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

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

[Roman Smirnov]

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 <r.smirnov@omp.ru>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
---
 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

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

[Helge Deller]

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 <r.smirnov@omp.ru>
> Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
> ---
>   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