CVE-2013-2207, BZ #15755: Disable pt_chown.

The helper binary pt_chown tricked into granting access to another
user's pseudo-terminal.

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

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.

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 hte use of pt_chown but distributions do so at their own
risk.

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>