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

J. Bruce Fields
2019-06-26T16:21:51Z

On Mon, Jun 24, 2019 at 05:05:12PM -0400, J. Bruce Fields wrote:
> On Sat, Jun 22, 2019 at 01:22:56PM -0700, Kees Cook wrote:
> > On Sat, Jun 22, 2019 at 03:00:58PM -0400, J. Bruce Fields wrote:
> > > The logic around ESCAPE_NP and the "only" string is really confusing. I
> > > started assuming I could just add an ESCAPE_NONASCII flag and stick "
> > > and \ into the "only" string, but it doesn't work that way.
> >
> > Yeah, if ESCAPE_NP isn't specified, the "only" characters are passed
> > through. It'd be nice to have an "add" or a clearer way to do actual
> > ctype subsets, etc. If there isn't an obviously clear way to refactor
> > it, just skip it for now and I'm happy to ack your original patch. :)
>
> There may well be some simplification possible here.... There aren't
> really many users of "only", for example. I'll look into it some more.

The printk users are kind of mysterious to me. I did a grep for

git grep '%[0-9.*]pE'

which got 75 hits. All of them for pE. I couldn't find any of the
other pE[achnops] variants. pE is equivalent to ESCAPE_ANY|ESCAPE_NP.
Confusingly, ESCAPE_NP doesn't mean "escape non-printable", it means
"don't escape printable". So things like carriage returns aren't
escaped.

Of those 57 were in drivers/net/wireless, and from a quick check seemed
mostly to be for SSIDs in debug messages. I *think* SSIDs can be
arbitrary bytes? If they really want them escaped then I suspect they
want more than just nonprintable characters escaped.

One of the hits outside wireless code was in drm_dp_cec_adap_status,
which was printing some device ID into a debugfs file with "ID: %*pE\n".
If the ID actually needs escaping, then I suspect the meant to escape \n
too to prevent misparsing that output.

--b.