From e4608715e6e1dd2adc91982fd151d5ba4f761d69 Mon Sep 17 00:00:00 2001
From: Carlos O'Donell <carlos@redhat.com>
Date: Fri, 19 Jul 2013 02:42:03 -0400
Subject: 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/grantpt.c            | 8 +++++---
 sysdeps/unix/sysv/linux/grantpt.c | 5 +++--
 2 files changed, 8 insertions(+), 5 deletions(-)

(limited to 'sysdeps/unix')

diff --git a/sysdeps/unix/grantpt.c b/sysdeps/unix/grantpt.c
index d37da13506..431be855a3 100644
--- 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)
diff --git a/sysdeps/unix/sysv/linux/grantpt.c b/sysdeps/unix/sysv/linux/grantpt.c
index 0a3cd472fa..8cebde36ed 100644
--- 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>
-- 
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