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From: Kees Cook <keescook@chromium.org>
To: "J. Bruce Fields" <bfields@fieldses.org>
Cc: linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>
Subject: Re: [PATCH 08/16] nfsd: escape high characters in binary data
Date: Wed, 26 Jun 2019 21:16:44 -0700
Message-ID: <201906262100.00C1C22@keescook> (raw)
In-Reply-To: <20190626162149.GB4144@fieldses.org>

On Wed, Jun 26, 2019 at 12:21:49PM -0400, J. Bruce Fields wrote:
> 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.

I saw pEn and pEhp and pEp:

drivers/staging/rtl8192e/rtllib.h:      snprintf(escaped, sizeof(escaped), "%*pEn", essid_len, essid);
drivers/staging/rtl8192u/ieee80211/ieee80211.h: snprintf(escaped, sizeof(escaped), "%*pEn", essid_len, essid);
drivers/staging/wlan-ng/prism2sta.c: netdev_info(wlandev->netdev, "Prism2 card SN: %*pEhp\n",
drivers/thunderbolt/xdomain.c:  return sprintf(buf, "%*pEp\n", (int)strlen(svc->key), svc->key);

However, every use was insufficient, AFAICT.

This:
	git grep -2 '\bescape_essid\b'
Shows that all the staging uses end up getting logged as: '%s' so their
escaping is insufficient.

> Confusingly, ESCAPE_NP doesn't mean "escape non-printable", it means
> "don't escape printable".  So things like carriage returns aren't
> escaped.

Right -- any they're almost all logged surrounded by ' or " which means
those would need to be escaped as well. The prism2 is leaking newlines
too, as well as the thunderbolt sysfs printing.

So... seems like we should fix this. :P

> 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.

I think we need to make the default produce "loggable" output.
non-ascii, non-printables, \, ', and " need to be escaped. Maybe " "
too?

-- 
Kees Cook

  reply index

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-20 14:50 [PATCH 00/16] exposing knfsd client state to userspace J. Bruce Fields
2019-06-20 14:51 ` [PATCH 01/16] nfsd: persist nfsd filesystem across mounts J. Bruce Fields
2019-06-20 14:51 ` [PATCH 02/16] nfsd: rename cl_refcount J. Bruce Fields
2019-06-20 14:51 ` [PATCH 03/16] nfsd4: use reference count to free client J. Bruce Fields
2019-06-20 14:51 ` [PATCH 04/16] nfsd: add nfsd/clients directory J. Bruce Fields
2019-06-20 14:51 ` [PATCH 05/16] nfsd: make client/ directory names small ints J. Bruce Fields
2019-06-20 14:51 ` [PATCH 06/16] nfsd4: add a client info file J. Bruce Fields
2019-06-20 14:51 ` [PATCH 07/16] nfsd: copy client's address including port number to cl_addr J. Bruce Fields
2019-06-20 14:51 ` [PATCH 08/16] nfsd: escape high characters in binary data J. Bruce Fields
2019-06-21 17:45   ` bfields
2019-06-21 22:26     ` Kees Cook
2019-06-22 19:00       ` J. Bruce Fields
2019-06-22 20:22         ` Kees Cook
2019-06-24 21:05           ` J. Bruce Fields
2019-06-26 16:21             ` J. Bruce Fields
2019-06-27  4:16               ` Kees Cook [this message]
2019-06-27 15:23                 ` J. Bruce Fields
2019-06-27 20:21               ` J. Bruce Fields
2019-06-28  3:58                 ` Kees Cook
2019-06-28 16:33                   ` J. Bruce Fields
2019-07-10 22:09                     ` J. Bruce Fields
2019-07-11  1:54                       ` Kees Cook
2019-08-06 12:19   ` Andy Shevchenko
2019-08-06 18:50     ` J. Bruce Fields
2019-08-07  9:00       ` Andy Shevchenko
2019-08-08 11:28         ` bfields
2019-08-27 13:36           ` Andy Shevchenko
2019-06-20 14:51 ` [PATCH 09/16] nfsd: add more information to client info file J. Bruce Fields
2019-06-20 14:51 ` [PATCH 10/16] nfsd4: add file to display list of client's opens J. Bruce Fields
2019-06-20 14:51 ` [PATCH 11/16] nfsd: show lock and deleg stateids J. Bruce Fields
2019-06-20 14:51 ` [PATCH 12/16] nfsd4: show layout stateids J. Bruce Fields
2019-06-20 14:51 ` [PATCH 13/16] nfsd: create get_nfsdfs_clp helper J. Bruce Fields
2019-06-20 14:51 ` [PATCH 14/16] nfsd: allow forced expiration of NFSv4 clients J. Bruce Fields
2019-06-20 14:51 ` [PATCH 15/16] nfsd: create xdr_netobj_dup helper J. Bruce Fields
2019-06-20 14:51 ` [PATCH 16/16] nfsd: decode implementation id J. Bruce Fields
2019-06-21 18:13 ` [PATCH 00/16] exposing knfsd client state to userspace bfields
2019-06-21 19:25   ` Anna Schumaker
2019-06-21 22:08     ` J. Bruce Fields

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