dtprintinfo: Fix a potential exploitable buffer overrun

dtprintinfo: Fix a potential exploitable buffer overrun

This fixes a potentially exploitable buffer overrun in dtprintinfo.
This was brought to my attention based on a 0day exploit released for
Solaris CDE.

The exploit code does not work (or build) on linux, and the overrun is
in the heap rather than the stack as on Solaris, but it's easy to see
how this could be exploited.

The following is the content of the advisory:

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@Mediaservice.net (Cybaze Group) Security Advisory #2019-01 (2019-05-07)

         Title:	Local privilege escalation via CDE dtprintinfo
   Application:	Common Desktop Environment 2.3.0 and earlier
     Platforms:	Oracle Solaris 10 1/13 (Update 11) and earlier
   Description:	A local attacker can gain root privileges by exploiting
		a buffer overflow in CDE dtprintinfo
        Author:	Marco Ivaldi <marco.ivaldi@mediaservice.net>
   Contributor:	Dave Aitel <dave.aitel@cyxtera.com> (original discovery)
 Vendor Status:	<secalert_us@oracle.com> notified on 2019-05-05
		<cdesktopenv-devel@lists.sourceforge.net> notified on 2019-05-05
           CVE:	The Common Vulnerabilities and Exposures project has not assigned
		a name to this issue yet
    References: https://lab.mediaservice.net/advisory/2019-01-cde-dtprintinfo.txt
		https://github.com/0xdea/raptor_infiltrate19
		https://sourceforge.net/p/cdesktopenv/wiki/Home/
		https://www.oracle.com/technetwork/server-storage/solaris10/
		https://www.mediaservice.net/
		https://infiltratecon.com/

1. Abstract.

A buffer overflow in the DtPrinterAction::PrintActionExists() function in the
Common Desktop Environment 2.3.0 and earlier, as used in Oracle Solaris 10 1/13
(Update 11) and earlier, allows local users to gain root privileges via a long
printer name passed to dtprintinfo by a malicious lpstat program.

This is a 0day vulnerability demonstrated at #INFILTRATE19 on May 2nd, 2019 in
the talk "A bug's life: story of a Solaris 0day".

2. Example Attack Session.

bash-3.2$ cat /etc/release
                    Oracle Solaris 10 1/13 s10x_u11wos_24a X86
  Copyright (c) 1983, 2013, Oracle and/or its affiliates. All rights reserved.
                            Assembled 17 January 2013
bash-3.2$ uname -a
SunOS nostalgia 5.10 Generic_147148-26 i86pc i386 i86pc
bash-3.2$ id
uid=54322(raptor) gid=1(other)
bash-3.2$ gcc raptor_dtprintname_intel.c -o raptor_dtprintname_intel -Wall
bash-3.2$ ./raptor_dtprintname_intel 192.168.1.1:0
raptor_dtprintname_intel.c - dtprintinfo 0day, Solaris/Intel
Copyright (c) 2004-2019 Marco Ivaldi <raptor@0xdeadbeef.info>

Using SI_PLATFORM       : i86pc (5.10)
Using stack base        : 0x8047fff
Using rwx_mem address   : 0xfeffa004
Using sc address        : 0x8047f60
Using strcpy() address  : 0xfefe26a0

lpstat called with -v
lpstat called with -v
lpstat called with -d
uid=0(root) gid=1(other)

3. Affected Platforms.

All platforms shipping the Common Desktop Environment are potentially
affected. This includes:

* Oracle Solaris 10 1/13 (Update 11) and earlier [default installation]

According to the CDE Wiki, the following platforms are officially supported:

* All Official Ubuntu variants 12.04 - 18.04
* Debian 6, 7, 8, 9
* Fedora 17 at least
* Archlinux
* Red Hat
* Slackware 14.0
* OpenBSD
* NetBSD
* FreeBSD 9.2, 10.x, 11.x
* openSUSE Tumbleweed (gcc7)
* openSUSE Leap 4.2 (gcc4)
* SUSE 12 SP3 (gcc4)
* Solaris, OpenIndiana

4. Fix.

The upstream CDE maintainers have issued a patch for this vulnerability. Oracle
is investigating the issue via tracking# S1153109 and is expected to release a
fix for all affected-supported versions of Solaris via their quarterly Critical
Patch Update (CPU) program.

As a temporary workaround, it is possible to remove the setuid bit from the
dtprintinfo executable as follows:

bash-3.2# chmod -s /usr/dt/bin/dtprintinfo

5. Proof of Concept.

A working exploit for Oracle Solaris 10 1/13 (Update 11) Intel has been
developed as a proof of concept. Exploits for other Solaris versions and for
the SPARC architecture are also available. All exploits can be downloaded at:

https://github.com/0xdea/raptor_infiltrate19/
https://github.com/0xdea/exploits/

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