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From:   Kees Cook <keescook@chromium.org>
Date:   Fri, 9 Mar 2018 10:54:10 -0800
Message-ID: <CAGXu5j+-M1zWUrA8uX1=f46t2RAym6N-T_Sf8T0P1wFCMhNCAQ@mail.gmail.com>
Subject: Re: [PATCH net-next] modules: allow modprobe load regular elf binaries
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     David Miller <davem@davemloft.net>,
        Alexei Starovoitov <ast@fb.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Alexei Starovoitov <ast@kernel.org>,
        Djalal Harouni <tixxdz@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Greg KH <gregkh@linuxfoundation.org>,
        "Luis R. Rodriguez" <mcgrof@kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        kernel-team <kernel-team@fb.com>,
        Linux API <linux-api@vger.kernel.org>
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On Fri, Mar 9, 2018 at 10:50 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Fri, Mar 9, 2018 at 10:43 AM, Kees Cook <keescook@chromium.org> wrote:
>>
>> Module loading (via kernel_read_file()) already uses
>> deny_write_access(), and so does do_open_execat(). As long as module
>> loading doesn't call allow_write_access() before the execve() has
>> started in the new implementation, I think we'd be covered here.
>
> No. kernel_read_file() only does it *during* the read.

Ah, true. And looking at this again, shouldn't deny_write_access()
happen _before_ the LSM check in kernel_read_file()? That looks like a
problem...

-Kees

-- 
Kees Cook
Pixel Security