[PATCH AUTOSEL 5.4 6/6] fbmon: prevent division by zero in fb_videomode_from_videomode()

[Sasha Levin]

From: Roman Smirnov <r.smir...@omp.ru>

[ Upstream commit c2d953276b8b27459baed1277a4fdd5dd9bd4126 ]

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.smir...@omp.ru>
Reviewed-by: Sergey Shtylyov <s.shtyl...@omp.ru>
Signed-off-by: Helge Deller <del...@gmx.de>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
 drivers/video/fbdev/core/fbmon.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/video/fbdev/core/fbmon.c b/drivers/video/fbdev/core/fbmon.c
index 8e2e19f3bf441..dab5fdeafa97d 100644
--- a/drivers/video/fbdev/core/fbmon.c
+++ b/drivers/video/fbdev/core/fbmon.c
@@ -1311,7 +1311,7 @@ int fb_get_mode(int flags, u32 val, struct 
fb_var_screeninfo *var, struct fb_inf
 int fb_videomode_from_videomode(const struct videomode *vm,
                                struct fb_videomode *fbmode)
 {
-       unsigned int htotal, vtotal;
+       unsigned int htotal, vtotal, total;
 
        fbmode->xres = vm->hactive;
        fbmode->left_margin = vm->hback_porch;
@@ -1344,8 +1344,9 @@ 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) {
-               fbmode->refresh = vm->pixelclock / (htotal * vtotal);
+       total = htotal * vtotal;
+       if (total) {
+               fbmode->refresh = vm->pixelclock / total;
        /* a mode must have htotal and vtotal != 0 or it is invalid */
        } else {
                fbmode->refresh = 0;
-- 
2.43.0