644
>> --- a/drivers/video/fbdev/cirrusfb.c
>> +++ b/drivers/video/fbdev/cirrusfb.c
>> @@ -531,7 +531,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var,
>> {
>> 	int yres;
>> 	/* memory size in pixels */
>> -	unsigned pixels = info->screen_size * 8 / var->bits_per_pixel;
>> +	unsigned int pixels;
>> 	struct cirrusfb_info *cinfo = info->par;
>> 
>> 	switch (var->bits_per_pixel) {
>> @@ -573,6 +573,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var,
>> 		return -EINVAL;
>> 	}
>> 
>> +	pixels = info->screen_size * 8 / var->bits_per_pixel;
>> 	if (var->xres_virtual < var->xres)
>> 		var->xres_virtual = var->xres;
>> 	/* use highest possible virtual resolution */
>> 
> 
> -- 
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Felix Imendörffer
Greg Kroah-Hartman Oct. 27, 2020, 6:22 a.m. UTC | #5
On Mon, Oct 26, 2020 at 10:00:11AM -0700, Saeed Mirzamohammadi wrote:
> Thanks, adding stable.

Why?  What are we supposed to do with this?
Greg Kroah-Hartman Oct. 29, 2020, 11:03 a.m. UTC | #6
On Tue, Oct 27, 2020 at 10:12:49AM -0700, Saeed Mirzamohammadi wrote:
> Hi Greg,
> 
> Sorry for the confusion. I’m requesting stable maintainers to cherry-pick this patch into stable 5.4 and 5.8.
> commit cc07057c7c88fb8eff3b1991131ded0f0bcfa7e3
> Author: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
> Date:   Wed Oct 21 16:57:58 2020 -0700
> 
>     video: fbdev: fix divide error in fbcon_switch

I do not see that commit in Linus's tree, do you?

confused,

greg k-h
Jani Nikula Oct. 29, 2020, 11:13 a.m. UTC | #7
On Thu, 29 Oct 2020, Greg KH <gregkh@linuxfoundation.org> wrote:
> On Tue, Oct 27, 2020 at 10:12:49AM -0700, Saeed Mirzamohammadi wrote:
>> Hi Greg,
>> 
>> Sorry for the confusion. I’m requesting stable maintainers to cherry-pick this patch into stable 5.4 and 5.8.
>> commit cc07057c7c88fb8eff3b1991131ded0f0bcfa7e3
>> Author: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
>> Date:   Wed Oct 21 16:57:58 2020 -0700
>> 
>>     video: fbdev: fix divide error in fbcon_switch
>
> I do not see that commit in Linus's tree, do you?

It's in drm-misc-next, IIUC heading for Linus' tree in the next merge
window in 6-8 weeks. Which is to say this should probably have been
applied to drm-misc-fixes branch heading for v5.10-rcX, with a Cc:
stable tag, to begin with.

BR,
Jani.
Greg Kroah-Hartman Oct. 29, 2020, 11:30 a.m. UTC | #8
On Thu, Oct 29, 2020 at 01:13:01PM +0200, Jani Nikula wrote:
> On Thu, 29 Oct 2020, Greg KH <gregkh@linuxfoundation.org> wrote:
> > On Tue, Oct 27, 2020 at 10:12:49AM -0700, Saeed Mirzamohammadi wrote:
> >> Hi Greg,
> >> 
> >> Sorry for the confusion. I’m requesting stable maintainers to cherry-pick this patch into stable 5.4 and 5.8.
> >> commit cc07057c7c88fb8eff3b1991131ded0f0bcfa7e3
> >> Author: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
> >> Date:   Wed Oct 21 16:57:58 2020 -0700
> >> 
> >>     video: fbdev: fix divide error in fbcon_switch
> >
> > I do not see that commit in Linus's tree, do you?
> 
> It's in drm-misc-next, IIUC heading for Linus' tree in the next merge
> window in 6-8 weeks. Which is to say this should probably have been
> applied to drm-misc-fixes branch heading for v5.10-rcX, with a Cc:
> stable tag, to begin with.

Ok, nothing I can do with this now, please email stable@vger.kernel.org
when it hits Linus's tree and we can take it then.

Saeed, please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

thanks,

greg k-h
diff mbox series

Patch

diff --git a/drivers/video/fbdev/cirrusfb.c b/drivers/video/fbdev/cirrusfb.c
index 15a9ee7cd734..a7749101b094 100644
--- a/drivers/video/fbdev/cirrusfb.c
+++ b/drivers/video/fbdev/cirrusfb.c
@@ -531,7 +531,7 @@  static int cirrusfb_check_var(struct fb_var_screeninfo *var,
 {
 	int yres;
 	/* memory size in pixels */
-	unsigned pixels = info->screen_size * 8 / var->bits_per_pixel;
+	unsigned int pixels;
 	struct cirrusfb_info *cinfo = info->par;
 
 	switch (var->bits_per_pixel) {
@@ -573,6 +573,7 @@  static int cirrusfb_check_var(struct fb_var_screeninfo *var,
 		return -EINVAL;
 	}
 
+	pixels = info->screen_size * 8 / var->bits_per_pixel;
 	if (var->xres_virtual < var->xres)
 		var->xres_virtual = var->xres;
 	/* use highest possible virtual resolution */