linux-kernel - Re: [PATCH] fs: create and use seq_show

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Date:	Sat, 8 Aug 2015 12:31:00 -0700
From:	Kees Cook <keescook@...omium.org>
To:	"J. R. Okajima" <hooanon05g@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Yan, Zheng" <zyan@...hat.com>, Sage Weil <sage@...hat.com>,
	Ilya Dryomov <idryomov@...il.com>,
	Steve French <sfrench@...ba.org>, Jan Kara <jack@...e.com>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	"Theodore Ts'o" <tytso@....edu>,
	Steven Whitehouse <swhiteho@...hat.com>,
	Bob Peterson <rpeterso@...hat.com>,
	Jeff Dike <jdike@...toit.com>,
	Richard Weinberger <richard@....at>,
	Mark Fasheh <mfasheh@...e.com>,
	Joel Becker <jlbec@...lplan.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	Dave Chinner <david@...morbit.com>, xfs@....sgi.com,
	Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"David S. Miller" <davem@...emloft.net>,
	Paul Moore <paul@...l-moore.com>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Eric Paris <eparis@...isplace.org>,
	James Morris <james.l.morris@...cle.com>,
	"Serge E. Hallyn" <serge@...lyn.com>, Jens Axboe <axboe@...com>,
	Fabian Frederick <fabf@...net.be>,
	Christoph Hellwig <hch@....de>, Firo Yang <firogm@...il.com>,
	David Howells <dhowells@...hat.com>,
	Jiri Slaby <jslaby@...e.cz>, Al Viro <viro@...iv.linux.org.uk>,
	Joe Perches <joe@...ches.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs: create and use seq_show_option for escaping

On Sat, Aug 8, 2015 at 9:41 AM, J. R. Okajima <hooanon05g@...il.com> wrote:
>
> Kees Cook:
>> This fixes the problem by adding new seq_show_option and seq_show_option_n
>> helpers, and updating the vulnerable show_option handlers to use them as
>> needed. Some, like SELinux, need to be open coded due to unusual existing
>> escape mechanisms.
>
> How about other ctrl chars such as CR or FF?
> I am using the similar function for many years, and it might be more
> generic because it supports all cntrl chars other than "\t\n\\" (see
> below).
>
> Many of other ctrl chars may not be necessary. But some people uses
> non-ASCII chars for their pathnames which may contain ESC or other
> chars. Any crazy chars can corrupt the output of /proc/mount and
> others. So it might be better to consider all ctrl chars.

While that's generally true, it's the consumers of mounts and
mountinfo that we need to worry about, and for those, it's only the
delimiters that we need to be concerned about (space, tab, newline,
and escapes).

However, since these consumers are expecting to deal with escapes, we
could, at any time, add new classes of characters to be escaped.

For this change, though, I wanted to keep it minimal for easiest backporting.

-Kees

-- 
Kees Cook
Chrome OS Security
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