linux-kernel - Re: [PATCH] virt: vbox: Only copy_from

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Message-ID: <4f440336-608a-33a8-108a-8c53665a103a@redhat.com>
Date:   Tue, 8 May 2018 16:52:50 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virt: vbox: Only copy_from_user the request-header once

Hi,

On 08-05-18 16:21, Greg Kroah-Hartman wrote:
> On Tue, May 08, 2018 at 03:46:59PM +0200, Hans de Goede wrote:
>> In vbg_misc_device_ioctl(), the header of the ioctl argument is copied from
>> the userspace pointer 'arg' and saved to the kernel object 'hdr'. Then the
>> 'version', 'size_in', and 'size_out' fields of 'hdr' are verified.
>>
>> Before this commit, after the checks a buffer for the entire request would
>> be allocated and then all data including the verified header would be
>> copied from the userspace 'arg' pointer again.
>>
>> Given that the 'arg' pointer resides in userspace, a malicious userspace
>> process can race to change the data pointed to by 'arg' between the two
>> copies. By doing so, the user can bypass the verifications on the ioctl
>> argument.
>>
>> This commit fixes this by using the already checked copy of the header
>> to fill the header part of the allocated buffer and only copying the
>> remainder of the data from userspace.
>>
>> Reported-by: Wenwen Wang <wang6495@....edu>
>> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
> 
> Does this need to go into 4.17-final?  Any older kernels?  Or can it
> wait for 4.18-rc1?

I believe this can wait for 4.18-rc1.

Regards,

Hans