Commit 5de2ee62 authored Sep 08, 2021 by Tetsuo Handa Committed by Greg Kroah-Hartman Sep 15, 2021

fbmem: don't allow too huge resolutions

commit 8c28051cdcbe9dfcec6bd0a4709d67a09df6edae upstream.

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>
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/185175d6-227a-7b55-433d-b070929b262c@i-love.sakura.ne.jp


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 4a95b04a

drivers/video/fbdev/core/fbmem.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -957,6 +957,7 @@ 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;
		@@ -1003,6 +1004,11 @@ 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)