From 5d96012d9978efe4bad88a38e2efcbeada9f7585 Mon Sep 17 00:00:00 2001
From: mancha <mancha1@hush.com>
Date: Thu, 22 Aug 2013
Subject: CVE-2013-2207, BZ #15755: Disable pt_chown.
Using the setuid installed pt_chown and a weak check on whether a file
descriptor is a tty, an attacker could fake a pty check using FUSE and
trick pt_chown to grant ownership of a pty descriptor that the current
user does not own. It cannot access /dev/pts/ptmx however.
Pre-conditions for the attack:
* Attacker with local user account
* Kernel with FUSE support
* "user_allow_other" in /etc/fuse.conf
* Victim with allocated slave in /dev/pts
In most modern distributions pt_chown is not needed because devpts
is enabled by default. The fix for this CVE is to disable building
and using pt_chown by default. We still provide a configure option
to enable the use of pt_chown but distributions do so at their own
risk.
---
This patch was adapted for glibc 2.17 point release from:
http://sourceware.org/git/?p=glibc.git;a=commit;h=e4608715e6e1
---
INSTALL | 12 ++++++++++++
config.h.in | 3 +++
config.make.in | 1 +
configure | 15 +++++++++++++++
configure.in | 10 ++++++++++
login/Makefile | 8 +++++++-
manual/install.texi | 14 ++++++++++++++
sysdeps/unix/grantpt.c | 8 +++++---
sysdeps/unix/sysv/linux/grantpt.c | 5 +++--
9 files changed, 70 insertions(+), 6 deletions(-)
---
--- a/INSTALL
+++ b/INSTALL
@@ -128,6 +128,18 @@ will be used, and CFLAGS sets optimizati
this can be prevented though there generally is no reason since it
creates compatibility problems.
+`--enable-pt_chown'
+ The file `pt_chown' is a helper binary for `grantpt' (*note
+ Pseudo-Terminals: Allocation.) that is installed setuid root to
+ fix up pseudo-terminal ownership. It is not built by default
+ because systems using the Linux kernel are commonly built with the
+ `devpts' filesystem enabled and mounted at `/dev/pts', which
+ manages pseudo-terminal ownership automatically. By using
+ `--enable-pt_chown', you may build `pt_chown' and install it
+ setuid and owned by `root'. The use of `pt_chown' introduces
+ additional security risks to the system and you should enable it
+ only if you understand and accept those risks.
+
`--build=BUILD-SYSTEM'
`--host=HOST-SYSTEM'
These options are for cross-compiling. If you specify both
--- a/config.h.in
+++ b/config.h.in
@@ -232,4 +232,7 @@
/* The ARM hard-float ABI is being used. */
#undef HAVE_ARM_PCS_VFP
+/* The pt_chown binary is being built and used by grantpt. */
+#undef HAVE_PT_CHOWN
+
#endif
--- a/config.make.in
+++ b/config.make.in
@@ -101,6 +101,7 @@ force-install = @force_install@
link-obsolete-rpc = @link_obsolete_rpc@
build-nscd = @build_nscd@
use-nscd = @use_nscd@
+build-pt-chown = @build_pt_chown@
# Build tools.
CC = @CC@
--- a/configure
+++ b/configure
@@ -653,6 +653,7 @@ multi_arch
base_machine
add_on_subdirs
add_ons
+build_pt_chown
build_nscd
link_obsolete_rpc
libc_cv_nss_crypt
@@ -759,6 +760,7 @@ enable_obsolete_rpc
enable_systemtap
enable_build_nscd
enable_nscd
+enable_pt_chown
with_cpu
'
ac_precious_vars='build_alias
@@ -1419,6 +1421,7 @@ Optional Features:
--enable-systemtap enable systemtap static probe points [default=no]
--disable-build-nscd disable building and installing the nscd daemon
--disable-nscd library functions will not contact the nscd daemon
+ --enable-pt_chown Enable building and installing pt_chown
Optional Packages:
--with-PACKAGE[=ARG] use PACKAGE [ARG=yes]
@@ -3933,6 +3936,18 @@ else
use_nscd=yes
fi
+# Check whether --enable-pt_chown was given.
+if test "${enable_pt_chown+set}" = set; then :
+ enableval=$enable_pt_chown; build_pt_chown=$enableval
+else
+ build_pt_chown=no
+fi
+
+
+if test $build_pt_chown = yes; then
+ $as_echo "#define HAVE_PT_CHOWN 1" >>confdefs.h
+
+fi
# The way shlib-versions is used to generate soversions.mk uses a
# fairly simplistic model for name recognition that can't distinguish
--- a/configure.in
+++ b/configure.in
@@ -315,6 +315,16 @@ AC_ARG_ENABLE([nscd],
[use_nscd=$enableval],
[use_nscd=yes])
+AC_ARG_ENABLE([pt_chown],
+ [AS_HELP_STRING([--enable-pt_chown],
+ [Enable building and installing pt_chown])],
+ [build_pt_chown=$enableval],
+ [build_pt_chown=no])
+AC_SUBST(build_pt_chown)
+if test $build_pt_chown = yes; then
+ AC_DEFINE(HAVE_PT_CHOWN)
+fi
+
# The way shlib-versions is used to generate soversions.mk uses a
# fairly simplistic model for name recognition that can't distinguish
# i486-pc-linux-gnu fully from i486-pc-gnu. So we mutate a $host_os
--- a/login/Makefile
+++ b/login/Makefile
@@ -29,9 +29,15 @@ routines := getutent getutent_r getutid
CFLAGS-grantpt.c = -DLIBEXECDIR='"$(libexecdir)"'
-others = utmpdump pt_chown
+others = utmpdump
+
+include ../Makeconfig
+
+ifeq (yes,$(build-pt-chown))
+others += pt_chown
others-pie = pt_chown
install-others-programs = $(inst_libexecdir)/pt_chown
+endif
subdir-dirs = programs
vpath %.c programs
--- a/manual/install.texi
+++ b/manual/install.texi
@@ -155,6 +155,20 @@ if the used tools support it. By using
prevented though there generally is no reason since it creates
compatibility problems.
+@pindex pt_chown
+@findex grantpt
+@item --enable-pt_chown
+The file @file{pt_chown} is a helper binary for @code{grantpt}
+(@pxref{Allocation, Pseudo-Terminals}) that is installed setuid root to
+fix up pseudo-terminal ownership. It is not built by default because
+systems using the Linux kernel are commonly built with the @code{devpts}
+filesystem enabled and mounted at @file{/dev/pts}, which manages
+pseudo-terminal ownership automatically. By using
+@samp{--enable-pt_chown}, you may build @file{pt_chown} and install it
+setuid and owned by @code{root}. The use of @file{pt_chown} introduces
+additional security risks to the system and you should enable it only if
+you understand and accept those risks.
+
@item --build=@var{build-system}
@itemx --host=@var{host-system}
These options are for cross-compiling. If you specify both options and
--- a/sysdeps/unix/grantpt.c
+++ b/sysdeps/unix/grantpt.c
@@ -173,9 +173,10 @@ grantpt (int fd)
retval = 0;
goto cleanup;
- /* We have to use the helper program. */
+ /* We have to use the helper program if it is available.. */
helper:;
+#ifdef HAVE_PT_CHOWN
pid_t pid = __fork ();
if (pid == -1)
goto cleanup;
@@ -190,9 +191,9 @@ grantpt (int fd)
if (__dup2 (fd, PTY_FILENO) < 0)
_exit (FAIL_EBADF);
-#ifdef CLOSE_ALL_FDS
+# ifdef CLOSE_ALL_FDS
CLOSE_ALL_FDS ();
-#endif
+# endif
execle (_PATH_PT_CHOWN, basename (_PATH_PT_CHOWN), NULL, NULL);
_exit (FAIL_EXEC);
@@ -231,6 +232,7 @@ grantpt (int fd)
assert(! "getpt: internal error: invalid exit code from pt_chown");
}
}
+#endif
cleanup:
if (buf != _buf)
--- a/sysdeps/unix/sysv/linux/grantpt.c
+++ b/sysdeps/unix/sysv/linux/grantpt.c
@@ -11,7 +11,7 @@
#include "pty-private.h"
-
+#if HAVE_PT_CHOWN
/* Close all file descriptors except the one specified. */
static void
close_all_fds (void)
@@ -38,6 +38,7 @@ close_all_fds (void)
__dup2 (STDOUT_FILENO, STDERR_FILENO);
}
}
-#define CLOSE_ALL_FDS() close_all_fds()
+# define CLOSE_ALL_FDS() close_all_fds()
+#endif
#include <sysdeps/unix/grantpt.c>
