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To:     linux-kernel@vger.kernel.org
From:   Tavis Ormandy <taviso@gmail.com>
Subject: Re: [PATCH 186/190] Revert "virt: vbox: Only copy_from_user the
 request-header once"
Date:   Wed, 21 Apr 2021 15:14:29 -0000 (UTC)
Message-ID: <s5pfgl$all$1@ciao.gmane.io>
References: <20210421130105.1226686-1-gregkh@linuxfoundation.org>
 <20210421130105.1226686-187-gregkh@linuxfoundation.org>
User-Agent: slrn/pre1.0.4-5 (Linux)
Precedence: bulk

On 2021-04-21, Greg Kroah-Hartman wrote:
> This reverts commit bd23a7269834dc7c1f93e83535d16ebc44b75eba.
>
> -	*((struct vbg_ioctl_hdr *)buf) = hdr;
> -	if (copy_from_user(buf + sizeof(hdr), (void *)arg + sizeof(hdr),
> -			   hdr.size_in - sizeof(hdr))) {
> +	if (copy_from_user(buf, (void *)arg, hdr.size_in)) {
>  		ret = -EFAULT;
>  		goto out;
>  	}

This one seems like a real bugfix, otherwise there's a double-fetch from
userspace, and a TOCTOU with the hdr fields that could cause a OOB read.

Reviewed-by: Tavis Ormandy <taviso@gmail.com>

Tavis.


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