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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, George Kennedy <george.kennedy@oracle.com>,
        syzbot+e5fd3e65515b48c02a30@syzkaller.appspotmail.com,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Dhaval Giani <dhaval.giani@oracle.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Subject: [PATCH 4.14 20/23] fbmem: add margin check to fb_check_caps()
Date:   Wed,  1 Sep 2021 14:27:05 +0200
Message-Id: <20210901122250.435100302@linuxfoundation.org>
In-Reply-To: <20210901122249.786673285@linuxfoundation.org>
References: <20210901122249.786673285@linuxfoundation.org>
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From: George Kennedy <george.kennedy@oracle.com>

commit a49145acfb975d921464b84fe00279f99827d816 upstream.

A fb_ioctl() FBIOPUT_VSCREENINFO call with invalid xres setting
or yres setting in struct fb_var_screeninfo will result in a
KASAN: vmalloc-out-of-bounds failure in bitfill_aligned() as
the margins are being cleared. The margins are cleared in
chunks and if the xres setting or yres setting is a value of
zero upto the chunk size, the failure will occur.

Add a margin check to validate xres and yres settings.

Signed-off-by: George Kennedy <george.kennedy@oracle.com>
Reported-by: syzbot+e5fd3e65515b48c02a30@syzkaller.appspotmail.com
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Dhaval Giani <dhaval.giani@oracle.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1594149963-13801-1-git-send-email-george.kennedy@oracle.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/video/fbdev/core/fbmem.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1003,6 +1003,10 @@ fb_set_var(struct fb_info *info, struct
 			goto done;
 		}
 
+		/* bitfill_aligned() assumes that it's at least 8x8 */
+		if (var->xres < 8 || var->yres < 8)
+			return -EINVAL;
+
 		ret = info->fbops->fb_check_var(var, info);
 
 		if (ret)