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From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Daniel Vetter <daniel.vetter@ffwll.ch>,
	Geert Uytterhoeven <geert@linux-m68k.org>
Cc: 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,
	Randy Dunlap <rdunlap@infradead.org>
Subject: [PATCH] fbmem: don't allow too huge resolutions
Date: Tue, 31 Aug 2021 01:05:05 +0900	[thread overview]
Message-ID: <535e404d-03bf-8e7a-b296-132a2a98c599@i-love.sakura.ne.jp> (raw)
In-Reply-To: <339bfb21-8e80-c7d9-46dd-c416f87c50c0@infradead.org>

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.

This patch does not use array_size(), for array_size() is allowed to
return UINT_MAX on 32bits even if overflow did not happen. We want to
detect only overflow here, for individual module will recheck with more
strict limits as needed.

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>
Tested-by: syzbot <syzbot+04168c8063cfdde1db5e@syzkaller.appspotmail.com>
---
 drivers/video/fbdev/core/fbmem.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 1c855145711b..9f5075dc2345 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 > UINT_MAX ||
+	    (u64) var->xres_virtual * var->yres_virtual > UINT_MAX)
+		return -EINVAL;
+
 	ret = info->fbops->fb_check_var(var, info);
 
 	if (ret)
-- 
2.18.4



  reply	other threads:[~2021-08-30 16:05 UTC|newest]

Thread overview: 38+ 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
2021-07-14  5:16 ` syzbot
2021-08-30  0:24 ` Randy Dunlap
2021-08-30  2:27   ` Tetsuo Handa
2021-08-30  2:31     ` Randy Dunlap
2021-08-30 16:05       ` Tetsuo Handa [this message]
2021-08-31  6:48         ` [PATCH] fbmem: don't allow too huge resolutions Geert Uytterhoeven
2021-08-31  6:48           ` Geert Uytterhoeven
2021-08-31 15:23           ` Tetsuo Handa
2021-08-31 16:20             ` Daniel Vetter
2021-08-31 16:20               ` Daniel Vetter
2021-08-31 17:19             ` Geert Uytterhoeven
2021-08-31 17:19               ` Geert Uytterhoeven
2021-08-31 18:53               ` Daniel Vetter
2021-08-31 18:53                 ` Daniel Vetter
2021-08-31 18:56                 ` Geert Uytterhoeven
2021-08-31 18:56                   ` Geert Uytterhoeven
2021-08-31 19:04                   ` Daniel Vetter
2021-08-31 19:04                     ` Daniel Vetter
2021-09-01  1:14                     ` [PATCH v2] " Tetsuo Handa
2021-09-01  7:12                       ` Geert Uytterhoeven
2021-09-01  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 12:00       ` 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 14:30                 ` Geert Uytterhoeven
2021-08-30 14:38                 ` Tetsuo Handa
2021-08-30 14:53                   ` Geert Uytterhoeven
2021-08-30 14:53                     ` Geert Uytterhoeven
2021-08-30 15:00                     ` Geert Uytterhoeven
2021-08-30 15:00                       ` Geert Uytterhoeven

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