linux-kernel - Re: [RFC PATCH v2] fs/xattr: add *at family syscalls

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Message-ID: <CAMuHMdVa69s3g0z6qgayzNx=jT6Ko2RNeZehru0SbzYH8VwkfQ@mail.gmail.com>
Date:   Thu, 11 May 2023 17:17:29 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Christian Göttsche <cgzones@...glemail.com>
Cc:     x86@...nel.org, linux-alpha@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-ia64@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, audit@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        Nhat Pham <nphamcs@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH v2] fs/xattr: add *at family syscalls

Hi Christian,

On Thu, May 11, 2023 at 5:10 PM Christian Göttsche
<cgzones@...glemail.com> wrote:
> Add the four syscalls setxattrat(), getxattrat(), listxattrat() and
> removexattrat().  Those can be used to operate on extended attributes,
> especially security related ones, either relative to a pinned directory
> or on a file descriptor without read access, avoiding a
> /proc/<pid>/fd/<fd> detour, requiring a mounted procfs.
>
> One use case will be setfiles(8) setting SELinux file contexts
> ("security.selinux") without race conditions.
>
> Add XATTR flags to the private namespace of AT_* flags.
>
> Use the do_{name}at() pattern from fs/open.c.
>
> Use a single flag parameter for extended attribute flags (currently
> XATTR_CREATE and XATTR_REPLACE) and *at() flags to not exceed six
> syscall arguments in setxattrat().
>
> Previous approach ("f*xattr: allow O_PATH descriptors"): https://lore.kernel.org/all/20220607153139.35588-1-cgzones@googlemail.com/
> v1 discussion: https://lore.kernel.org/all/20220830152858.14866-2-cgzones@googlemail.com/
>
> Signed-off-by: Christian Göttsche <cgzones@...glemail.com>

Thanks for your patch!

The syscall numbers conflict with those used in "[PATCH] cachestat:
wire up cachestat for other architectures", so this needs some
synchronization.
https://lore.kernel.org/linux-sh/20230510195806.2902878-1-nphamcs@gmail.com

>  arch/m68k/kernel/syscalls/syscall.tbl       |   4 +

For m68k:
Acked-by: Geert Uytterhoeven <geert@...ux-m68k.org>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds