libptytty/src/proxy.C

// This file is part of libptytty. Do not make local modifications.
// http://software.schmorp.de/pkg/libptytty

/*----------------------------------------------------------------------*
 * File:        proxy.C
 *----------------------------------------------------------------------*
 *
 * All portions of code are copyright by their respective author/s.
 * Copyright (c) 2006      Marc Lehmann <schmorp@schmorp.de>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *---------------------------------------------------------------------*/

#include "config.h"

#include "ptytty.h"

#include <cstdio>
#include <cstring>
#include <csignal>

#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>

// helper/proxy support

#if PTYTTY_HELPER

static int sock_fd = -1, lock_fd = -1;
static int helper_pid, owner_pid;

struct command
{
  enum { get, login, destroy } type;

  ptytty *id;

  bool login_shell;
  int cmd_pid;
  char hostname[512]; // arbitrary, but should be plenty
};

struct ptytty_proxy : ptytty
{
  ptytty *id;

  ptytty_proxy ()
  : id(0)
  {
  }

  ~ptytty_proxy ();

  bool get ();
  void login (int cmd_pid, bool login_shell, const char *hostname);
};

#if PTYTTY_REENTRANT
# define NEED_TOKEN read  (lock_fd, &lock_fd, 1)
# define GIVE_TOKEN write (lock_fd, &lock_fd, 1)
#else
# define NEED_TOKEN (void)0
# define GIVE_TOKEN (void)0
#endif

bool
ptytty_proxy::get ()
{
  NEED_TOKEN;

  command cmd;

  cmd.type = command::get;

  write (sock_fd, &cmd, sizeof (cmd));

  if (read (sock_fd, &id, sizeof (id)) != sizeof (id))
    PTYTTY_FATAL ("protocol error while creating pty using helper process, aborting.\n");

  if (!id)
    {
      GIVE_TOKEN;
      return false;
    }

  if ((pty = recv_fd (sock_fd)) < 0
      || (tty = recv_fd (sock_fd)) < 0)
    PTYTTY_FATAL ("protocol error while reading pty/tty fds from helper process, aborting.\n");

  GIVE_TOKEN;
  return true;
}

void
ptytty_proxy::login (int cmd_pid, bool login_shell, const char *hostname)
{
  NEED_TOKEN;

  command cmd;

  cmd.type = command::login;
  cmd.id = id;
  cmd.cmd_pid = cmd_pid;
  cmd.login_shell = login_shell;
  strncpy (cmd.hostname, hostname, sizeof (cmd.hostname));

  write (sock_fd, &cmd, sizeof (cmd));

  GIVE_TOKEN;
}

ptytty_proxy::~ptytty_proxy ()
{
  if (id)
    {
      close_tty ();

      if (pty >= 0)
        close (pty);

      NEED_TOKEN;

      command cmd;

      cmd.type = command::destroy;
      cmd.id = id;

      write (sock_fd, &cmd, sizeof (cmd));

      GIVE_TOKEN;
    }
}

static
void serve ()
{
  command cmd;
  vector<ptytty *> ptys;

  for (;;)
    {
      GIVE_TOKEN;

      if (read (sock_fd, &cmd, sizeof (command)) != sizeof (command))
        break;

      if (cmd.type == command::get)
        {
          // -> id ptyfd ttyfd
          cmd.id = new ptytty_unix;

          if (cmd.id->get ())
            {
              write (sock_fd, &cmd.id, sizeof (cmd.id));
              ptys.push_back (cmd.id);

              ptytty::send_fd (sock_fd, cmd.id->pty);
              ptytty::send_fd (sock_fd, cmd.id->tty);
            }
          else
            {
              delete cmd.id;
              cmd.id = 0;
              write (sock_fd, &cmd.id, sizeof (cmd.id));
            }
        }
      else if (cmd.type == command::login)
        {
#if UTMP_SUPPORT
          if (find (ptys.begin (), ptys.end (), cmd.id) != ptys.end ())
            {
              cmd.hostname[sizeof (cmd.hostname) - 1] = 0;
              cmd.id->login (cmd.cmd_pid, cmd.login_shell, cmd.hostname);
            }
#endif
        }
      else if (cmd.type == command::destroy)
        {
          vector<ptytty *>::iterator pty = find (ptys.begin (), ptys.end (), cmd.id);

          if (pty != ptys.end ())
            {
              delete *pty;
              ptys.erase (pty);
            }
        }
      else
        break;

      NEED_TOKEN;
    }

  // destroy all ptys
  for (vector<ptytty *>::iterator i = ptys.end (); i-- > ptys.begin (); )
    delete *i;
}

void
ptytty::use_helper ()
{
#ifndef PTYTTY_NO_PID_CHECK
  int pid = getpid ();
#endif

  if (sock_fd >= 0
#ifndef PTYTTY_NO_PID_CHECK
      && pid == owner_pid
#endif
      )
    return;

#ifndef PTYTTY_NO_PID_CHECK
  owner_pid = pid;
#endif

  int sv[2];

  if (socketpair (AF_UNIX, SOCK_STREAM, 0, sv))
    PTYTTY_FATAL ("could not create socket to communicate with pty/sessiondb helper, aborting.\n");

#if PTYTTY_REENTRANT
  int lv[2];

  if (socketpair (AF_UNIX, SOCK_STREAM, 0, lv))
    PTYTTY_FATAL ("could not create socket to communicate with pty/sessiondb helper, aborting.\n");
#endif

  helper_pid = fork ();

  if (helper_pid < 0)
    PTYTTY_FATAL ("could not create pty/sessiondb helper process, aborting.\n");

  if (helper_pid)
    {
      // client, process
      sock_fd = sv[0];
      close (sv[1]);
      fcntl (sock_fd, F_SETFD, FD_CLOEXEC);
#if PTYTTY_REENTRANT
      lock_fd = lv[0];
      close (lv[1]);
      fcntl (lock_fd, F_SETFD, FD_CLOEXEC);
#endif
    }
  else
    {
      // server, pty-helper
      sock_fd = sv[1];
#if PTYTTY_REENTRANT
      lock_fd = lv[1];
#endif

      chdir ("/");

      signal (SIGHUP,  SIG_IGN);
      signal (SIGTERM, SIG_IGN);
      signal (SIGINT,  SIG_IGN);
      signal (SIGPIPE, SIG_IGN);

      for (int fd = 0; fd < 1023; fd++)
        if (fd != sock_fd && fd != lock_fd)
          close (fd);

      serve ();
      _exit (EXIT_SUCCESS);
    }
}

#endif

ptytty *
ptytty::create ()
{
#if PTYTTY_HELPER
  if (helper_pid
# ifndef PTYTTY_NO_PID_CHECK
      && getpid () == owner_pid
# endif
      )
    // use helper process
    return new ptytty_proxy;
  else
#endif
    return new ptytty_unix;
}

void
ptytty::sanitise_stdfd ()
{
  // sanitise stdin/stdout/stderr to point to *something*.
  for (int fd = 0; fd <= 2; ++fd)
    if (fcntl (fd, F_GETFL) < 0 && errno == EBADF)
      {
        int fd2 = open ("/dev/tty", fd ? O_WRONLY : O_RDONLY);

        if (fd2 < 0)
          fd2 = open ("/dev/null", fd ? O_WRONLY : O_RDONLY);

        if (fd2 != fd)
          abort ();
      }
}

void
ptytty::init ()
{
  sanitise_stdfd ();

  uid_t uid = getuid ();
  gid_t gid = getgid ();

  // before doing anything else, check for setuid/setgid operation,
  // start the helper process and drop privileges
  if (uid != geteuid ()
      || gid != getegid ())
    {
#if PTYTTY_HELPER
      use_helper ();
#else
      PTYTTY_WARN ("running setuid/setgid without pty helper compiled in, continuing unprivileged.\n", 0);
#endif

      drop_privileges ();
    }
}

void
ptytty::drop_privileges ()
{
  uid_t uid = getuid ();
  gid_t gid = getgid ();

  // drop privileges
#if HAVE_SETRESUID
  setresgid (gid, gid, gid);
  setresuid (uid, uid, uid);
#elif HAVE_SETREUID
  setregid (gid, gid);
  setreuid (uid, uid);
#elif HAVE_SETUID
  setgid (gid);
  setuid (uid);
#else
# error no way to drop privileges, configure failed?
#endif

  if (uid != geteuid ()
      || gid != getegid ())
    PTYTTY_FATAL ("unable to drop privileges, aborting.\n");
}

Revision:	1.12
Committed:	Mon Jun 20 11:29:11 2011 UTC (15 years, 2 months ago) by sf-exg
Content type:	text/plain
Branch:	MAIN
CVS Tags:	rel-9_12, rel-1_4
Changes since 1.11:	+3 -3 lines
Log Message:	Use if rather than ifdef for PTYTTY_REENTRANT blocks.
#	Content
1	// This file is part of libptytty. Do not make local modifications.
2	// http://software.schmorp.de/pkg/libptytty
3
4	/----------------------------------------------------------------------
5	* File: proxy.C
6	----------------------------------------------------------------------
7	*
8	* All portions of code are copyright by their respective author/s.
9	* Copyright (c) 2006 Marc Lehmann <schmorp@schmorp.de>
10	*
11	* This program is free software; you can redistribute it and/or modify
12	* it under the terms of the GNU General Public License as published by
13	* the Free Software Foundation; either version 2 of the License, or
14	* (at your option) any later version.
15	*
16	* This program is distributed in the hope that it will be useful,
17	* but WITHOUT ANY WARRANTY; without even the implied warranty of
18	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19	* GNU General Public License for more details.
20	*
21	* You should have received a copy of the GNU General Public License
22	* along with this program; if not, write to the Free Software
23	* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
24	---------------------------------------------------------------------/
25
26	#include "config.h"
27
28	#include "ptytty.h"
29
30	#include <cstdio>
31	#include <cstring>
32	#include <csignal>
33
34	#include <sys/types.h>
35	#include <sys/socket.h>
36	#include <unistd.h>
37	#include <fcntl.h>
38	#include <errno.h>
39
40	// helper/proxy support
41
42	#if PTYTTY_HELPER
43
44	static int sock_fd = -1, lock_fd = -1;
45	static int helper_pid, owner_pid;
46
47	struct command
48	{
49	enum { get, login, destroy } type;
50
51	ptytty *id;
52
53	bool login_shell;
54	int cmd_pid;
55	char hostname[512]; // arbitrary, but should be plenty
56	};
57
58	struct ptytty_proxy : ptytty
59	{
60	ptytty *id;
61
62	ptytty_proxy ()
63	: id(0)
64	{
65	}
66
67	~ptytty_proxy ();
68
69	bool get ();
70	void login (int cmd_pid, bool login_shell, const char *hostname);
71	};
72
73	#if PTYTTY_REENTRANT
74	# define NEED_TOKEN read (lock_fd, &lock_fd, 1)
75	# define GIVE_TOKEN write (lock_fd, &lock_fd, 1)
76	#else
77	# define NEED_TOKEN (void)0
78	# define GIVE_TOKEN (void)0
79	#endif
80
81	bool
82	ptytty_proxy::get ()
83	{
84	NEED_TOKEN;
85
86	command cmd;
87
88	cmd.type = command::get;
89
90	write (sock_fd, &cmd, sizeof (cmd));
91
92	if (read (sock_fd, &id, sizeof (id)) != sizeof (id))
93	PTYTTY_FATAL ("protocol error while creating pty using helper process, aborting.\n");
94
95	if (!id)
96	{
97	GIVE_TOKEN;
98	return false;
99	}
100
101	if ((pty = recv_fd (sock_fd)) < 0
102	\|\| (tty = recv_fd (sock_fd)) < 0)
103	PTYTTY_FATAL ("protocol error while reading pty/tty fds from helper process, aborting.\n");
104
105	GIVE_TOKEN;
106	return true;
107	}
108
109	void
110	ptytty_proxy::login (int cmd_pid, bool login_shell, const char *hostname)
111	{
112	NEED_TOKEN;
113
114	command cmd;
115
116	cmd.type = command::login;
117	cmd.id = id;
118	cmd.cmd_pid = cmd_pid;
119	cmd.login_shell = login_shell;
120	strncpy (cmd.hostname, hostname, sizeof (cmd.hostname));
121
122	write (sock_fd, &cmd, sizeof (cmd));
123
124	GIVE_TOKEN;
125	}
126
127	ptytty_proxy::~ptytty_proxy ()
128	{
129	if (id)
130	{
131	close_tty ();
132
133	if (pty >= 0)
134	close (pty);
135
136	NEED_TOKEN;
137
138	command cmd;
139
140	cmd.type = command::destroy;
141	cmd.id = id;
142
143	write (sock_fd, &cmd, sizeof (cmd));
144
145	GIVE_TOKEN;
146	}
147	}
148
149	static
150	void serve ()
151	{
152	command cmd;
153	vector<ptytty *> ptys;
154
155	for (;;)
156	{
157	GIVE_TOKEN;
158
159	if (read (sock_fd, &cmd, sizeof (command)) != sizeof (command))
160	break;
161
162	if (cmd.type == command::get)
163	{
164	// -> id ptyfd ttyfd
165	cmd.id = new ptytty_unix;
166
167	if (cmd.id->get ())
168	{
169	write (sock_fd, &cmd.id, sizeof (cmd.id));
170	ptys.push_back (cmd.id);
171
172	ptytty::send_fd (sock_fd, cmd.id->pty);
173	ptytty::send_fd (sock_fd, cmd.id->tty);
174	}
175	else
176	{
177	delete cmd.id;
178	cmd.id = 0;
179	write (sock_fd, &cmd.id, sizeof (cmd.id));
180	}
181	}
182	else if (cmd.type == command::login)
183	{
184	#if UTMP_SUPPORT
185	if (find (ptys.begin (), ptys.end (), cmd.id) != ptys.end ())
186	{
187	cmd.hostname[sizeof (cmd.hostname) - 1] = 0;
188	cmd.id->login (cmd.cmd_pid, cmd.login_shell, cmd.hostname);
189	}
190	#endif
191	}
192	else if (cmd.type == command::destroy)
193	{
194	vector<ptytty *>::iterator pty = find (ptys.begin (), ptys.end (), cmd.id);
195
196	if (pty != ptys.end ())
197	{
198	delete *pty;
199	ptys.erase (pty);
200	}
201	}
202	else
203	break;
204
205	NEED_TOKEN;
206	}
207
208	// destroy all ptys
209	for (vector<ptytty *>::iterator i = ptys.end (); i-- > ptys.begin (); )
210	delete *i;
211	}
212
213	void
214	ptytty::use_helper ()
215	{
216	#ifndef PTYTTY_NO_PID_CHECK
217	int pid = getpid ();
218	#endif
219
220	if (sock_fd >= 0
221	#ifndef PTYTTY_NO_PID_CHECK
222	&& pid == owner_pid
223	#endif
224	)
225	return;
226
227	#ifndef PTYTTY_NO_PID_CHECK
228	owner_pid = pid;
229	#endif
230
231	int sv[2];
232
233	if (socketpair (AF_UNIX, SOCK_STREAM, 0, sv))
234	PTYTTY_FATAL ("could not create socket to communicate with pty/sessiondb helper, aborting.\n");
235
236	#if PTYTTY_REENTRANT
237	int lv[2];
238
239	if (socketpair (AF_UNIX, SOCK_STREAM, 0, lv))
240	PTYTTY_FATAL ("could not create socket to communicate with pty/sessiondb helper, aborting.\n");
241	#endif
242
243	helper_pid = fork ();
244
245	if (helper_pid < 0)
246	PTYTTY_FATAL ("could not create pty/sessiondb helper process, aborting.\n");
247
248	if (helper_pid)
249	{
250	// client, process
251	sock_fd = sv[0];
252	close (sv[1]);
253	fcntl (sock_fd, F_SETFD, FD_CLOEXEC);
254	#if PTYTTY_REENTRANT
255	lock_fd = lv[0];
256	close (lv[1]);
257	fcntl (lock_fd, F_SETFD, FD_CLOEXEC);
258	#endif
259	}
260	else
261	{
262	// server, pty-helper
263	sock_fd = sv[1];
264	#if PTYTTY_REENTRANT
265	lock_fd = lv[1];
266	#endif
267
268	chdir ("/");
269
270	signal (SIGHUP, SIG_IGN);
271	signal (SIGTERM, SIG_IGN);
272	signal (SIGINT, SIG_IGN);
273	signal (SIGPIPE, SIG_IGN);
274
275	for (int fd = 0; fd < 1023; fd++)
276	if (fd != sock_fd && fd != lock_fd)
277	close (fd);
278
279	serve ();
280	_exit (EXIT_SUCCESS);
281	}
282	}
283
284	#endif
285
286	ptytty *
287	ptytty::create ()
288	{
289	#if PTYTTY_HELPER
290	if (helper_pid
291	# ifndef PTYTTY_NO_PID_CHECK
292	&& getpid () == owner_pid
293	# endif
294	)
295	// use helper process
296	return new ptytty_proxy;
297	else
298	#endif
299	return new ptytty_unix;
300	}
301
302	void
303	ptytty::sanitise_stdfd ()
304	{
305	// sanitise stdin/stdout/stderr to point to something.
306	for (int fd = 0; fd <= 2; ++fd)
307	if (fcntl (fd, F_GETFL) < 0 && errno == EBADF)
308	{
309	int fd2 = open ("/dev/tty", fd ? O_WRONLY : O_RDONLY);
310
311	if (fd2 < 0)
312	fd2 = open ("/dev/null", fd ? O_WRONLY : O_RDONLY);
313
314	if (fd2 != fd)
315	abort ();
316	}
317	}
318
319	void
320	ptytty::init ()
321	{
322	sanitise_stdfd ();
323
324	uid_t uid = getuid ();
325	gid_t gid = getgid ();
326
327	// before doing anything else, check for setuid/setgid operation,
328	// start the helper process and drop privileges
329	if (uid != geteuid ()
330	\|\| gid != getegid ())
331	{
332	#if PTYTTY_HELPER
333	use_helper ();
334	#else
335	PTYTTY_WARN ("running setuid/setgid without pty helper compiled in, continuing unprivileged.\n", 0);
336	#endif
337
338	drop_privileges ();
339	}
340	}
341
342	void
343	ptytty::drop_privileges ()
344	{
345	uid_t uid = getuid ();
346	gid_t gid = getgid ();
347
348	// drop privileges
349	#if HAVE_SETRESUID
350	setresgid (gid, gid, gid);
351	setresuid (uid, uid, uid);
352	#elif HAVE_SETREUID
353	setregid (gid, gid);
354	setreuid (uid, uid);
355	#elif HAVE_SETUID
356	setgid (gid);
357	setuid (uid);
358	#else
359	# error no way to drop privileges, configure failed?
360	#endif
361
362	if (uid != geteuid ()
363	\|\| gid != getegid ())
364	PTYTTY_FATAL ("unable to drop privileges, aborting.\n");
365	}
366