Re: [PATCH v2] Fix regression due to "fs: move binfmt_misc sysctl to its own file"

[Tong Zhang]

On Tue, Feb 8, 2022 at 11:49 PM Domenico Andreoli
<domenico.andreoli@xxxxxxxxx> wrote:
>
> Commit 3ba442d5331f did not go unnoticed, binfmt-support stopped to
> work on my Debian system since v5.17-rc2 (did not check with -rc1).
>
> The existance of the /proc/sys/fs/binfmt_misc is a precondition for
> attempting to mount the binfmt_misc fs, which in turn triggers the
> autoload of the binfmt_misc module. Without it, no module is loaded
> and no binfmt is available at boot.
>
> Building as built-in or manually loading the module and mounting the fs
> works fine, it's therefore only a matter of interaction with user-space.
> I could try to improve the Debian systemd configuration but I can't
> say anything about the other distributions.
>
> This patch restores a working system right after boot.
>
> v2:
> - move creation of fs/binfmt_misc to fs/file_table.c
> - use IS_ENABLED() to conditionally create it
>
> Fixes: 3ba442d5331f ("fs: move binfmt_misc sysctl to its own file")
> Signed-off-by: Domenico Andreoli <domenico.andreoli@xxxxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Amir Goldstein <amir73il@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Cc: Antti Palosaari <crope@xxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> Cc: Benjamin LaHaise <bcrl@xxxxxxxxx>
> Cc: Clemens Ladisch <clemens@xxxxxxxxxx>
> Cc: David Airlie <airlied@xxxxxxxx>
> Cc: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
> Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Iurii Zaikin <yzaikin@xxxxxxxxxx>
> Cc: James E.J. Bottomley <jejb@xxxxxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> Cc: Joel Becker <jlbec@xxxxxxxxxxxx>
> Cc: John Ogness <john.ogness@xxxxxxxxxxxxx>
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> Cc: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx>
> Cc: Julia Lawall <julia.lawall@xxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Lukas Middendorf <kernel@xxxxxxxxxxx>
> Cc: Mark Fasheh <mark@xxxxxxxxxx>
> Cc: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
> Cc: Paul Turner <pjt@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Petr Mladek <pmladek@xxxxxxxx>
> Cc: Phillip Potter <phil@xxxxxxxxxxxxxxxx>
> Cc: Qing Wang <wangqing@xxxxxxxx>
> Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> Cc: Sebastian Reichel <sre@xxxxxxxxxx>
> Cc: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
> Cc: Stephen Kitt <steve@xxxxxxx>
> Cc: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: "Theodore Ts'o" <tytso@xxxxxxx>
> Cc: Xiaoming Ni <nixiaoming@xxxxxxxxxx>
>
> ---
>  fs/binfmt_misc.c |    6 +-----
>  fs/file_table.c  |    2 ++
>  2 files changed, 3 insertions(+), 5 deletions(-)
>
> Index: b/fs/binfmt_misc.c
> ===================================================================
> --- a/fs/binfmt_misc.c
> +++ b/fs/binfmt_misc.c
> @@ -817,20 +817,16 @@ static struct file_system_type bm_fs_typ
>  };
>  MODULE_ALIAS_FS("binfmt_misc");
>
> -static struct ctl_table_header *binfmt_misc_header;
> -
>  static int __init init_misc_binfmt(void)
>  {
>         int err = register_filesystem(&bm_fs_type);
>         if (!err)
>                 insert_binfmt(&misc_format);
> -       binfmt_misc_header = register_sysctl_mount_point("fs/binfmt_misc");
> -       return 0;
> +       return err;
>  }
>
>  static void __exit exit_misc_binfmt(void)
>  {
> -       unregister_sysctl_table(binfmt_misc_header);
>         unregister_binfmt(&misc_format);
>         unregister_filesystem(&bm_fs_type);
>  }
> Index: b/fs/file_table.c
> ===================================================================
> --- a/fs/file_table.c
> +++ b/fs/file_table.c
> @@ -119,6 +119,8 @@ static struct ctl_table fs_stat_sysctls[
>  static int __init init_fs_stat_sysctls(void)
>  {
>         register_sysctl_init("fs", fs_stat_sysctls);
> +       if (IS_ENABLED(CONFIG_BINFMT_MISC))
> +               register_sysctl_mount_point("fs/binfmt_misc");
>         return 0;
>  }
>  fs_initcall(init_fs_stat_sysctls);

Looks good
Thanks!

Reviewed-by: Tong Zhang <ztong0001@xxxxxxxxx>