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
{
private:

  ptytty *id;

public:

  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))
    throw ptytty_error ("protocol error while creating pty using helper process.\n");

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

  if ((pty = recv_fd (sock_fd)) < 0
      || (tty = recv_fd (sock_fd)) < 0)
    throw ptytty_error ("protocol error while reading pty/tty fds from helper process.\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))
    throw ptytty_error ("could not create socket to communicate with pty/sessiondb helper.\n");

#if PTYTTY_REENTRANT
  int lv[2];

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

  helper_pid = fork ();

  if (helper_pid < 0)
    throw ptytty_error ("could not create pty/sessiondb helper process.\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)
          throw ptytty_error ("unable to sanitise fds.\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 ();
#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 ())
    throw ptytty_error ("unable to drop privileges.\n");
}

Revision:	1.27
Committed:	Sat Jun 26 14:31:15 2021 UTC (5 years, 2 months ago) by sf-exg
Content type:	text/plain
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.26:	+7 -9 lines
Log Message:	Remove PTYTTY_{WARN,FATAL} and throw on failure
#	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	sf-exg	1.26	private:
60
61	root	1.1	ptytty *id;
62
63	sf-exg	1.26	public:
64
65	root	1.1	ptytty_proxy ()
66			: id(0)
67			{
68			}
69
70			~ptytty_proxy ();
71
72			bool get ();
73			void login (int cmd_pid, bool login_shell, const char *hostname);
74			};
75
76			#if PTYTTY_REENTRANT
77	root	1.23	# define NEED_TOKEN do { char ch; read (lock_fd, &ch , 1); } while (0)
78			# define GIVE_TOKEN write (lock_fd, &lock_fd, 1)
79	root	1.1	#else
80			# define NEED_TOKEN (void)0
81			# define GIVE_TOKEN (void)0
82			#endif
83
84			bool
85			ptytty_proxy::get ()
86			{
87			NEED_TOKEN;
88
89			command cmd;
90
91			cmd.type = command::get;
92
93			write (sock_fd, &cmd, sizeof (cmd));
94
95			if (read (sock_fd, &id, sizeof (id)) != sizeof (id))
96	sf-exg	1.27	throw ptytty_error ("protocol error while creating pty using helper process.\n");
97	root	1.1
98			if (!id)
99			{
100			GIVE_TOKEN;
101			return false;
102			}
103
104			if ((pty = recv_fd (sock_fd)) < 0
105			\|\| (tty = recv_fd (sock_fd)) < 0)
106	sf-exg	1.27	throw ptytty_error ("protocol error while reading pty/tty fds from helper process.\n");
107	root	1.1
108			GIVE_TOKEN;
109			return true;
110			}
111
112			void
113			ptytty_proxy::login (int cmd_pid, bool login_shell, const char *hostname)
114			{
115			NEED_TOKEN;
116
117			command cmd;
118
119			cmd.type = command::login;
120			cmd.id = id;
121			cmd.cmd_pid = cmd_pid;
122			cmd.login_shell = login_shell;
123			strncpy (cmd.hostname, hostname, sizeof (cmd.hostname));
124
125			write (sock_fd, &cmd, sizeof (cmd));
126
127			GIVE_TOKEN;
128			}
129
130			ptytty_proxy::~ptytty_proxy ()
131			{
132			if (id)
133			{
134	ayin	1.3	close_tty ();
135
136			if (pty >= 0)
137			close (pty);
138	ayin	1.2
139	root	1.1	NEED_TOKEN;
140
141			command cmd;
142
143			cmd.type = command::destroy;
144			cmd.id = id;
145
146			write (sock_fd, &cmd, sizeof (cmd));
147
148			GIVE_TOKEN;
149			}
150			}
151
152	sf-exg	1.25	static void
153			serve ()
154	root	1.1	{
155			command cmd;
156			vector<ptytty *> ptys;
157
158			for (;;)
159			{
160			GIVE_TOKEN;
161
162			if (read (sock_fd, &cmd, sizeof (command)) != sizeof (command))
163			break;
164
165			if (cmd.type == command::get)
166			{
167			// -> id ptyfd ttyfd
168			cmd.id = new ptytty_unix;
169
170			if (cmd.id->get ())
171			{
172			write (sock_fd, &cmd.id, sizeof (cmd.id));
173			ptys.push_back (cmd.id);
174
175			ptytty::send_fd (sock_fd, cmd.id->pty);
176			ptytty::send_fd (sock_fd, cmd.id->tty);
177	sf-exg	1.21
178			cmd.id->close_tty ();
179	root	1.1	}
180			else
181			{
182			delete cmd.id;
183			cmd.id = 0;
184			write (sock_fd, &cmd.id, sizeof (cmd.id));
185			}
186			}
187			else if (cmd.type == command::login)
188			{
189			#if UTMP_SUPPORT
190			if (find (ptys.begin (), ptys.end (), cmd.id) != ptys.end ())
191			{
192			cmd.hostname[sizeof (cmd.hostname) - 1] = 0;
193			cmd.id->login (cmd.cmd_pid, cmd.login_shell, cmd.hostname);
194			}
195			#endif
196			}
197			else if (cmd.type == command::destroy)
198			{
199			vector<ptytty *>::iterator pty = find (ptys.begin (), ptys.end (), cmd.id);
200
201			if (pty != ptys.end ())
202			{
203			delete *pty;
204			ptys.erase (pty);
205			}
206			}
207			else
208			break;
209
210			NEED_TOKEN;
211			}
212
213			// destroy all ptys
214			for (vector<ptytty *>::iterator i = ptys.end (); i-- > ptys.begin (); )
215			delete *i;
216			}
217
218			void
219			ptytty::use_helper ()
220			{
221	root	1.18	if (sock_fd >= 0)
222	root	1.1	return;
223
224			int sv[2];
225
226			if (socketpair (AF_UNIX, SOCK_STREAM, 0, sv))
227	sf-exg	1.27	throw ptytty_error ("could not create socket to communicate with pty/sessiondb helper.\n");
228	root	1.1
229	sf-exg	1.12	#if PTYTTY_REENTRANT
230	root	1.1	int lv[2];
231
232			if (socketpair (AF_UNIX, SOCK_STREAM, 0, lv))
233	sf-exg	1.27	throw ptytty_error ("could not create socket to communicate with pty/sessiondb helper.\n");
234	root	1.1	#endif
235
236			helper_pid = fork ();
237
238			if (helper_pid < 0)
239	sf-exg	1.27	throw ptytty_error ("could not create pty/sessiondb helper process.\n");
240	root	1.1
241			if (helper_pid)
242			{
243			// client, process
244			sock_fd = sv[0];
245			close (sv[1]);
246			fcntl (sock_fd, F_SETFD, FD_CLOEXEC);
247	sf-exg	1.12	#if PTYTTY_REENTRANT
248	root	1.1	lock_fd = lv[0];
249			close (lv[1]);
250			fcntl (lock_fd, F_SETFD, FD_CLOEXEC);
251			#endif
252			}
253			else
254			{
255			// server, pty-helper
256			sock_fd = sv[1];
257	sf-exg	1.12	#if PTYTTY_REENTRANT
258	root	1.1	lock_fd = lv[1];
259			#endif
260
261			chdir ("/");
262
263			signal (SIGHUP, SIG_IGN);
264			signal (SIGTERM, SIG_IGN);
265			signal (SIGINT, SIG_IGN);
266			signal (SIGPIPE, SIG_IGN);
267
268			for (int fd = 0; fd < 1023; fd++)
269			if (fd != sock_fd && fd != lock_fd)
270			close (fd);
271
272			serve ();
273			_exit (EXIT_SUCCESS);
274			}
275			}
276
277			#endif
278
279			ptytty *
280			ptytty::create ()
281			{
282			#if PTYTTY_HELPER
283	root	1.18	if (helper_pid)
284	root	1.1	// use helper process
285			return new ptytty_proxy;
286			else
287			#endif
288			return new ptytty_unix;
289			}
290
291			void
292	root	1.4	ptytty::sanitise_stdfd ()
293			{
294			// sanitise stdin/stdout/stderr to point to something.
295			for (int fd = 0; fd <= 2; ++fd)
296			if (fcntl (fd, F_GETFL) < 0 && errno == EBADF)
297			{
298			int fd2 = open ("/dev/tty", fd ? O_WRONLY : O_RDONLY);
299
300			if (fd2 < 0)
301	root	1.5	fd2 = open ("/dev/null", fd ? O_WRONLY : O_RDONLY);
302	root	1.4
303			if (fd2 != fd)
304	sf-exg	1.27	throw ptytty_error ("unable to sanitise fds.\n");
305	root	1.4	}
306			}
307
308			void
309	root	1.1	ptytty::init ()
310			{
311	root	1.4	sanitise_stdfd ();
312
313	root	1.1	uid_t uid = getuid ();
314			gid_t gid = getgid ();
315	ayin	1.6
316	root	1.1	// before doing anything else, check for setuid/setgid operation,
317			// start the helper process and drop privileges
318			if (uid != geteuid ()
319			\|\| gid != getegid ())
320			{
321			#if PTYTTY_HELPER
322			use_helper ();
323			#endif
324
325			drop_privileges ();
326			}
327			}
328
329			void
330			ptytty::drop_privileges ()
331			{
332			uid_t uid = getuid ();
333			gid_t gid = getgid ();
334
335			// drop privileges
336			#if HAVE_SETRESUID
337			setresgid (gid, gid, gid);
338			setresuid (uid, uid, uid);
339			#elif HAVE_SETREUID
340			setregid (gid, gid);
341			setreuid (uid, uid);
342			#elif HAVE_SETUID
343			setgid (gid);
344			setuid (uid);
345			#else
346			# error no way to drop privileges, configure failed?
347			#endif
348
349			if (uid != geteuid ()
350			\|\| gid != getegid ())
351	sf-exg	1.27	throw ptytty_error ("unable to drop privileges.\n");
352	root	1.1	}
353