syzbot is reporting page fault at vga16fb_fillrect() [1], for
vga16fb_check_var() is failing to detect multiplication overflow.
if (vxres * vyres > maxmem) {
vyres = maxmem / vxres;
if (vyres < yres)
return -ENOMEM;
}
Since no module would accept too huge resolutions where multiplication
overflow happens, let's reject in the common path.
This patch does not use array_size(), for array_size() is allowed to
return UINT_MAX on 32bits even if overflow did not happen. We want to
detect only overflow here, for individual module will recheck with more
strict limits as needed.
Link: https://syzkaller.appspot.com/bug?extid=04168c8063cfdde1db5e [1]
Reported-by: syzbot <syzbot+04168c8063cfdde1db5e@xxxxxxxxxxxxxxxxxxxxxxxxx>
Debugged-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Tested-by: syzbot <syzbot+04168c8063cfdde1db5e@xxxxxxxxxxxxxxxxxxxxxxxxx>
---
drivers/video/fbdev/core/fbmem.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 1c855145711b..9f5075dc2345 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1008,6 +1008,11 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
if (var->xres < 8 || var->yres < 8)
return -EINVAL;
+ /* Don't allow u32 * u32 to overflow. */
+ if ((u64) var->xres * var->yres > UINT_MAX ||
+ (u64) var->xres_virtual * var->yres_virtual > UINT_MAX)
+ return -EINVAL;
+
ret = info->fbops->fb_check_var(var, info);
if (ret)
--
2.18.4
