From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Randy Dunlap <rdunlap@infradead.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
syzbot <syzbot+04168c8063cfdde1db5e@syzkaller.appspotmail.com>,
akpm@linux-foundation.org, b.zolnierkie@samsung.com,
colin.king@canonical.com, dri-devel@lists.freedesktop.org,
linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org,
masahiroy@kernel.org, syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] BUG: unable to handle kernel paging request in vga16fb_fillrect
Date: Mon, 30 Aug 2021 11:27:27 +0900 [thread overview]
Message-ID: <2fccb5d3-191c-924e-159f-1c9d423e282f@i-love.sakura.ne.jp> (raw)
In-Reply-To: <131b24e5-ee31-6f7b-42b4-c34583711913@infradead.org>
On 2021/08/30 9:24, Randy Dunlap wrote:
> Note that yres_virtual is set to 0x10000000. Is there no practical limit
> (hence limit check) that can be used here?
>
> Also, in vga16fb_check_var(), beginning at line 404:
>
> 404 if (yres > vyres)
> 405 vyres = yres;
> 406 if (vxres * vyres > maxmem) {
> 407 vyres = maxmem / vxres;
> 408 if (vyres < yres)
> 409 return -ENOMEM;
> 410 }
>
> At line 406, the product of vxres * vyres overflows 32 bits (is 0 in this
> case/example), so any protection from this block is lost.
OK. Then, we can check overflow like below.
diff --git a/drivers/video/fbdev/vga16fb.c b/drivers/video/fbdev/vga16fb.c
index e2757ff1c23d..e483a3f5fd47 100644
--- a/drivers/video/fbdev/vga16fb.c
+++ b/drivers/video/fbdev/vga16fb.c
@@ -403,7 +403,7 @@ static int vga16fb_check_var(struct fb_var_screeninfo *var,
if (yres > vyres)
vyres = yres;
- if (vxres * vyres > maxmem) {
+ if ((u64) vxres * vyres > (u64) maxmem) {
vyres = maxmem / vxres;
if (vyres < yres)
return -ENOMEM;
But I think we can check overflow in the common code like below. (Both patch fixed the oops.)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 1c855145711b..8899679bbc46 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 > (u64) UINT_MAX ||
+ (u64) var->xres_virtual * var->yres_virtual > (u64) UINT_MAX)
+ return -EINVAL;
+
ret = info->fbops->fb_check_var(var, info);
if (ret)
>
> But even if yres_virtual (aka vyres) is "only" 0x01000000, so no
> multiplication overflow occurs, the resulting value of vyres "seems"
> to still be too large and can cause an error [I'm not sure about this
> last part -- I need to use a new gcc so that KASAN will work.]
next prev parent reply other threads:[~2021-08-30 2:28 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-14 5:16 [syzbot] BUG: unable to handle kernel paging request in vga16fb_fillrect syzbot
2021-08-30 0:24 ` Randy Dunlap
2021-08-30 2:27 ` Tetsuo Handa [this message]
2021-08-30 2:31 ` Randy Dunlap
2021-08-30 16:05 ` [PATCH] fbmem: don't allow too huge resolutions Tetsuo Handa
2021-08-31 6:48 ` Geert Uytterhoeven
2021-08-31 15:23 ` Tetsuo Handa
2021-08-31 16:20 ` Daniel Vetter
2021-08-31 17:19 ` Geert Uytterhoeven
2021-08-31 18:53 ` Daniel Vetter
2021-08-31 18:56 ` Geert Uytterhoeven
2021-08-31 19:04 ` Daniel Vetter
2021-09-01 1:14 ` [PATCH v2] " Tetsuo Handa
2021-09-01 7:12 ` Geert Uytterhoeven
2021-09-08 10:27 ` [PATCH v2 (repost)] " Tetsuo Handa
2021-09-08 16:52 ` Daniel Vetter
2021-08-30 12:00 ` [syzbot] BUG: unable to handle kernel paging request in vga16fb_fillrect Geert Uytterhoeven
2021-08-30 13:00 ` Dan Carpenter
2021-08-30 13:37 ` Tetsuo Handa
2021-08-30 13:47 ` Dan Carpenter
2021-08-30 14:25 ` Tetsuo Handa
2021-08-30 14:29 ` Dan Carpenter
2021-08-30 14:30 ` Geert Uytterhoeven
2021-08-30 14:38 ` Tetsuo Handa
2021-08-30 14:53 ` Geert Uytterhoeven
2021-08-30 15:00 ` Geert Uytterhoeven
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