propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 2af95f00ebd5bb7a28b3817db1218442c935388e)

            to branch 'au.asn.ucc.matt.dropbear' (head ecd779509ef23a8cdf64888904fc9b31d78aa933)

--HG--
extra : convert_revision : d26d5eb2837f46b56a33fb0e7573aa0201abd4d5

1 files changed, 1014 insertions, 0 deletions

diff --git a/svr-chansession.c b/svr-chansession.c
new file mode 100644
index 0000000..19c4f4a
--- /dev/null
+++ b/svr-chansession.c
@@ -0,0 +1,1014 @@
+/*
+ * Dropbear - a SSH2 server
+ * 
+ * Copyright (c) 2002,2003 Matt Johnston
+ * All rights reserved.
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE. */
+
+#include "includes.h"
+#include "packet.h"
+#include "buffer.h"
+#include "session.h"
+#include "dbutil.h"
+#include "channel.h"
+#include "chansession.h"
+#include "sshpty.h"
+#include "termcodes.h"
+#include "ssh.h"
+#include "random.h"
+#include "utmp.h"
+#include "x11fwd.h"
+#include "agentfwd.h"
+#include "runopts.h"
+
+/* Handles sessions (either shells or programs) requested by the client */
+
+static int sessioncommand(struct Channel *channel, struct ChanSess *chansess,
+		int iscmd, int issubsys);
+static int sessionpty(struct ChanSess * chansess);
+static int sessionsignal(struct ChanSess *chansess);
+static int noptycommand(struct Channel *channel, struct ChanSess *chansess);
+static int ptycommand(struct Channel *channel, struct ChanSess *chansess);
+static int sessionwinchange(struct ChanSess *chansess);
+static void execchild(struct ChanSess *chansess);
+static void addchildpid(struct ChanSess *chansess, pid_t pid);
+static void sesssigchild_handler(int val);
+static void closechansess(struct Channel *channel);
+static int newchansess(struct Channel *channel);
+static void chansessionrequest(struct Channel *channel);
+
+static void send_exitsignalstatus(struct Channel *channel);
+static void send_msg_chansess_exitstatus(struct Channel * channel,
+		struct ChanSess * chansess);
+static void send_msg_chansess_exitsignal(struct Channel * channel,
+		struct ChanSess * chansess);
+static int sesscheckclose(struct Channel *channel);
+static void get_termmodes(struct ChanSess *chansess);
+
+
+/* required to clear environment */
+extern char** environ;
+
+static int sesscheckclose(struct Channel *channel) {
+	return channel->writefd == -1;
+}
+
+/* Handler for childs exiting, store the state for return to the client */
+
+/* There's a particular race we have to watch out for: if the forked child
+ * executes, exits, and this signal-handler is called, all before the parent
+ * gets to run, then the childpids[] array won't have the pid in it. Hence we
+ * use the svr_ses.lastexit struct to hold the exit, which is then compared by
+ * the parent when it runs. This work correctly at least in the case of a
+ * single shell spawned (ie the usual case) */
+static void sesssigchild_handler(int UNUSED(dummy)) {
+
+	int status;
+	pid_t pid;
+	unsigned int i;
+	struct sigaction sa_chld;
+	struct exitinfo *exit = NULL;
+
+	TRACE(("enter sigchld handler"))
+	while ((pid = waitpid(-1, &status, WNOHANG)) > 0) {
+
+		exit = NULL;
+		/* find the corresponding chansess */
+		for (i = 0; i < svr_ses.childpidsize; i++) {
+			if (svr_ses.childpids[i].pid == pid) {
+
+				exit = &svr_ses.childpids[i].chansess->exit;
+				break;
+			}
+		}
+
+		/* If the pid wasn't matched, then we might have hit the race mentioned
+		 * above. So we just store the info for the parent to deal with */
+		if (exit == NULL) {
+			exit = &svr_ses.lastexit;
+		}
+
+		exit->exitpid = pid;
+		if (WIFEXITED(status)) {
+			exit->exitstatus = WEXITSTATUS(status);
+		}
+		if (WIFSIGNALED(status)) {
+			exit->exitsignal = WTERMSIG(status);
+#if !defined(AIX) && defined(WCOREDUMP)
+			exit->exitcore = WCOREDUMP(status);
+#else
+			exit->exitcore = 0;
+#endif
+		} else {
+			/* we use this to determine how pid exited */
+			exit->exitsignal = -1;
+		}
+	}
+
+	
+	sa_chld.sa_handler = sesssigchild_handler;
+	sa_chld.sa_flags = SA_NOCLDSTOP;
+	sigaction(SIGCHLD, &sa_chld, NULL);
+	TRACE(("leave sigchld handler"))
+}
+
+/* send the exit status or the signal causing termination for a session */
+/* XXX server */
+static void send_exitsignalstatus(struct Channel *channel) {
+
+	struct ChanSess *chansess = (struct ChanSess*)channel->typedata;
+
+	if (chansess->exit.exitpid >= 0) {
+		if (chansess->exit.exitsignal > 0) {
+			send_msg_chansess_exitsignal(channel, chansess);
+		} else {
+			send_msg_chansess_exitstatus(channel, chansess);
+		}
+	}
+}
+
+/* send the exitstatus to the client */
+static void send_msg_chansess_exitstatus(struct Channel * channel,
+		struct ChanSess * chansess) {
+
+	dropbear_assert(chansess->exit.exitpid != -1);
+	dropbear_assert(chansess->exit.exitsignal == -1);
+
+	CHECKCLEARTOWRITE();
+
+	buf_putbyte(ses.writepayload, SSH_MSG_CHANNEL_REQUEST);
+	buf_putint(ses.writepayload, channel->remotechan);
+	buf_putstring(ses.writepayload, "exit-status", 11);
+	buf_putbyte(ses.writepayload, 0); /* boolean FALSE */
+	buf_putint(ses.writepayload, chansess->exit.exitstatus);
+
+	encrypt_packet();
+
+}
+
+/* send the signal causing the exit to the client */
+static void send_msg_chansess_exitsignal(struct Channel * channel,
+		struct ChanSess * chansess) {
+
+	int i;
+	char* signame = NULL;
+
+	dropbear_assert(chansess->exit.exitpid != -1);
+	dropbear_assert(chansess->exit.exitsignal > 0);
+
+	CHECKCLEARTOWRITE();
+
+	/* we check that we can match a signal name, otherwise
+	 * don't send anything */
+	for (i = 0; signames[i].name != NULL; i++) {
+		if (signames[i].signal == chansess->exit.exitsignal) {
+			signame = signames[i].name;
+			break;
+		}
+	}
+
+	if (signame == NULL) {
+		return;
+	}
+
+	buf_putbyte(ses.writepayload, SSH_MSG_CHANNEL_REQUEST);
+	buf_putint(ses.writepayload, channel->remotechan);
+	buf_putstring(ses.writepayload, "exit-signal", 11);
+	buf_putbyte(ses.writepayload, 0); /* boolean FALSE */
+	buf_putstring(ses.writepayload, signame, strlen(signame));
+	buf_putbyte(ses.writepayload, chansess->exit.exitcore);
+	buf_putstring(ses.writepayload, "", 0); /* error msg */
+	buf_putstring(ses.writepayload, "", 0); /* lang */
+
+	encrypt_packet();
+}
+
+/* set up a session channel */
+static int newchansess(struct Channel *channel) {
+
+	struct ChanSess *chansess;
+
+	dropbear_assert(channel->typedata == NULL);
+
+	chansess = (struct ChanSess*)m_malloc(sizeof(struct ChanSess));
+	chansess->cmd = NULL;
+	chansess->pid = 0;
+
+	/* pty details */
+	chansess->master = -1;
+	chansess->slave = -1;
+	chansess->tty = NULL;
+	chansess->term = NULL;
+
+	chansess->exit.exitpid = -1;
+
+	channel->typedata = chansess;
+
+#ifndef DISABLE_X11FWD
+	chansess->x11listener = NULL;
+	chansess->x11authprot = NULL;
+	chansess->x11authcookie = NULL;
+#endif
+
+#ifndef DISABLE_AGENTFWD
+	chansess->agentlistener = NULL;
+	chansess->agentfile = NULL;
+	chansess->agentdir = NULL;
+#endif
+
+	return 0;
+
+}
+
+/* clean a session channel */
+static void closechansess(struct Channel *channel) {
+
+	struct ChanSess *chansess;
+	unsigned int i;
+	struct logininfo *li;
+
+	chansess = (struct ChanSess*)channel->typedata;
+
+	send_exitsignalstatus(channel);
+
+	TRACE(("enter closechansess"))
+	if (chansess == NULL) {
+		TRACE(("leave closechansess: chansess == NULL"))
+		return;
+	}
+
+	m_free(chansess->cmd);
+	m_free(chansess->term);
+
+	if (chansess->tty) {
+		/* write the utmp/wtmp login record */
+		li = login_alloc_entry(chansess->pid, ses.authstate.username,
+				ses.remotehost, chansess->tty);
+		login_logout(li);
+		login_free_entry(li);
+
+		pty_release(chansess->tty);
+		m_free(chansess->tty);
+	}
+
+#ifndef DISABLE_X11FWD
+	x11cleanup(chansess);
+#endif
+
+#ifndef DISABLE_AGENTFWD
+	agentcleanup(chansess);
+#endif
+
+	/* clear child pid entries */
+	for (i = 0; i < svr_ses.childpidsize; i++) {
+		if (svr_ses.childpids[i].chansess == chansess) {
+			dropbear_assert(svr_ses.childpids[i].pid > 0);
+			TRACE(("closing pid %d", svr_ses.childpids[i].pid))
+			TRACE(("exitpid = %d", chansess->exit.exitpid))
+			svr_ses.childpids[i].pid = -1;
+			svr_ses.childpids[i].chansess = NULL;
+		}
+	}
+				
+	m_free(chansess);
+
+	TRACE(("leave closechansess"))
+}
+
+/* Handle requests for a channel. These can be execution requests,
+ * or x11/authagent forwarding. These are passed to appropriate handlers */
+static void chansessionrequest(struct Channel *channel) {
+
+	unsigned char * type = NULL;
+	unsigned int typelen;
+	unsigned char wantreply;
+	int ret = 1;
+	struct ChanSess *chansess;
+
+	TRACE(("enter chansessionrequest"))
+
+	type = buf_getstring(ses.payload, &typelen);
+	wantreply = buf_getbool(ses.payload);
+
+	if (typelen > MAX_NAME_LEN) {
+		TRACE(("leave chansessionrequest: type too long")) /* XXX send error?*/
+		goto out;
+	}
+
+	chansess = (struct ChanSess*)channel->typedata;
+	dropbear_assert(chansess != NULL);
+	TRACE(("type is %s", type))
+
+	if (strcmp(type, "window-change") == 0) {
+		ret = sessionwinchange(chansess);
+	} else if (strcmp(type, "shell") == 0) {
+		ret = sessioncommand(channel, chansess, 0, 0);
+	} else if (strcmp(type, "pty-req") == 0) {
+		ret = sessionpty(chansess);
+	} else if (strcmp(type, "exec") == 0) {
+		ret = sessioncommand(channel, chansess, 1, 0);
+	} else if (strcmp(type, "subsystem") == 0) {
+		ret = sessioncommand(channel, chansess, 1, 1);
+#ifndef DISABLE_X11FWD
+	} else if (strcmp(type, "x11-req") == 0) {
+		ret = x11req(chansess);
+#endif
+#ifndef DISABLE_AGENTFWD
+	} else if (strcmp(type, "auth-agent-req@openssh.com") == 0) {
+		ret = agentreq(chansess);
+#endif
+	} else if (strcmp(type, "signal") == 0) {
+		ret = sessionsignal(chansess);
+	} else {
+		/* etc, todo "env", "subsystem" */
+	}
+
+out:
+
+	if (wantreply) {
+		if (ret == DROPBEAR_SUCCESS) {
+			send_msg_channel_success(channel);
+		} else {
+			send_msg_channel_failure(channel);
+		}
+	}
+
+	m_free(type);
+	TRACE(("leave chansessionrequest"))
+}
+
+
+/* Send a signal to a session's process as requested by the client*/
+static int sessionsignal(struct ChanSess *chansess) {
+
+	int sig = 0;
+	unsigned char* signame = NULL;
+	int i;
+
+	if (chansess->pid == 0) {
+		/* haven't got a process pid yet */
+		return DROPBEAR_FAILURE;
+	}
+
+	signame = buf_getstring(ses.payload, NULL);
+
+	i = 0;
+	while (signames[i].name != 0) {
+		if (strcmp(signames[i].name, signame) == 0) {
+			sig = signames[i].signal;
+			break;
+		}
+		i++;
+	}
+
+	m_free(signame);
+
+	if (sig == 0) {
+		/* failed */
+		return DROPBEAR_FAILURE;
+	}
+			
+	if (kill(chansess->pid, sig) < 0) {
+		return DROPBEAR_FAILURE;
+	} 
+
+	return DROPBEAR_SUCCESS;
+}
+
+/* Let the process know that the window size has changed, as notified from the
+ * client. Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
+static int sessionwinchange(struct ChanSess *chansess) {
+
+	int termc, termr, termw, termh;
+
+	if (chansess->master < 0) {
+		/* haven't got a pty yet */
+		return DROPBEAR_FAILURE;
+	}
+			
+	termc = buf_getint(ses.payload);
+	termr = buf_getint(ses.payload);
+	termw = buf_getint(ses.payload);
+	termh = buf_getint(ses.payload);
+	
+	pty_change_window_size(chansess->master, termr, termc, termw, termh);
+
+	return DROPBEAR_SUCCESS;
+}
+
+static void get_termmodes(struct ChanSess *chansess) {
+
+	struct termios termio;
+	unsigned char opcode;
+	unsigned int value;
+	const struct TermCode * termcode;
+	unsigned int len;
+
+	TRACE(("enter get_termmodes"))
+
+	/* Term modes */
+	/* We'll ignore errors and continue if we can't set modes.
+	 * We're ignoring baud rates since they seem evil */
+	if (tcgetattr(chansess->master, &termio) == -1) {
+		return;
+	}
+
+	len = buf_getint(ses.payload);
+	TRACE(("term mode str %d p->l %d p->p %d", 
+				len, ses.payload->len , ses.payload->pos));
+	if (len != ses.payload->len - ses.payload->pos) {
+		dropbear_exit("bad term mode string");
+	}
+
+	if (len == 0) {
+		TRACE(("leave get_termmodes: empty terminal modes string"))
+		return;
+	}
+
+	while (((opcode = buf_getbyte(ses.payload)) != 0x00) && opcode <= 159) {
+
+		/* must be before checking type, so that value is consumed even if
+		 * we don't use it */
+		value = buf_getint(ses.payload);
+
+		/* handle types of code */
+		if (opcode > MAX_TERMCODE) {
+			continue;
+		}
+		termcode = &termcodes[(unsigned int)opcode];
+		
+
+		switch (termcode->type) {
+
+			case TERMCODE_NONE:
+				break;
+
+			case TERMCODE_CONTROLCHAR:
+				termio.c_cc[termcode->mapcode] = value;
+				break;
+
+			case TERMCODE_INPUT:
+				if (value) {
+					termio.c_iflag |= termcode->mapcode;
+				} else {
+					termio.c_iflag &= ~(termcode->mapcode);
+				}
+				break;
+
+			case TERMCODE_OUTPUT:
+				if (value) {
+					termio.c_oflag |= termcode->mapcode;
+				} else {
+					termio.c_oflag &= ~(termcode->mapcode);
+				}
+				break;
+
+			case TERMCODE_LOCAL:
+				if (value) {
+					termio.c_lflag |= termcode->mapcode;
+				} else {
+					termio.c_lflag &= ~(termcode->mapcode);
+				}
+				break;
+
+			case TERMCODE_CONTROL:
+				if (value) {
+					termio.c_cflag |= termcode->mapcode;
+				} else {
+					termio.c_cflag &= ~(termcode->mapcode);
+				}
+				break;
+				
+		}
+	}
+	if (tcsetattr(chansess->master, TCSANOW, &termio) < 0) {
+		dropbear_log(LOG_INFO, "error setting terminal attributes");
+	}
+	TRACE(("leave get_termmodes"))
+}
+
+/* Set up a session pty which will be used to execute the shell or program.
+ * The pty is allocated now, and kept for when the shell/program executes.
+ * Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
+static int sessionpty(struct ChanSess * chansess) {
+
+	unsigned int termlen;
+	unsigned char namebuf[65];
+
+	TRACE(("enter sessionpty"))
+	chansess->term = buf_getstring(ses.payload, &termlen);
+	if (termlen > MAX_TERM_LEN) {
+		/* TODO send disconnect ? */
+		TRACE(("leave sessionpty: term len too long"))
+		return DROPBEAR_FAILURE;
+	}
+
+	/* allocate the pty */
+	if (chansess->master != -1) {
+		dropbear_exit("multiple pty requests");
+	}
+	if (pty_allocate(&chansess->master, &chansess->slave, namebuf, 64) == 0) {
+		TRACE(("leave sessionpty: failed to allocate pty"))
+		return DROPBEAR_FAILURE;
+	}
+	
+	chansess->tty = (char*)m_strdup(namebuf);
+	if (!chansess->tty) {
+		dropbear_exit("out of memory"); /* TODO disconnect */
+	}
+
+	pty_setowner(ses.authstate.pw, chansess->tty);
+
+	/* Set up the rows/col counts */
+	sessionwinchange(chansess);
+
+	/* Read the terminal modes */
+	get_termmodes(chansess);
+
+	TRACE(("leave sessionpty"))
+	return DROPBEAR_SUCCESS;
+}
+
+/* Handle a command request from the client. This is used for both shell
+ * and command-execution requests, and passes the command to
+ * noptycommand or ptycommand as appropriate.
+ * Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
+static int sessioncommand(struct Channel *channel, struct ChanSess *chansess,
+		int iscmd, int issubsys) {
+
+	unsigned int cmdlen;
+	int ret;
+
+	TRACE(("enter sessioncommand"))
+
+	if (chansess->cmd != NULL) {
+		/* Note that only one command can _succeed_. The client might try
+		 * one command (which fails), then try another. Ie fallback
+		 * from sftp to scp */
+		return DROPBEAR_FAILURE;
+	}
+
+	if (iscmd) {
+		/* "exec" */
+		chansess->cmd = buf_getstring(ses.payload, &cmdlen);
+
+		if (cmdlen > MAX_CMD_LEN) {
+			m_free(chansess->cmd);
+			/* TODO - send error - too long ? */
+			return DROPBEAR_FAILURE;
+		}
+		if (issubsys) {
+#ifdef SFTPSERVER_PATH
+			if ((cmdlen == 4) && strncmp(chansess->cmd, "sftp", 4) == 0) {
+				m_free(chansess->cmd);
+				chansess->cmd = m_strdup(SFTPSERVER_PATH);
+			} else 
+#endif
+			{
+				m_free(chansess->cmd);
+				return DROPBEAR_FAILURE;
+			}
+		}
+	}
+
+#ifdef LOG_COMMANDS
+	if (chansess->cmd) {
+		dropbear_log(LOG_INFO, "user %s executing '%s'", 
+						ses.authstate.printableuser, chansess->cmd);
+	} else {
+		dropbear_log(LOG_INFO, "user %s executing login shell", 
+						ses.authstate.printableuser);
+	}
+#endif
+
+	if (chansess->term == NULL) {
+		/* no pty */
+		ret = noptycommand(channel, chansess);
+	} else {
+		/* want pty */
+		ret = ptycommand(channel, chansess);
+	}
+
+	if (ret == DROPBEAR_FAILURE) {
+		m_free(chansess->cmd);
+	}
+	return ret;
+}
+
+/* Execute a command and set up redirection of stdin/stdout/stderr without a
+ * pty.
+ * Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
+static int noptycommand(struct Channel *channel, struct ChanSess *chansess) {
+
+	int infds[2];
+	int outfds[2];
+	int errfds[2];
+	pid_t pid;
+	unsigned int i;
+
+	TRACE(("enter noptycommand"))
+
+	/* redirect stdin/stdout/stderr */
+	if (pipe(infds) != 0)
+		return DROPBEAR_FAILURE;
+	if (pipe(outfds) != 0)
+		return DROPBEAR_FAILURE;
+	if (pipe(errfds) != 0)
+		return DROPBEAR_FAILURE;
+
+#ifdef __uClinux__
+	pid = vfork();
+#else
+	pid = fork();
+#endif
+
+	if (pid < 0)
+		return DROPBEAR_FAILURE;
+
+	if (!pid) {
+		/* child */
+
+		/* redirect stdin/stdout */
+#define FDIN 0
+#define FDOUT 1
+		if ((dup2(infds[FDIN], STDIN_FILENO) < 0) ||
+			(dup2(outfds[FDOUT], STDOUT_FILENO) < 0) ||
+			(dup2(errfds[FDOUT], STDERR_FILENO) < 0)) {
+			TRACE(("leave noptycommand: error redirecting FDs"))
+			return DROPBEAR_FAILURE;
+		}
+
+		close(infds[FDOUT]);
+		close(infds[FDIN]);
+		close(outfds[FDIN]);
+		close(outfds[FDOUT]);
+		close(errfds[FDIN]);
+		close(errfds[FDOUT]);
+
+		execchild(chansess);
+		/* not reached */
+
+	} else {
+		/* parent */
+		TRACE(("continue noptycommand: parent"))
+		chansess->pid = pid;
+
+		addchildpid(chansess, pid);
+
+		if (svr_ses.lastexit.exitpid != -1) {
+			/* The child probably exited and the signal handler triggered
+			 * possibly before we got around to adding the childpid. So we fill
+			 * out it's data manually */
+			for (i = 0; i < svr_ses.childpidsize; i++) {
+				if (svr_ses.childpids[i].pid == pid) {
+					svr_ses.childpids[i].chansess->exit = svr_ses.lastexit;
+					svr_ses.lastexit.exitpid = -1;
+				}
+			}
+		}
+
+
+		close(infds[FDIN]);
+		close(outfds[FDOUT]);
+		close(errfds[FDOUT]);
+		channel->writefd = infds[FDOUT];
+		channel->readfd = outfds[FDIN];
+		channel->errfd = errfds[FDIN];
+		ses.maxfd = MAX(ses.maxfd, channel->writefd);
+		ses.maxfd = MAX(ses.maxfd, channel->readfd);
+		ses.maxfd = MAX(ses.maxfd, channel->errfd);
+
+		setnonblocking(channel->readfd);
+		setnonblocking(channel->writefd);
+		setnonblocking(channel->errfd);
+
+	}
+#undef FDIN
+#undef FDOUT
+
+	TRACE(("leave noptycommand"))
+	return DROPBEAR_SUCCESS;
+}
+
+/* Execute a command or shell within a pty environment, and set up
+ * redirection as appropriate.
+ * Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
+static int ptycommand(struct Channel *channel, struct ChanSess *chansess) {
+
+	pid_t pid;
+	struct logininfo *li = NULL;
+#ifdef DO_MOTD
+	buffer * motdbuf = NULL;
+	int len;
+	struct stat sb;
+	char *hushpath = NULL;
+#endif
+
+	TRACE(("enter ptycommand"))
+
+	/* we need to have a pty allocated */
+	if (chansess->master == -1 || chansess->tty == NULL) {
+		dropbear_log(LOG_WARNING, "no pty was allocated, couldn't execute");
+		return DROPBEAR_FAILURE;
+	}
+	
+#ifdef __uClinux__
+	pid = vfork();
+#else
+	pid = fork();
+#endif
+	if (pid < 0)
+		return DROPBEAR_FAILURE;
+
+	if (pid == 0) {
+		/* child */
+		
+		/* redirect stdin/stdout/stderr */
+		close(chansess->master);
+
+		pty_make_controlling_tty(&chansess->slave, chansess->tty);
+		
+		if ((dup2(chansess->slave, STDIN_FILENO) < 0) ||
+			(dup2(chansess->slave, STDERR_FILENO) < 0) ||
+			(dup2(chansess->slave, STDOUT_FILENO) < 0)) {
+			TRACE(("leave ptycommand: error redirecting filedesc"))
+			return DROPBEAR_FAILURE;
+		}
+
+		close(chansess->slave);
+
+		/* write the utmp/wtmp login record - must be after changing the
+		 * terminal used for stdout with the dup2 above */
+		li= login_alloc_entry(getpid(), ses.authstate.username,
+				ses.remotehost, chansess->tty);
+		login_login(li);
+		login_free_entry(li);
+
+		m_free(chansess->tty);
+
+#ifdef DO_MOTD
+		if (svr_opts.domotd) {
+			/* don't show the motd if ~/.hushlogin exists */
+
+			/* 11 == strlen("/hushlogin\0") */
+			len = strlen(ses.authstate.pw->pw_dir) + 11; 
+
+			hushpath = m_malloc(len);
+			snprintf(hushpath, len, "%s/hushlogin", ses.authstate.pw->pw_dir);
+
+			if (stat(hushpath, &sb) < 0) {
+				/* more than a screenful is stupid IMHO */
+				motdbuf = buf_new(80 * 25);
+				if (buf_readfile(motdbuf, MOTD_FILENAME) == DROPBEAR_SUCCESS) {
+					buf_setpos(motdbuf, 0);
+					while (motdbuf->pos != motdbuf->len) {
+						len = motdbuf->len - motdbuf->pos;
+						len = write(STDOUT_FILENO, 
+								buf_getptr(motdbuf, len), len);
+						buf_incrpos(motdbuf, len);
+					}
+				}
+				buf_free(motdbuf);
+			}
+			m_free(hushpath);
+		}
+#endif /* DO_MOTD */
+
+		execchild(chansess);
+		/* not reached */
+
+	} else {
+		/* parent */
+		TRACE(("continue ptycommand: parent"))
+		chansess->pid = pid;
+
+		/* add a child pid */
+		addchildpid(chansess, pid);
+
+		close(chansess->slave);
+		channel->writefd = chansess->master;
+		channel->readfd = chansess->master;
+		/* don't need to set stderr here */
+		ses.maxfd = MAX(ses.maxfd, chansess->master);
+
+		setnonblocking(chansess->master);
+
+	}
+
+	TRACE(("leave ptycommand"))
+	return DROPBEAR_SUCCESS;
+}
+
+/* Add the pid of a child to the list for exit-handling */
+static void addchildpid(struct ChanSess *chansess, pid_t pid) {
+
+	unsigned int i;
+	for (i = 0; i < svr_ses.childpidsize; i++) {
+		if (svr_ses.childpids[i].pid == -1) {
+			break;
+		}
+	}
+
+	/* need to increase size */
+	if (i == svr_ses.childpidsize) {
+		svr_ses.childpids = (struct ChildPid*)m_realloc(svr_ses.childpids,
+				sizeof(struct ChildPid) * (svr_ses.childpidsize+1));
+		svr_ses.childpidsize++;
+	}
+	
+	svr_ses.childpids[i].pid = pid;
+	svr_ses.childpids[i].chansess = chansess;
+
+}
+
+/* Clean up, drop to user privileges, set up the environment and execute
+ * the command/shell. This function does not return. */
+static void execchild(struct ChanSess *chansess) {
+
+	char *argv[4];
+	char * usershell = NULL;
+	char * baseshell = NULL;
+	unsigned int i;
+
+    /* with uClinux we'll have vfork()ed, so don't want to overwrite the
+     * hostkey. can't think of a workaround to clear it */
+#ifndef __uClinux__
+	/* wipe the hostkey */
+	sign_key_free(svr_opts.hostkey);
+	svr_opts.hostkey = NULL;
+
+	/* overwrite the prng state */
+	reseedrandom();
+#endif
+
+	/* close file descriptors except stdin/stdout/stderr
+	 * Need to be sure FDs are closed here to avoid reading files as root */
+	for (i = 3; i <= (unsigned int)ses.maxfd; i++) {
+		m_close(i);
+	}
+
+	/* clear environment */
+	/* if we're debugging using valgrind etc, we need to keep the LD_PRELOAD
+	 * etc. This is hazardous, so should only be used for debugging. */
+#ifndef DEBUG_VALGRIND
+#ifdef HAVE_CLEARENV
+	clearenv();
+#else /* don't HAVE_CLEARENV */
+	/* Yay for posix. */
+	if (environ) {
+		environ[0] = NULL;
+	}
+#endif /* HAVE_CLEARENV */
+#endif /* DEBUG_VALGRIND */
+
+	/* We can only change uid/gid as root ... */
+	if (getuid() == 0) {
+
+		if ((setgid(ses.authstate.pw->pw_gid) < 0) ||
+			(initgroups(ses.authstate.pw->pw_name, 
+						ses.authstate.pw->pw_gid) < 0)) {
+			dropbear_exit("error changing user group");
+		}
+		if (setuid(ses.authstate.pw->pw_uid) < 0) {
+			dropbear_exit("error changing user");
+		}
+	} else {
+		/* ... but if the daemon is the same uid as the requested uid, we don't
+		 * need to */
+
+		/* XXX - there is a minor issue here, in that if there are multiple
+		 * usernames with the same uid, but differing groups, then the
+		 * differing groups won't be set (as with initgroups()). The solution
+		 * is for the sysadmin not to give out the UID twice */
+		if (getuid() != ses.authstate.pw->pw_uid) {
+			dropbear_exit("couldn't	change user as non-root");
+		}
+	}
+
+	/* an empty shell should be interpreted as "/bin/sh" */
+	if (ses.authstate.pw->pw_shell[0] == '\0') {
+		usershell = "/bin/sh";
+	} else {
+		usershell = ses.authstate.pw->pw_shell;
+	}
+
+	/* set env vars */
+	addnewvar("USER", ses.authstate.pw->pw_name);
+	addnewvar("LOGNAME", ses.authstate.pw->pw_name);
+	addnewvar("HOME", ses.authstate.pw->pw_dir);
+	addnewvar("SHELL", usershell);
+	if (chansess->term != NULL) {
+		addnewvar("TERM", chansess->term);
+	}
+
+	/* change directory */
+	if (chdir(ses.authstate.pw->pw_dir) < 0) {
+		dropbear_exit("error changing directory");
+	}
+
+#ifndef DISABLE_X11FWD
+	/* set up X11 forwarding if enabled */
+	x11setauth(chansess);
+#endif
+#ifndef DISABLE_AGENTFWD
+	/* set up agent env variable */
+	agentset(chansess);
+#endif
+
+	/* Re-enable SIGPIPE for the executed process */
+	if (signal(SIGPIPE, SIG_DFL) == SIG_ERR) {
+		dropbear_exit("signal() error");
+	}
+
+	baseshell = basename(usershell);
+
+	if (chansess->cmd != NULL) {
+		argv[0] = baseshell;
+	} else {
+		/* a login shell should be "-bash" for "/bin/bash" etc */
+		int len = strlen(baseshell) + 2; /* 2 for "-" */
+		argv[0] = (char*)m_malloc(len);
+		snprintf(argv[0], len, "-%s", baseshell);
+	}
+
+	if (chansess->cmd != NULL) {
+		argv[1] = "-c";
+		argv[2] = chansess->cmd;
+		argv[3] = NULL;
+	} else {
+		/* construct a shell of the form "-bash" etc */
+		argv[1] = NULL;
+	}
+
+	execv(usershell, argv);
+
+	/* only reached on error */
+	dropbear_exit("child failed");
+}
+
+const struct ChanType svrchansess = {
+	0, /* sepfds */
+	"session", /* name */
+	newchansess, /* inithandler */
+	sesscheckclose, /* checkclosehandler */
+	chansessionrequest, /* reqhandler */
+	closechansess, /* closehandler */
+};
+
+
+/* Set up the general chansession environment, in particular child-exit
+ * handling */
+void svr_chansessinitialise() {
+
+	struct sigaction sa_chld;
+
+	/* single child process intially */
+	svr_ses.childpids = (struct ChildPid*)m_malloc(sizeof(struct ChildPid));
+	svr_ses.childpids[0].pid = -1; /* unused */
+	svr_ses.childpids[0].chansess = NULL;
+	svr_ses.childpidsize = 1;
+	svr_ses.lastexit.exitpid = -1; /* Nothing has exited yet */
+	sa_chld.sa_handler = sesssigchild_handler;
+	sa_chld.sa_flags = SA_NOCLDSTOP;
+	if (sigaction(SIGCHLD, &sa_chld, NULL) < 0) {
+		dropbear_exit("signal() error");
+	}
+	
+}
+
+/* add a new environment variable, allocating space for the entry */
+void addnewvar(const char* param, const char* var) {
+
+	char* newvar = NULL;
+	int plen, vlen;
+
+	plen = strlen(param);
+	vlen = strlen(var);
+
+	newvar = m_malloc(plen + vlen + 2); /* 2 is for '=' and '\0' */
+	memcpy(newvar, param, plen);
+	newvar[plen] = '=';
+	memcpy(&newvar[plen+1], var, vlen);
+	newvar[plen+vlen+1] = '\0';
+	/* newvar is leaked here, but that's part of putenv()'s semantics */
+	if (putenv(newvar) < 0) {
+		dropbear_exit("environ error");
+	}
+}