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

Tong Zhang
2022-02-09T07:55:24Z

On Tue, Feb 8, 2022 at 11:49 PM Domenico Andreoli
<domenico.andreoli@linux.com> 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@linux.com>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Amir Goldstein <amir73il@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Cc: Antti Palosaari <crope@iki.fi>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Benjamin LaHaise <bcrl@kvack.org>
> Cc: Clemens Ladisch <clemens@ladisch.de>
> Cc: David Airlie <airlied@linux.ie>
> Cc: Douglas Gilbert <dgilbert@interlog.com>
> Cc: Eric Biederman <ebiederm@xmission.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Iurii Zaikin <yzaikin@google.com>
> Cc: James E.J. Bottomley <jejb@linux.ibm.com>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Joel Becker <jlbec@evilplan.org>
> Cc: John Ogness <john.ogness@linutronix.de>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
> Cc: Julia Lawall <julia.lawall@inria.fr>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Lukas Middendorf <kernel@tuxforce.de>
> Cc: Mark Fasheh <mark@fasheh.com>
> Cc: Martin K. Petersen <martin.petersen@oracle.com>
> Cc: Paul Turner <pjt@google.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Petr Mladek <pmladek@suse.com>
> Cc: Phillip Potter <phil@philpotter.co.uk>
> Cc: Qing Wang <wangqing@vivo.com>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Sebastian Reichel <sre@kernel.org>
> Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
> Cc: Stephen Kitt <steve@sk2.org>
> Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
> Cc: Suren Baghdasaryan <surenb@google.com>
> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: "Theodore Ts'o" <tytso@mit.edu>
> Cc: Xiaoming Ni <nixiaoming@huawei.com>
>
> ---
> 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@gmail.com>