linux-kernel - Re: [PATCH] linux/nospec.h: allow index argument to have const-qualified type

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 15 Feb 2018 14:03:51 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>,
        Ingo Molnar <mingo@...nel.org>,
        stable <stable@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] linux/nospec.h: allow index argument to have
 const-qualified type

On Thu, Feb 15, 2018 at 1:56 PM, Dan Williams <dan.j.williams@...el.com> wrote:
>
> So I don't mind removing it, but I don't think it is garbage. It's
> there purely as a notification to the odd kernel developer that wants
> to pass "insane" index values,

But the thing is, the "index" value isn't even kernel-supplied.

Here's a test:  run a 32-bit kernel, and then do an ioctl() or
something with a negative fd.

What I think will happen is:

 - the negative fd will be seen as a big 'unsigned int' here:

        fcheck_files(struct files_struct *files, unsigned int fd)

which then does

                fd = array_index_nospec(fd, fdt->max_fds);

and that existing *STUPID* and *WRONG* WARN_ON() will trigger.

Sure, you can't trigger it on 64-bit kernels because there the
"unsigned int" will be small compared to LONG_MAX, but..

It is simply is *wrong* to check the "index".  It really fundamentally
is complete garbage.

Because the whole - and ONLY - *point* of this is that you have an
untrusted index. So checking it and giving a warning when it's out of
range is pure garbage.

Really. That warning must go away. Stop arguing for it, it's stupid and wrong.

Checking _size_ is one thing, but honestly, that's questionable too.

                  Linus