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

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Date: Thu, 2 Apr 2020 18:51:56 +0200
From: Alexey Gladkov <gladkov.alexey@...il.com>
To: "Eric W. Biederman" <ebiederm@...ssion.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

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 ?

> 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
> 

-- 
Rgrds, legion

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