On Wed, Sep 08, 2021 at 07:27:49PM +0900, Tetsuo Handa wrote:
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.
Link: https://syzkaller.appspot.com/bug?extid=04168c8063cfdde1db5e [1] Reported-by: syzbot syzbot+04168c8063cfdde1db5e@syzkaller.appspotmail.com Debugged-by: Randy Dunlap rdunlap@infradead.org Signed-off-by: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Reviewed-by: Geert Uytterhoeven geert+renesas@glider.be
Changes in v2: Use check_mul_overflow(), suggested by Geert Uytterhoeven geert@linux-m68k.org.
Pushed to drm-misc-next-fixes so it should get into current merge window.
I also added a cc: stable here, I htink it's needed.
Thanks a lot to both you&Geert for handling this! -Daniel
drivers/video/fbdev/core/fbmem.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 71fb710f1ce3..7420d2c16e47 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -962,6 +962,7 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var) struct fb_var_screeninfo old_var; struct fb_videomode mode; struct fb_event event;
u32 unused;
if (var->activate & FB_ACTIVATE_INV_MODE) { struct fb_videomode mode1, mode2;
@@ -1008,6 +1009,11 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var) if (var->xres < 8 || var->yres < 8) return -EINVAL;
/* Too huge resolution causes multiplication overflow. */
if (check_mul_overflow(var->xres, var->yres, &unused) ||
check_mul_overflow(var->xres_virtual, var->yres_virtual, &unused))return -EINVAL;ret = info->fbops->fb_check_var(var, info);
if (ret)
-- 2.18.4