linux-kernel - Re: [GIT PULL] Add trusted_for(2) (was O

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Date:   Wed, 8 Feb 2023 11:32:23 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Mickaël Salaün <mic@...ikod.net>
Cc:     concord@...too.org, linux-hardening@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Heimes <christian@...hon.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        James Morris <jmorris@...ei.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Muhammad Usama Anjum <usama.anjum@...labora.com>,
        Paul Moore <paul@...l-moore.com>,
        Philippe Trébuchet 
        <philippe.trebuchet@....gouv.fr>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Steve Dower <steve.dower@...hon.org>,
        Thibaut Sautereau <thibaut.sautereau@....gouv.fr>,
        Vincent Strubel <vincent.strubel@....gouv.fr>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Christian Brauner <brauner@...nel.org>,
        Theodore Ts'o <tytso@....edu>
Subject: Re: [GIT PULL] Add trusted_for(2) (was O_MAYEXEC)

*thread necromancy*

On Tue, Apr 05, 2022 at 06:09:03PM +0200, Mickaël Salaün wrote:
> 
> On 05/04/2022 01:26, Linus Torvalds wrote:
> > On Mon, Apr 4, 2022 at 3:25 PM Kees Cook <keescook@...omium.org> wrote:
> 
> [...]
> 
> > 
> > > I think this already exists as AT_EACCESS? It was added with
> > > faccessat2() itself, if I'm reading the history correctly.
> > 
> > Yeah, I noticed myself, I just hadn't looked (and I don't do enough
> > user-space programming to be aware of if that way).
> 
> I think AT_EACCESS should be usable with the new EXECVE_OK too.
> 
> 
> > 
> > > >      (a) "what about suid bits that user space cannot react to"
> > > 
> > > What do you mean here? Do you mean setid bits on the file itself?
> > 
> > Right.
> > 
> > Maybe we don't care.
> 
> I think we don't. I think the only corner case that could be different is
> for files that are executable, SUID and non-readable. In this case it
> wouldn't matter because userspace could not read the file, which is required
> for interpretation/execution. Anyway, S[GU]ID bits in scripts are just
> ignored by execve and we want to follow the same semantic.

Hi Mickaël,

Is there a new version of this being worked on? It would be really nice
to have the O_MAYEXEC/faccessat2() visibility for script execution control
in userspace. It seems like it would be mainly a respin of an earlier
version of this series before trusted_for() was proposed.

-Kees

-- 
Kees Cook