Re: [PATCH 08/16] nfsd: escape high characters in binary data

Kees Cook
2019-06-21T22:26:05Z

On Fri, Jun 21, 2019 at 01:45:44PM -0400, J. Bruce Fields wrote:
> I'm not sure who to get review from for this kind of thing.
>
> Kees, you seem to be one of the only people to touch string_helpers.c
> at all recently, any ideas?

Hi! Yeah, I'm happy to take a look. Notes below...

>
> --b.
>
> On Thu, Jun 20, 2019 at 10:51:07AM -0400, J. Bruce Fields wrote:
> > From: "J. Bruce Fields" <bfields@redhat.com>
> >
> > I'm exposing some information about NFS clients in pseudofiles. I
> > expect to eventually have simple tools to help read those pseudofiles.
> >
> > But it's also helpful if the raw files are human-readable to the extent
> > possible. It aids debugging and makes them usable on systems that don't
> > have the latest nfs-utils.
> >
> > A minor challenge there is opaque client-generated protocol objects like
> > state owners and client identifiers. Some clients generate those to
> > include handy information in plain ascii. But they may also include
> > arbitrary byte sequences.
> >
> > I think the simplest approach is to limit to isprint(c) && isascii(c)
> > and escape everything else.

Can you get the same functionality out of sprintf's %pE (escaped
string)? If not, maybe we should expand the flags available?

* - 'E[achnops]' For an escaped buffer, where rules are defined by
* combination
* of the following flags (see string_escape_mem() for
* the
* details):
* a - ESCAPE_ANY
* c - ESCAPE_SPECIAL
* h - ESCAPE_HEX
* n - ESCAPE_NULL
* o - ESCAPE_OCTAL
* p - ESCAPE_NP
* s - ESCAPE_SPACE
* By default ESCAPE_ANY_NP is used.

This doesn't cover escaping >0x7f and " and \

And perhaps I should rework kstrdup_quotable() to have that flag? It's
not currently escaping non-ascii and it probably should. Maybe
"ESCAPE_QUOTABLE" as "q"?

--
Kees Cook