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fbmem: don't allow too huge resolutions

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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
This commit is contained in:
Tetsuo Handa 2021-09-08 19:27:49 +09:00 committed by Daniel Vetter
parent 87fd9ef475
commit 8c28051cdc
1 changed files with 6 additions and 0 deletions
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6
drivers/video/fbdev/core/fbmem.c
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@ -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)