linux-kernel - Re: [PATCH v10 8/9] proc: use human-readable values for hidehid

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Message-ID: <87d08pkh4u.fsf@x220.int.ebiederm.org>
Date:   Thu, 02 Apr 2020 11:05:21 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Alexey Gladkov <gladkov.alexey@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux API <linux-api@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linux Security Module <linux-security-module@...r.kernel.org>,
        Akinobu Mita <akinobu.mita@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Alexey Gladkov <legion@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Daniel Micay <danielmicay@...il.com>,
        Djalal Harouni <tixxdz@...il.com>,
        "Dmitry V . Levin" <ldv@...linux.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Jeff Layton <jlayton@...chiereds.net>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        David Howells <dhowells@...hat.com>
Subject: Re: [PATCH v10 8/9] proc: use human-readable values for hidehid

Alexey Gladkov <gladkov.alexey@...il.com> writes:

> The hidepid parameter values are becoming more and more and it becomes
> difficult to remember what each new magic number means.

In principle I like this change.  In practice I think you have just
broken ABI compatiblity with the new mount ABI.

In particular the following line seems broken.

> diff --git a/fs/proc/root.c b/fs/proc/root.c
> index dbcd96f07c7a..ba782d6e6197 100644
> --- a/fs/proc/root.c
> +++ b/fs/proc/root.c
> @@ -45,7 +45,7 @@ enum proc_param {
>  
>  static const struct fs_parameter_spec proc_fs_parameters[] = {
>  	fsparam_u32("gid",	Opt_gid),
> -	fsparam_u32("hidepid",	Opt_hidepid),
> +	fsparam_string("hidepid",	Opt_hidepid),
>  	fsparam_string("subset",	Opt_subset),
>  	{}
>  };

As I read fs_parser.c fs_param_is_u32 handles string inputs and turns them
into numbers, and it handles binary numbers.  However fs_param_is_string
appears to only handle strings.  It appears to have not capacity to turn
raw binary numbers into strings.

So I think we probably need to fix fs_param_is_string to raw binary
numbers before we can safely make this change to fs/proc/root.c

David am I reading the fs_parser.c code correctly?  If I am are you ok
with a change like the above?

Eric