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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Alexey Gladkov <gladkov.alexey@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        Linux API <linux-api@vger.kernel.org>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        Linux Security Module <linux-security-module@vger.kernel.org>,
        Akinobu Mita <akinobu.mita@gmail.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Daniel Micay <danielmicay@gmail.com>,
        Djalal Harouni <tixxdz@gmail.com>,
        "Dmitry V . Levin" <ldv@altlinux.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        "J . Bruce Fields" <bfields@fieldses.org>,
        Jeff Layton <jlayton@poochiereds.net>,
        Jonathan Corbet <corbet@lwn.net>,
        Kees Cook <keescook@chromium.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        David Howells <dhowells@redhat.com>
References: <20200327172331.418878-1-gladkov.alexey@gmail.com>
        <20200327172331.418878-9-gladkov.alexey@gmail.com>
        <87d08pkh4u.fsf@x220.int.ebiederm.org>
        <20200402165156.4mzenof4upvtd3lv@comp-core-i7-2640m-0182e6>
Date:   Thu, 02 Apr 2020 12:04:44 -0500
In-Reply-To: <20200402165156.4mzenof4upvtd3lv@comp-core-i7-2640m-0182e6>
        (Alexey Gladkov's message of "Thu, 2 Apr 2020 18:51:56 +0200")
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Subject: Re: [PATCH v10 8/9] proc: use human-readable values for hidehid
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Alexey Gladkov <gladkov.alexey@gmail.com> writes:

> On Thu, Apr 02, 2020 at 11:05:21AM -0500, Eric W. Biederman wrote:
>> Alexey Gladkov <gladkov.alexey@gmail.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