linux-kernel - Re: [RFC PATCH v14 05/10] fs,landlock: Support filesystem access-control

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Message-ID: <CAG48ez1ETFhAZE1A9x=zB=b+t=pFYp3Yc0j8psFQhGwFRdDu2A@mail.gmail.com>
Date:   Thu, 27 Feb 2020 17:51:51 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Mickaël Salaün <mic@...ikod.net>
Cc:     kernel list <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...capital.net>,
        Arnd Bergmann <arnd@...db.de>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        James Morris <jmorris@...ei.org>, Jann Horn <jann@...jh.net>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Mickaël Salaün <mickael.salaun@....gouv.fr>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Shuah Khan <shuah@...nel.org>,
        Vincent Dagonneau <vincent.dagonneau@....gouv.fr>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux API <linux-api@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-doc@...r.kernel.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [RFC PATCH v14 05/10] fs,landlock: Support filesystem access-control

On Thu, Feb 27, 2020 at 5:50 PM Mickaël Salaün <mic@...ikod.net> wrote:
> On 26/02/2020 21:29, Jann Horn wrote:
> > On Mon, Feb 24, 2020 at 5:03 PM Mickaël Salaün <mic@...ikod.net> wrote:
> >> +static inline u32 get_mem_access(unsigned long prot, bool private)
> >> +{
> >> +       u32 access = LANDLOCK_ACCESS_FS_MAP;
> >> +
> >> +       /* Private mapping do not write to files. */
> >> +       if (!private && (prot & PROT_WRITE))
> >> +               access |= LANDLOCK_ACCESS_FS_WRITE;
> >> +       if (prot & PROT_READ)
> >> +               access |= LANDLOCK_ACCESS_FS_READ;
> >> +       if (prot & PROT_EXEC)
> >> +               access |= LANDLOCK_ACCESS_FS_EXECUTE;
> >> +       return access;
> >> +}
[...]
> However, I'm not sure this hook is useful for now. Indeed, the process
> still need to have a file descriptor open with the right accesses.

Yeah, agreed.