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

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Message-ID: <87r1x5iztf.fsf@x220.int.ebiederm.org>
Date:   Thu, 02 Apr 2020 12:04:44 -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>,
        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:

> On Thu, Apr 02, 2020 at 11:05:21AM -0500, Eric W. Biederman wrote:
>> 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.
>
> I use result only with hidepid_u32_spec and nobody modifies param->string.
> I do not use internal functions here.
>
> I don’t follow how a raw number can get here ?

I may be wrong but last I looked you can input raw numbers using the new
mount api.   I have most of the details paged out at the moment,
but I believe that is why when you set a parameter in the new mount api
it takes a type.

>> 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