linux-kernel - Re: [PATCH v9] fs: clear file privilege bits when mmap writing

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Message-ID: <CAGXu5jLfsACfz7HqZH3p5_CanbrUQWBU8HtfgsruycmEKsO38A@mail.gmail.com>
Date:   Tue, 7 Feb 2017 12:18:50 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Konstantin Khlebnikov <koct9i@...il.com>,
        Jan Kara <jack@...e.cz>, yalin wang <yalin.wang2010@...il.com>,
        Willy Tarreau <w@....eu>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9] fs: clear file privilege bits when mmap writing

On Fri, Jan 27, 2017 at 7:47 PM, Andy Lutomirski <luto@...nel.org> wrote:
> On Wed, May 25, 2016 at 2:49 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
>> On Wed, May 25, 2016 at 02:36:57PM -0700, Kees Cook wrote:
>>
>>> Hm, this didn't end up getting picked up. (This jumped out at me again
>>> because i_mutex just vanished...)
>>>
>>> Al, what's the right way to update the locking in this patch?
>>
>> ->i_mutex is dealt with just by using lock_inode(inode)/unlock_inode(inode);
>> I hadn't looked at the rest of the locking in there.
>
> Ping?
>
> If this is too messy, I'm wondering if we could get away with a much
> simpler approach: clear the suid and sgid bits when the file is opened
> for write.

I think that'll break something, but I don't have any actual examples.
Regardless, I'd still like to see this hole fixed...

-Kees

-- 
Kees Cook
Pixel Security