Implement POSIX grantpt(3) functionality, and add a pt_chown utility (akin

to Solaris, it is in /usr/libexec) to perform the handing over of tty nodes
to the user being granted the pty.

Submitted by:	Ryan Younce <ryany@pobox.com>
Reviewed by:	security-officer@, standards@, mike@

2 files changed, 112 insertions, 0 deletions

diff --git a/libexec/pt_chown/Makefile b/libexec/pt_chown/Makefile
new file mode 100644
index 0000000..974a730f
--- /dev/null
+++ b/libexec/pt_chown/Makefile
@@ -0,0 +1,9 @@
+# $FreeBSD$
+
+PROG=	pt_chown
+SRCS=	pt_chown.c
+BINOWN=	root
+BINMODE=4555
+NOMAN=	yes
+
+.include <bsd.prog.mk>
diff --git a/libexec/pt_chown/pt_chown.c b/libexec/pt_chown/pt_chown.c
new file mode 100644
index 0000000..d89ffea
--- /dev/null
+++ b/libexec/pt_chown/pt_chown.c
@@ -0,0 +1,103 @@
+/*
+ * Copyright (c) 2002 The FreeBSD Project, Inc.
+ * All rights reserved.
+ *
+ * This software includes code contributed to the FreeBSD Project
+ * by Ryan Younce of North Carolina State University.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the FreeBSD Project nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE FREEBSD PROJECT AND CONTRIBUTORS ``AS IS''
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE FREEBSD PROJECT OR ITS CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+#ifndef lint
+__FBSDID("$FreeBSD$");
+#endif /* not lint */
+
+#include <sys/stat.h>
+
+#include <grp.h>
+#include <stdlib.h>
+#include <sysexits.h>
+#include <unistd.h>
+
+/*
+ * pt_chown
+ * Utility support routine for grantpt(3).
+ *
+ * According to IEEE Std 1003.1-2001, grantpt(3) changes ownership and
+ * permission bits of a slave pseudo-terminal device associated with a
+ * master.
+ *
+ * Since doing this if we are not the owner of the slave (which would
+ * rarely happen) cannot be done by conventional methods, grantpt(3)
+ * has to rely on this support program, which is setuid root, to change
+ * the slave's owner, group, and permission mode attributes.  It's
+ * a rather undesirable approach, but Digital Unix and Solaris also seem
+ * to rely on this approach to pull this off.
+ *
+ * This program hangs around long enough to do just these things upon
+ * its standard input (which is set up by grantpt(3) to be the master's
+ * descriptor, the one passed to it).  The rationale behind this
+ * approach not allowing somebody to modify ownership of another active
+ * pseudo terminal is:
+ *
+ * 1)  This program only operates on its standard input.  If STDIN_FILENO
+ *     is not open or is not a pseudo-terminal master, no action is
+ *     taken and the program exits (ptsname() is called for a non-NULL
+ *     return).
+ * 2)  Only one active file description for a pseudo-terminal master
+ *     can exist at a time (attempting to open an active PTY returns with
+ *     EIO - I/O Error).  Thus, if the pseudo-terminal is already in
+ *     use by somebody else, it could not have been opened to begin
+ *     with, and thus this program would be useless in such situations.
+ */
+int
+main(int argc, char *argv[])
+{
+	int retcode;
+	char *slave;
+	gid_t gid;
+	struct group *grp;
+
+	retcode = EX_OK;
+
+	if ((slave = ptsname(STDIN_FILENO)) == NULL)
+		retcode = EX_USAGE;
+	else {
+		gid = (grp = getgrnam("tty")) ? grp->gr_gid : -1;
+		if (chown(slave, getuid(), gid) == 0 &&
+		    chmod(slave, S_IRUSR | S_IWUSR | S_IWGRP) == 0)
+			retcode = 0;
+		else
+			retcode = EX_NOPERM;
+	}
+
+	/*
+	 * grantpt(3) checks the retcode for being either zero or
+	 * nonzero.  Any nonzero return results in errno being set
+	 * to EACCES.
+	 */
+	exit(retcode);
+}