2024-03-19 08:15:19

by Roman Smirnov

Subject: [PATCH v3] fbmon: prevent division by zero in fb_videomode_from_videomode()

The expression htotal * vtotal can have a zero value on
overflow. It is necessary to prevent division by zero like in
fb_var_to_videomode().

Found by Linux Verification Center (linuxtesting.org) with Svace.

Signed-off-by: Roman Smirnov <[email protected]>
Reviewed-by: Sergey Shtylyov <[email protected]>
---
V1 -> V2: Replaced the code of the first version with a check.
V2 -> V3: Replaced the code of the second version with a zero check

drivers/video/fbdev/core/fbmon.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/core/fbmon.c b/drivers/video/fbdev/core/fbmon.c
index 79e5bfbdd34c..ca946919d962 100644
--- a/drivers/video/fbdev/core/fbmon.c
+++ b/drivers/video/fbdev/core/fbmon.c
@@ -1344,7 +1344,7 @@ int fb_videomode_from_videomode(const struct videomode *vm,
vtotal = vm->vactive + vm->vfront_porch + vm->vback_porch +
vm->vsync_len;
/* prevent division by zero */
- if (htotal && vtotal) {
+ if (htotal && vtotal && (htotal * vtotal)) {
fbmode->refresh = vm->pixelclock / (htotal * vtotal);
/* a mode must have htotal and vtotal != 0 or it is invalid */
} else {
--
2.34.1

2024-03-19 12:23:28

by Helge Deller

Subject: Re: [PATCH v3] fbmon: prevent division by zero in fb_videomode_from_videomode()

On 3/19/24 09:13, Roman Smirnov wrote:
> The expression htotal * vtotal can have a zero value on
> overflow. It is necessary to prevent division by zero like in
> fb_var_to_videomode().
>
> Found by Linux Verification Center (linuxtesting.org) with Svace.
>
> Signed-off-by: Roman Smirnov <[email protected]>
> Reviewed-by: Sergey Shtylyov <[email protected]>
> ---
> V1 -> V2: Replaced the code of the first version with a check.
> V2 -> V3: Replaced the code of the second version with a zero check
>
> drivers/video/fbdev/core/fbmon.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/video/fbdev/core/fbmon.c b/drivers/video/fbdev/core/fbmon.c
> index 79e5bfbdd34c..ca946919d962 100644
> --- a/drivers/video/fbdev/core/fbmon.c
> +++ b/drivers/video/fbdev/core/fbmon.c
> @@ -1344,7 +1344,7 @@ int fb_videomode_from_videomode(const struct videomode *vm,
> vtotal = vm->vactive + vm->vfront_porch + vm->vback_porch +
> vm->vsync_len;
> /* prevent division by zero */
> - if (htotal && vtotal) {
> + if (htotal && vtotal && (htotal * vtotal)) {
> fbmode->refresh = vm->pixelclock / (htotal * vtotal);

I modified your patch like this:
..
- if (htotal && vtotal) {
- fbmode->refresh = vm->pixelclock / (htotal * vtotal);
+ total = htotal * vtotal;
+ if (total) {
+ fbmode->refresh = vm->pixelclock / total;

and added it to the fbdev git tree.
https://git.kernel.org/pub/scm/linux/kernel/git/deller/linux-fbdev.git/commit/?h=for-next

Thanks,
Helge