diff mbox series

[v2] fbmem: don't allow too huge resolutions

Message ID 750ed1ae-de80-b232-4aea-79d60c212fab@i-love.sakura.ne.jp (mailing list archive)
State Superseded, archived
Headers show
Series [v2] fbmem: don't allow too huge resolutions | expand

Commit Message

Tetsuo Handa Sept. 1, 2021, 1:14 a.m. UTC
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>
---
Changes in v2:
  Use check_mul_overflow(), suggested by Geert Uytterhoeven <geert@linux-m68k.org>.

 drivers/video/fbdev/core/fbmem.c | 6 ++++++
 1 file changed, 6 insertions(+)

Comments

Geert Uytterhoeven Sept. 1, 2021, 7:12 a.m. UTC | #1
On Wed, Sep 1, 2021 at 3:15 AM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> 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>

Gr{oetje,eeting}s,

                        Geert
diff mbox series

Patch

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 1c855145711b..53d23b3d010c 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)