[PATCH] fbdev: i740: Fix potential divide by zero

Variable var->pixclock can be set by user. In case it equals to
zero, divide by zero would occur in 4 switch branches in
i740fb_decode_var.
Similar crashes have happened in other fbdev drivers. We fix this
by checking whether 'pixclock' is zero.

Similar commit: commit 16844e58704 ("video: fbdev: tridentfb:
Error out if 'pixclock' equals zero")

Signed-off-by: Alex Guo <redacted>
---
 drivers/video/fbdev/i740fb.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/video/fbdev/i740fb.c b/drivers/video/fbdev/i740fb.c
index 9b74dae71472..861e9e397b4e 100644
--- a/drivers/video/fbdev/i740fb.c
+++ b/drivers/video/fbdev/i740fb.c

@@ -419,6 +419,10 @@ static int i740fb_decode_var(const struct fb_var_screeninfo *var,
 
 
 	bpp = var->bits_per_pixel;
+	if (!var->pixclock){
+		dev_err(info->device, "pixclock must not be zero\n");
+		return -EINVAL;
+	}
 	switch (bpp) {
 	case 1 ... 8:
 		bpp = 8;

-- 
2.34.1

On Sat, 14 Jun 2025 01:18:37 -0400
Alex Guo [off-list ref] wrote:

Variable var->pixclock can be set by user. In case it equals to
zero, divide by zero would occur in 4 switch branches in
i740fb_decode_var.
Similar crashes have happened in other fbdev drivers. We fix this
by checking whether 'pixclock' is zero.

Doesn't it already hit the 'default' clause of the switch statement?

	David