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|
/*
* 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 void get_termmodes(struct ChanSess *chansess);
/* required to clear environment */
extern char** environ;
static int sesscheckclose(struct Channel *channel) {
struct ChanSess *chansess = (struct ChanSess*)channel->typedata;
return chansess->exit.exitpid != -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) {
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';
if (putenv(newvar) < 0) {
dropbear_exit("environ error");
}
}
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