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

[harperchen <harperchen1110@gmail.com>]

fb_set_var would by called when user invokes ioctl with cmd
FBIOPUT_VSCREENINFO. User-provided data would finally reach
tgafb_check_var. In case var->pixclock is assigned to zero,
divide by zero would occur when checking whether reciprocal
of var->pixclock is too high.

Similar crashes have happened in other fbdev drivers. There
is no check and modification on var->pixclock along the call
chain to tgafb_check_var. We believe it could also be triggered
in driver tgafb from user site.

Signed-off-by: harperchen <harperchen1110@gmail.com>
---
 drivers/video/fbdev/tgafb.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/video/fbdev/tgafb.c b/drivers/video/fbdev/tgafb.c
index 14d37c49633c..b44004880f0d 100644
--- a/drivers/video/fbdev/tgafb.c
+++ b/drivers/video/fbdev/tgafb.c
@@ -173,6 +173,9 @@ tgafb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
 {
 	struct tga_par *par = (struct tga_par *)info->par;
 
+	if (!var->pixclock)
+		return -EINVAL;
+
 	if (par->tga_type == TGA_TYPE_8PLANE) {
 		if (var->bits_per_pixel != 8)
 			return -EINVAL;
-- 
2.25.1