libptytty/src/proxy.C

/*----------------------------------------------------------------------*
 * 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 "estl.h"

#include <stdio.h>
#include <string.h>
#include <signal.h>

#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;

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 do { char ch; read  (lock_fd, &ch     , 1); } while (0)
# 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);

              cmd.id->close_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 ()
{
  if (sock_fd >= 0)
    return;

  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)
    // 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)
          PTYTTY_FATAL ("unable to sanitise fds, aborting.\n");
      }
}

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");
#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:	1.25
Committed:	Wed Jun 16 05:08:48 2021 UTC (5 years, 3 months ago) by sf-exg
Content type:	text/plain
Branch:	MAIN
Changes since 1.24:	+2 -2 lines
Log Message:	Fix style
#	User	Rev	Content
1	root	1.1	/----------------------------------------------------------------------
2			* File: proxy.C
3			----------------------------------------------------------------------
4			*
5			* All portions of code are copyright by their respective author/s.
6	sf-exg	1.9	* Copyright (c) 2006 Marc Lehmann <schmorp@schmorp.de>
7	root	1.1	*
8			* This program is free software; you can redistribute it and/or modify
9			* it under the terms of the GNU General Public License as published by
10	sf-exg	1.20	* the Free Software Foundation; either version 2 of the License, or
11	root	1.1	* (at your option) any later version.
12			*
13			* This program is distributed in the hope that it will be useful,
14			* but WITHOUT ANY WARRANTY; without even the implied warranty of
15			* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16			* GNU General Public License for more details.
17			*
18			* You should have received a copy of the GNU General Public License
19			* along with this program; if not, write to the Free Software
20			* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
21			---------------------------------------------------------------------/
22
23	sf-exg	1.8	#include "config.h"
24	root	1.1
25			#include "ptytty.h"
26
27	sf-exg	1.16	#include "estl.h"
28	sf-exg	1.13
29	sf-exg	1.15	#include <stdio.h>
30			#include <string.h>
31			#include <signal.h>
32	root	1.1
33			#include <sys/types.h>
34			#include <sys/socket.h>
35			#include <unistd.h>
36			#include <fcntl.h>
37	root	1.4	#include <errno.h>
38	root	1.1
39			// helper/proxy support
40
41			#if PTYTTY_HELPER
42
43			static int sock_fd = -1, lock_fd = -1;
44	root	1.18	static int helper_pid;
45	root	1.1
46			struct command
47			{
48			enum { get, login, destroy } type;
49
50			ptytty *id;
51
52			bool login_shell;
53			int cmd_pid;
54			char hostname[512]; // arbitrary, but should be plenty
55			};
56
57			struct ptytty_proxy : ptytty
58			{
59			ptytty *id;
60
61			ptytty_proxy ()
62			: id(0)
63			{
64			}
65
66			~ptytty_proxy ();
67
68			bool get ();
69			void login (int cmd_pid, bool login_shell, const char *hostname);
70			};
71
72			#if PTYTTY_REENTRANT
73	root	1.23	# define NEED_TOKEN do { char ch; read (lock_fd, &ch , 1); } while (0)
74			# define GIVE_TOKEN write (lock_fd, &lock_fd, 1)
75	root	1.1	#else
76			# define NEED_TOKEN (void)0
77			# define GIVE_TOKEN (void)0
78			#endif
79
80			bool
81			ptytty_proxy::get ()
82			{
83			NEED_TOKEN;
84
85			command cmd;
86
87			cmd.type = command::get;
88
89			write (sock_fd, &cmd, sizeof (cmd));
90
91			if (read (sock_fd, &id, sizeof (id)) != sizeof (id))
92	sf-exg	1.10	PTYTTY_FATAL ("protocol error while creating pty using helper process, aborting.\n");
93	root	1.1
94			if (!id)
95			{
96			GIVE_TOKEN;
97			return false;
98			}
99
100			if ((pty = recv_fd (sock_fd)) < 0
101			\|\| (tty = recv_fd (sock_fd)) < 0)
102	sf-exg	1.10	PTYTTY_FATAL ("protocol error while reading pty/tty fds from helper process, aborting.\n");
103	root	1.1
104			GIVE_TOKEN;
105			return true;
106			}
107
108			void
109			ptytty_proxy::login (int cmd_pid, bool login_shell, const char *hostname)
110			{
111			NEED_TOKEN;
112
113			command cmd;
114
115			cmd.type = command::login;
116			cmd.id = id;
117			cmd.cmd_pid = cmd_pid;
118			cmd.login_shell = login_shell;
119			strncpy (cmd.hostname, hostname, sizeof (cmd.hostname));
120
121			write (sock_fd, &cmd, sizeof (cmd));
122
123			GIVE_TOKEN;
124			}
125
126			ptytty_proxy::~ptytty_proxy ()
127			{
128			if (id)
129			{
130	ayin	1.3	close_tty ();
131
132			if (pty >= 0)
133			close (pty);
134	ayin	1.2
135	root	1.1	NEED_TOKEN;
136
137			command cmd;
138
139			cmd.type = command::destroy;
140			cmd.id = id;
141
142			write (sock_fd, &cmd, sizeof (cmd));
143
144			GIVE_TOKEN;
145			}
146			}
147
148	sf-exg	1.25	static void
149			serve ()
150	root	1.1	{
151			command cmd;
152			vector<ptytty *> ptys;
153
154			for (;;)
155			{
156			GIVE_TOKEN;
157
158			if (read (sock_fd, &cmd, sizeof (command)) != sizeof (command))
159			break;
160
161			if (cmd.type == command::get)
162			{
163			// -> id ptyfd ttyfd
164			cmd.id = new ptytty_unix;
165
166			if (cmd.id->get ())
167			{
168			write (sock_fd, &cmd.id, sizeof (cmd.id));
169			ptys.push_back (cmd.id);
170
171			ptytty::send_fd (sock_fd, cmd.id->pty);
172			ptytty::send_fd (sock_fd, cmd.id->tty);
173	sf-exg	1.21
174			cmd.id->close_tty ();
175	root	1.1	}
176			else
177			{
178			delete cmd.id;
179			cmd.id = 0;
180			write (sock_fd, &cmd.id, sizeof (cmd.id));
181			}
182			}
183			else if (cmd.type == command::login)
184			{
185			#if UTMP_SUPPORT
186			if (find (ptys.begin (), ptys.end (), cmd.id) != ptys.end ())
187			{
188			cmd.hostname[sizeof (cmd.hostname) - 1] = 0;
189			cmd.id->login (cmd.cmd_pid, cmd.login_shell, cmd.hostname);
190			}
191			#endif
192			}
193			else if (cmd.type == command::destroy)
194			{
195			vector<ptytty *>::iterator pty = find (ptys.begin (), ptys.end (), cmd.id);
196
197			if (pty != ptys.end ())
198			{
199			delete *pty;
200			ptys.erase (pty);
201			}
202			}
203			else
204			break;
205
206			NEED_TOKEN;
207			}
208
209			// destroy all ptys
210			for (vector<ptytty *>::iterator i = ptys.end (); i-- > ptys.begin (); )
211			delete *i;
212			}
213
214			void
215			ptytty::use_helper ()
216			{
217	root	1.18	if (sock_fd >= 0)
218	root	1.1	return;
219
220			int sv[2];
221
222			if (socketpair (AF_UNIX, SOCK_STREAM, 0, sv))
223	sf-exg	1.10	PTYTTY_FATAL ("could not create socket to communicate with pty/sessiondb helper, aborting.\n");
224	root	1.1
225	sf-exg	1.12	#if PTYTTY_REENTRANT
226	root	1.1	int lv[2];
227
228			if (socketpair (AF_UNIX, SOCK_STREAM, 0, lv))
229	sf-exg	1.10	PTYTTY_FATAL ("could not create socket to communicate with pty/sessiondb helper, aborting.\n");
230	root	1.1	#endif
231
232			helper_pid = fork ();
233
234			if (helper_pid < 0)
235	sf-exg	1.10	PTYTTY_FATAL ("could not create pty/sessiondb helper process, aborting.\n");
236	root	1.1
237			if (helper_pid)
238			{
239			// client, process
240			sock_fd = sv[0];
241			close (sv[1]);
242			fcntl (sock_fd, F_SETFD, FD_CLOEXEC);
243	sf-exg	1.12	#if PTYTTY_REENTRANT
244	root	1.1	lock_fd = lv[0];
245			close (lv[1]);
246			fcntl (lock_fd, F_SETFD, FD_CLOEXEC);
247			#endif
248			}
249			else
250			{
251			// server, pty-helper
252			sock_fd = sv[1];
253	sf-exg	1.12	#if PTYTTY_REENTRANT
254	root	1.1	lock_fd = lv[1];
255			#endif
256
257			chdir ("/");
258
259			signal (SIGHUP, SIG_IGN);
260			signal (SIGTERM, SIG_IGN);
261			signal (SIGINT, SIG_IGN);
262			signal (SIGPIPE, SIG_IGN);
263
264			for (int fd = 0; fd < 1023; fd++)
265			if (fd != sock_fd && fd != lock_fd)
266			close (fd);
267
268			serve ();
269			_exit (EXIT_SUCCESS);
270			}
271			}
272
273			#endif
274
275			ptytty *
276			ptytty::create ()
277			{
278			#if PTYTTY_HELPER
279	root	1.18	if (helper_pid)
280	root	1.1	// use helper process
281			return new ptytty_proxy;
282			else
283			#endif
284			return new ptytty_unix;
285			}
286
287			void
288	root	1.4	ptytty::sanitise_stdfd ()
289			{
290			// sanitise stdin/stdout/stderr to point to something.
291			for (int fd = 0; fd <= 2; ++fd)
292			if (fcntl (fd, F_GETFL) < 0 && errno == EBADF)
293			{
294			int fd2 = open ("/dev/tty", fd ? O_WRONLY : O_RDONLY);
295
296			if (fd2 < 0)
297	root	1.5	fd2 = open ("/dev/null", fd ? O_WRONLY : O_RDONLY);
298	root	1.4
299			if (fd2 != fd)
300	sf-exg	1.24	PTYTTY_FATAL ("unable to sanitise fds, aborting.\n");
301	root	1.4	}
302			}
303
304			void
305	root	1.1	ptytty::init ()
306			{
307	root	1.4	sanitise_stdfd ();
308
309	root	1.1	uid_t uid = getuid ();
310			gid_t gid = getgid ();
311	ayin	1.6
312	root	1.1	// before doing anything else, check for setuid/setgid operation,
313			// start the helper process and drop privileges
314			if (uid != geteuid ()
315			\|\| gid != getegid ())
316			{
317			#if PTYTTY_HELPER
318			use_helper ();
319			#else
320	sf-exg	1.17	PTYTTY_WARN ("running setuid/setgid without pty helper compiled in, continuing unprivileged.\n");
321	root	1.1	#endif
322
323			drop_privileges ();
324			}
325			}
326
327			void
328			ptytty::drop_privileges ()
329			{
330			uid_t uid = getuid ();
331			gid_t gid = getgid ();
332
333			// drop privileges
334			#if HAVE_SETRESUID
335			setresgid (gid, gid, gid);
336			setresuid (uid, uid, uid);
337			#elif HAVE_SETREUID
338			setregid (gid, gid);
339			setreuid (uid, uid);
340			#elif HAVE_SETUID
341			setgid (gid);
342			setuid (uid);
343			#else
344			# error no way to drop privileges, configure failed?
345			#endif
346
347			if (uid != geteuid ()
348			\|\| gid != getegid ())
349	sf-exg	1.10	PTYTTY_FATAL ("unable to drop privileges, aborting.\n");
350	root	1.1	}
351