From: Thomas Zimmermann <tzimmermann@suse.de>
To: saeed.mirzamohammadi@oracle.com, linux-kernel@vger.kernel.org
Cc: linux-fbdev@vger.kernel.org, b.zolnierkie@samsung.com,
jani.nikula@intel.com, daniel.vetter@ffwll.ch,
gustavoars@kernel.org, dri-devel@lists.freedesktop.org,
akpm@linux-foundation.org, rppt@kernel.org
Subject: Re: [PATCH 1/1] video: fbdev: fix divide error in fbcon_switch
Date: Thu, 22 Oct 2020 09:34:11 +0200 [thread overview]
Message-ID: <ad87c5c1-061d-8a81-7b2c-43a8687a464f@suse.de> (raw)
In-Reply-To: <20201021235758.59993-1-saeed.mirzamohammadi@oracle.com>
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 */
>
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer
next prev parent reply other threads:[~2020-10-22 7:34 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-21 23:57 [PATCH 1/1] video: fbdev: fix divide error in fbcon_switch saeed.mirzamohammadi
2020-10-22 0:33 ` Saeed Mirzamohammadi
2020-10-22 7:28 ` Thomas Zimmermann
2020-10-22 7:34 ` Thomas Zimmermann [this message]
2020-10-26 17:00 ` Saeed Mirzamohammadi
2020-10-27 6:22 ` Greg KH
[not found] ` <2DA9AE6D-93D6-4142-9FC4-EEACB92B7203@oracle.com>
2020-10-29 11:03 ` Greg KH
2020-10-29 11:13 ` Jani Nikula
2020-10-29 11:30 ` Greg KH
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=ad87c5c1-061d-8a81-7b2c-43a8687a464f@suse.de \
--to=tzimmermann@suse.de \
--cc=akpm@linux-foundation.org \
--cc=b.zolnierkie@samsung.com \
--cc=daniel.vetter@ffwll.ch \
--cc=dri-devel@lists.freedesktop.org \
--cc=gustavoars@kernel.org \
--cc=jani.nikula@intel.com \
--cc=linux-fbdev@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=rppt@kernel.org \
--cc=saeed.mirzamohammadi@oracle.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).