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

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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@xxxxxx>
Reviewed-by: Sergey Shtylyov <s.shtylyov@xxxxxx>
---
  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




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