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shellinabox/shellinabox/launcher.c
zodiac 48a3768baa Found a work-around for gcc warning about type-punning. 
git-svn-id: https://shellinabox.googlecode.com/svn/trunk@29 0da03de8-d603-11dd-86c2-0f8696b7b6f9
2009-01-05 20:42:07 +00:00

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// launcher.c -- Launch services from a privileged process
// Copyright (C) 2008-2009 Markus Gutschke <markus@shellinabox.com>
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License version 2 as
// published by the Free Software Foundation.
//
// 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.,
// 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
//
// In addition to these license terms, the author grants the following
// additional rights:
//
// If you modify this program, or any covered work, by linking or
// combining it with the OpenSSL project's OpenSSL library (or a
// modified version of that library), containing parts covered by the
// terms of the OpenSSL or SSLeay licenses, the author
// grants you additional permission to convey the resulting work.
// Corresponding Source for a non-source form of such a combination
// shall include the source code for the parts of OpenSSL used as well
// as that of the covered work.
//
// You may at your option choose to remove this additional permission from
// the work, or from any part of it.
//
// It is possible to build this program in a way that it loads OpenSSL
// libraries at run-time. If doing so, the following notices are required
// by the OpenSSL and SSLeay licenses:
//
// This product includes software developed by the OpenSSL Project
// for use in the OpenSSL Toolkit. (http://www.openssl.org/)
//
// This product includes cryptographic software written by Eric Young
// (eay@cryptsoft.com)
//
//
// The most up-to-date version of this program is always available from
// http://shellinabox.com
#define _GNU_SOURCE
#include <dirent.h>
#include <dlfcn.h>
#include <fcntl.h>
#include <grp.h>
#include <pwd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/utsname.h>
#include <termios.h>
#include <unistd.h>
#include <utmpx.h>
#if defined(HAVE_SECURITY_PAM_APPL_H) && defined(HAVE_SECURITY_PAM_MISC_H)
#include <security/pam_appl.h>
#include <security/pam_misc.h>
#else
struct pam_message;
struct pam_response;
struct pam_conv;
typedef struct pam_handle pam_handle_t;
#endif
#if defined(HAVE_PTHREAD_H)
#include <pthread.h>
extern int pthread_once(pthread_once_t *, void (*)(void))__attribute__((weak));
#endif
#include "shellinabox/launcher.h"
#include "shellinabox/privileges.h"
#include "shellinabox/service.h"
#include "libhttp/hashmap.h"
#include "logging/logging.h"
// If PAM support is available, take advantage of it. Otherwise, silently fall
// back on legacy operations for session management.
static int (*x_pam_acct_mgmt)(pam_handle_t *, int);
static int (*x_pam_authenticate)(pam_handle_t *, int);
static int (*x_pam_close_session)(pam_handle_t *, int);
static int (*x_pam_end)(pam_handle_t *, int);
static int (*x_pam_get_item)(const pam_handle_t *, int, const void **);
static int (*x_pam_open_session)(pam_handle_t *, int);
static int (*x_pam_set_item)(pam_handle_t *, int, const void *);
static int (*x_pam_start)(const char *, const char *, const struct pam_conv *,
pam_handle_t **);
static int (*x_misc_conv)(int, const struct pam_message **,
struct pam_response **, void *);
// Older versions of glibc might not support fdopendir(). That's OK, we can
// work around the lack of it, at a small performance loss.
extern DIR *fdopendir(int) __attribute__((weak));
static int launcher = -1;
static uid_t restricted;
static void *loadSymbol(const char *lib, const char *fn) {
void *dl = RTLD_DEFAULT;
void *rc = dlsym(dl, fn);
if (!rc) {
dl = dlopen(lib, RTLD_LAZY|RTLD_GLOBAL|RTLD_NOLOAD);
if (dl == NULL) {
dl = dlopen(lib, RTLD_LAZY|RTLD_GLOBAL);
}
if (dl != NULL) {
rc = dlsym(dl, fn);
}
}
return rc;
}
static void loadPAM(void) {
check(!x_pam_start);
check(!x_misc_conv);
struct {
union {
void *avoid_gcc_warning_about_type_punning;
void **var;
};
const char *lib;
const char *fn;
} symbols[] = {
{ { &x_pam_acct_mgmt }, "libpam.so", "pam_acct_mgmt" },
{ { &x_pam_authenticate }, "libpam.so", "pam_authenticate" },
{ { &x_pam_close_session }, "libpam.so", "pam_close_session" },
{ { &x_pam_end }, "libpam.so", "pam_end" },
{ { &x_pam_get_item }, "libpam.so", "pam_get_item" },
{ { &x_pam_open_session }, "libpam.so", "pam_open_session" },
{ { &x_pam_set_item }, "libpam.so", "pam_set_item" },
{ { &x_pam_start }, "libpam.so", "pam_start" },
{ { &x_misc_conv }, "libpam_misc.so", "misc_conv" }
};
for (int i = 0; i < sizeof(symbols)/sizeof(symbols[0]); i++) {
if (!(*symbols[i].var = loadSymbol(symbols[i].lib, symbols[i].fn))) {
debug("Failed to load PAM support. Could not find \"%s\"",
symbols[i].fn);
for (int j = 0; j < sizeof(symbols)/sizeof(symbols[0]); j++) {
*symbols[j].var = NULL;
}
break;
}
}
debug("Loaded PAM suppport");
}
int supportsPAM(void) {
#if defined(HAVE_SECURITY_PAM_APPL_H) && defined(HAVE_SECURITY_PAM_MISC_H)
// We want to call loadPAM() exactly once. For single-threaded applications,
// this is straight-forward. For threaded applications, we need to call
// pthread_once(), instead. We perform run-time checks for whether we are
// single- or multi-threaded, so that the same code can be used.
#if defined(HAVE_PTHREAD_H)
if (!!&pthread_once) {
static pthread_once_t once = PTHREAD_ONCE_INIT;
pthread_once(&once, loadPAM);
} else
#endif
{
static int initialized;
if (!initialized) {
initialized = 1;
loadPAM();
}
}
return x_misc_conv && x_pam_start;
#else
return 0;
#endif
}
int launchChild(int service, struct Session *session) {
if (launcher < 0) {
errno = EINVAL;
return -1;
}
struct LaunchRequest request = {
.service = service,
.width = session->width,
.height = session->height };
strncat(request.peerName, httpGetPeerName(session->http),
sizeof(request.peerName));
if (NOINTR(write(launcher, &request, sizeof(request))) != sizeof(request)) {
return -1;
}
pid_t pid;
char cmsg_buf[CMSG_SPACE(sizeof(int))];
struct iovec iov = { 0 };
struct msghdr msg = { 0 };
iov.iov_base = &pid;
iov.iov_len = sizeof(pid);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
msg.msg_control = &cmsg_buf;
msg.msg_controllen = sizeof(cmsg_buf);
int bytes = NOINTR(recvmsg(launcher, &msg, 0));
if (bytes < 0) {
return -1;
}
check(bytes == sizeof(pid));
struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
check(cmsg);
check(cmsg->cmsg_level == SOL_SOCKET);
check(cmsg->cmsg_type == SCM_RIGHTS);
session->pty = *(int *)CMSG_DATA(cmsg);
return pid;
}
struct Utmp {
const char pid[32];
int pty;
int useLogin;
struct utmpx utmpx;
};
static HashMap *childProcesses;
void initUtmp(struct Utmp *utmp, int useLogin, const char *ptyPath,
const char *peerName) {
memset(utmp, 0, sizeof(struct Utmp));
utmp->pty = -1;
utmp->useLogin = useLogin;
utmp->utmpx.ut_type = useLogin ? LOGIN_PROCESS : USER_PROCESS;
dcheck(!strncmp(ptyPath, "/dev/pts", 8));
strncat(&utmp->utmpx.ut_line[0], ptyPath + 5, sizeof(utmp->utmpx.ut_line));
strncat(&utmp->utmpx.ut_id[0], ptyPath + 8, sizeof(utmp->utmpx.ut_id));
strncat(&utmp->utmpx.ut_user[0], "SHELLINABOX", sizeof(utmp->utmpx.ut_user));
strncat(&utmp->utmpx.ut_host[0], peerName, sizeof(utmp->utmpx.ut_host));
struct timeval tv;
check(!gettimeofday(&tv, NULL));
utmp->utmpx.ut_tv.tv_sec = tv.tv_sec;
utmp->utmpx.ut_tv.tv_usec = tv.tv_usec;
}
struct Utmp *newUtmp(int useLogin, const char *ptyPath,
const char *peerName) {
struct Utmp *utmp;
check(utmp = malloc(sizeof(struct Utmp)));
initUtmp(utmp, useLogin, ptyPath, peerName);
return utmp;
}
void destroyUtmp(struct Utmp *utmp) {
if (utmp) {
if (utmp->pty >= 0) {
utmp->utmpx.ut_type = DEAD_PROCESS;
memset(&utmp->utmpx.ut_user, 0, sizeof(utmp->utmpx.ut_user));
memset(&utmp->utmpx.ut_host, 0, sizeof(utmp->utmpx.ut_host));
struct timeval tv;
check(!gettimeofday(&tv, NULL));
utmp->utmpx.ut_tv.tv_sec = tv.tv_sec;
utmp->utmpx.ut_tv.tv_usec = tv.tv_usec;
// Temporarily regain privileges to update the utmp database
uid_t r_uid, e_uid, s_uid;
uid_t r_gid, e_gid, s_gid;
check(!getresuid(&r_uid, &e_uid, &s_uid));
check(!getresgid(&r_gid, &e_gid, &s_gid));
setresuid(0, 0, 0);
setresgid(0, 0, 0);
setutxent();
pututxline(&utmp->utmpx);
endutxent();
if (!utmp->useLogin) {
updwtmpx("/var/log/wtmp", &utmp->utmpx);
}
// Switch back to the lower privileges
check(!setresgid(r_gid, e_gid, s_gid));
check(!setresuid(r_uid, e_uid, s_uid));
NOINTR(close(utmp->pty));
}
}
}
void deleteUtmp(struct Utmp *utmp) {
destroyUtmp(utmp);
free(utmp);
}
static void destroyUtmpHashEntry(void *arg, char *key, char *value) {
deleteUtmp((struct Utmp *)value);
}
void closeAllFds(int *exceptFds, int num) {
// Close all file handles. If possible, scan through "/proc/self/fd" as
// that is faster than calling close() on all possible file handles.
int nullFd = open("/dev/null", O_RDWR);
int dirFd = !&fdopendir ? -1 : open("/proc/self/fd", O_RDONLY);
if (dirFd < 0) {
for (int i = sysconf(_SC_OPEN_MAX); --i > 0; ) {
if (i != nullFd) {
for (int j = 0; j < num; j++) {
if (i == exceptFds[j]) {
goto no_close_1;
}
}
// Closing handles 0..2 is never a good idea. Instead, redirect them
// to /dev/null
if (i <= 2) {
NOINTR(dup2(nullFd, i));
} else {
NOINTR(close(i));
}
}
no_close_1:;
}
} else {
DIR *dir;
check(dir = fdopendir(dirFd));
struct dirent de, *res;
while (!readdir_r(dir, &de, &res) && res) {
if (res->d_name[0] < '0')
continue;
int fd = atoi(res->d_name);
if (fd != nullFd && fd != dirFd) {
for (int j = 0; j < num; j++) {
if (fd == exceptFds[j]) {
goto no_close_2;
}
}
// Closing handles 0..2 is never a good idea. Instead, redirect them
// to /dev/null
if (fd <= 2) {
NOINTR(dup2(nullFd, fd));
} else {
NOINTR(close(fd));
}
}
no_close_2:;
}
check(!closedir(dir));
}
if (nullFd > 2) {
check(!close(nullFd));
}
}
static int forkPty(int *pty, int useLogin, struct Utmp **utmp,
const char *peerName) {
int slave;
char ptyPath[PATH_MAX];
if ((*pty = getpt()) < 0 ||
grantpt(*pty) < 0 ||
unlockpt(*pty) < 0 ||
ptsname_r(*pty, ptyPath, sizeof(ptyPath)) < 0 ||
(slave = NOINTR(open(ptyPath, O_RDWR|O_NOCTTY))) < 0) {
if (*pty >= 0) {
NOINTR(close(*pty));
}
*pty = -1;
*utmp = NULL;
return -1;
}
// Fill in utmp entry
*utmp = newUtmp(useLogin, ptyPath, peerName);
// Now, fork off the child process
pid_t pid;
if ((pid = fork()) < 0) {
NOINTR(close(slave));
NOINTR(close(*pty));
*pty = -1;
deleteUtmp(*utmp);
*utmp = NULL;
return -1;
} else if (pid == 0) {
pid = getpid();
snprintf((char *)&(*utmp)->pid[0], sizeof((*utmp)->pid), "%d", pid);
(*utmp)->utmpx.ut_pid = pid;
(*utmp)->pty = slave;
closeAllFds((int []){ slave }, 1);
// Become the session/process-group leader
setsid();
setpgid(0, 0);
// Redirect standard I/O to the pty
dup2(slave, 0);
dup2(slave, 1);
dup2(slave, 2);
if (slave > 2) {
NOINTR(close(slave));
}
*pty = 0;
// Force the pty to be our control terminal
NOINTR(close(NOINTR(open(ptyPath, O_RDWR))));
return 0;
} else {
snprintf((char *)&(*utmp)->pid[0], sizeof((*utmp)->pid), "%d", pid);
(*utmp)->utmpx.ut_pid = pid;
(*utmp)->pty = *pty;
fcntl(*pty, F_SETFL, O_NONBLOCK|O_RDWR);
NOINTR(close(slave));
return pid;
}
}
static const struct passwd *getPWEnt(uid_t uid) {
struct passwd pwbuf, *pw;
char *buf;
int len = sysconf(_SC_GETPW_R_SIZE_MAX);
check(len > 0);
check(buf = malloc(len));
check(!getpwuid_r(uid, &pwbuf, buf, len, &pw) && pw);
struct passwd *passwd;
check(passwd = malloc(sizeof(struct passwd) +
strlen(pw->pw_name) +
strlen(pw->pw_passwd) +
strlen(pw->pw_gecos) +
strlen(pw->pw_dir) +
strlen(pw->pw_shell) + 5));
passwd->pw_uid = pw->pw_uid;
passwd->pw_gid = pw->pw_gid;
strcpy(passwd->pw_shell = strrchr(
strcpy(passwd->pw_dir = strrchr(
strcpy(passwd->pw_gecos = strrchr(
strcpy(passwd->pw_passwd = strrchr(
strcpy(passwd->pw_name = (char *)(passwd + 1),
pw->pw_name), '\000') + 1,
pw->pw_passwd), '\000') + 1,
pw->pw_gecos), '\000') + 1,
pw->pw_dir), '\000') + 1,
pw->pw_shell);
free(buf);
return passwd;
}
static void sigAlrmHandler(int sig, siginfo_t *info, void *unused) {
puts("\nLogin timed out after 60 seconds.");
_exit(1);
}
static pam_handle_t *internalLogin(struct Service *service, struct Utmp *utmp,
char ***environment) {
// Time out after 60 seconds
struct sigaction sa;
memset(&sa, 0, sizeof(sa));
sa.sa_flags = SA_SIGINFO;
sa.sa_sigaction = sigAlrmHandler;
check(!sigaction(SIGALRM, &sa, NULL));
alarm(60);
// Use PAM to negotiate user authentication and authorization
const struct passwd *pw;
pam_handle_t *pam = NULL;
struct pam_conv conv = { .conv = x_misc_conv };
if (service->authUser) {
check(supportsPAM());
check(x_pam_start("shellinabox", NULL, &conv, &pam) == PAM_SUCCESS);
// Change the prompt to include the host name
struct utsname uts;
check(!uname(&uts));
const char *origPrompt;
check(x_pam_get_item(pam, PAM_USER_PROMPT, (void *)&origPrompt) ==
PAM_SUCCESS);
char *prompt;
check(prompt = stringPrintf(NULL, "%s %s", uts.nodename,
origPrompt ? origPrompt : "login: "));
check(x_pam_set_item(pam, PAM_USER_PROMPT, prompt) == PAM_SUCCESS);
// Up to three attempts to enter the user id and password
for (int i = 0;;) {
check(x_pam_set_item(pam, PAM_USER, NULL) == PAM_SUCCESS);
int rc;
if ((rc = x_pam_authenticate(pam, PAM_SILENT)) ==
PAM_SUCCESS &&
(geteuid() ||
(rc = x_pam_acct_mgmt(pam, PAM_SILENT)) ==
PAM_SUCCESS)) {
break;
}
if (++i == 3) {
// Quit if login failed.
puts("\nMaximum number of tries exceeded (3)");
x_pam_end(pam, rc);
_exit(1);
} else {
puts("\nLogin incorrect");
}
}
check(x_pam_set_item(pam, PAM_USER_PROMPT, "login: ") == PAM_SUCCESS);
free(prompt);
// Retrieve user id, and group id.
const char *name;
check(x_pam_get_item(pam, PAM_USER, (void *)&name) == PAM_SUCCESS);
pw = getPWEnt(getUserId(name));
check(service->uid < 0);
check(service->gid < 0);
check(!service->user);
check(!service->group);
service->uid = pw->pw_uid;
service->gid = pw->pw_gid;
check(service->user = strdup(pw->pw_name));
service->group = getGroupName(pw->pw_gid);
} else {
check(service->uid >= 0);
check(service->gid >= 0);
check(service->user);
check(service->group);
if (supportsPAM()) {
check(x_pam_start("shellinabox", service->user, &conv, &pam) ==
PAM_SUCCESS);
int rc;
// PAM account management requires root access. Just skip it, if we
// are running with lower privileges.
if (geteuid() &&
(rc = x_pam_acct_mgmt(pam, PAM_SILENT)) !=
PAM_SUCCESS) {
x_pam_end(pam, rc);
_exit(1);
}
}
pw = getPWEnt(service->uid);
}
if (restricted &&
(service->uid != restricted || service->gid != pw->pw_gid)) {
puts("\nAccess denied!");
x_pam_end(pam, PAM_SUCCESS);
_exit(1);
}
if (pam) {
check(x_pam_set_item(pam, PAM_TTY, (const void **)utmp->utmpx.ut_line) ==
PAM_SUCCESS);
}
// Retrieve supplementary group ids.
int ngroups = 0;
getgrouplist(service->user, pw->pw_gid, NULL, &ngroups);
check(ngroups >= 0);
if (ngroups > 0) {
// Set supplementary group ids
gid_t *groups;
check(groups = malloc((ngroups + 1) * sizeof(gid_t)));
groups[ngroups] = service->gid;
check(getgrouplist(service->user, pw->pw_gid, groups, &ngroups) ==
ngroups);
// Make sure that any group that was requested on the command line is
// included, if it is not one of the normal groups for this user.
for (int i = 0; ; i++) {
if (i == ngroups) {
ngroups++;
break;
} else if (groups[i] == service->gid) {
break;
}
}
setgroups(ngroups, groups);
free(groups);
}
// Add standard environment variables
int numEnvVars = 0;
for (char **e = *environment; *e; numEnvVars++, e++) {
}
check(*environment = realloc(*environment,
(numEnvVars + 6)*sizeof(char *)));
(*environment)[numEnvVars++] = stringPrintf(NULL, "HOME=%s", pw->pw_dir);
(*environment)[numEnvVars++] = stringPrintf(NULL, "SHELL=%s", pw->pw_shell);
check(
(*environment)[numEnvVars++] = strdup(
"PATH=/usr/local/bin:/usr/bin:/bin:/usr/games"));
(*environment)[numEnvVars++] = stringPrintf(NULL, "LOGNAME=%s",
service->user);
(*environment)[numEnvVars++] = stringPrintf(NULL, "USER=%s", service->user);
(*environment)[numEnvVars++] = NULL;
free((void *)pw);
// Update utmp/wtmp entries
memset(&utmp->utmpx.ut_user, 0, sizeof(utmp->utmpx.ut_user));
strncat(&utmp->utmpx.ut_user[0], service->user, sizeof(utmp->utmpx.ut_user));
setutxent();
pututxline(&utmp->utmpx);
endutxent();
updwtmpx("/var/log/wtmp", &utmp->utmpx);
alarm(0);
return pam;
}
static void destroyVariableHashEntry(void *arg, char *key, char *value) {
free(key);
free(value);
}
static void execService(int width, int height, struct Service *service,
const char *peerName, char **environment) {
// Create a hash table with all the variables that we can expand. This
// includes all environment variables being passed to the child.
HashMap *vars;
check(vars = newHashMap(destroyVariableHashEntry, NULL));
for (char **e = environment; *e; e++) {
char *ptr = strchr(*e, '=');
char *key, *value;
if (!ptr) {
check(key = strdup(*e));
check(value = strdup(""));
} else {
check(key = malloc(ptr - *e + 1));
memcpy(key, *e, ptr - *e);
key[ptr - *e] = '\000';
check(value = strdup(ptr + 1));
}
// All of our variables are lower-case
for (ptr = key; *ptr; ptr++) {
if (*ptr >= 'A' && *ptr <= 'Z') {
*ptr += 'a' - 'A';
}
}
addToHashMap(vars, key, value);
}
char *key, *value;
check(key = strdup("gid"));
addToHashMap(vars, key, stringPrintf(NULL, "%d", service->gid));
check(key = strdup("group"));
check(value = strdup(service->group));
addToHashMap(vars, key, value);
check(key = strdup("peer"));
check(value = strdup(peerName));
addToHashMap(vars, key, value);
check(key = strdup("uid"));
addToHashMap(vars, key, stringPrintf(NULL, "%d", service->uid));
enum { ENV, ARGS } state = ENV;
enum { NONE, SINGLE, DOUBLE
} quote = NONE;
char *cmdline;
check(cmdline = strdup(service->cmdline));
int argc = 0;
char **argv;
check(argv = malloc(sizeof(char *)));
key = NULL;
value = NULL;
for (char *ptr = cmdline; ; ptr++) {
if (!key && *ptr && *ptr != ' ') {
key = ptr;
}
switch (*ptr) {
case '\'':
if (quote == SINGLE || quote == NONE) {
memmove(ptr, ptr + 1, strlen(ptr));
ptr--;
quote = quote == SINGLE ? NONE : SINGLE;
} else {
dcheck(quote == DOUBLE);
}
break;
case '\"':
if (quote == DOUBLE || quote == NONE) {
memmove(ptr, ptr + 1, strlen(ptr));
ptr--;
quote = quote == DOUBLE ? NONE : DOUBLE;
} else {
dcheck(quote == SINGLE);
}
break;
case '$':
if ((quote == NONE || quote == DOUBLE) && ptr[1] == '{') {
// Always treat environment variables as if they were quoted. There
// is not good reason for us to try to look for spaces within
// expanded environment variables. This just leads to subtle bugs.
char *end = ptr + 2;
while (*end && *end != '}') {
end++;
}
char ch = *end;
*end = '\000';
const char *repl = getFromHashMap(vars, ptr);
int replLen = repl ? strlen(repl) : 0;
*end = ch;
if (ch) {
end++;
}
memmove(ptr + replLen, end, strlen(end) + 1);
if (repl) {
memcpy(ptr, repl, replLen);
}
ptr += replLen;
}
break;
case '\\':
if (!ptr[1]) {
*ptr-- = '\000';
} else {
memmove(ptr, ptr + 1, strlen(ptr));
}
break;
case '=':
// This is the seperator between keys and values of any environment
// variable that we are asked to set.
if (state == ENV && quote == NONE && !value) {
*ptr = '\000';
value = ptr + 1;
}
break;
case ' ':
// If this space character is not quoted, this is the start of a new
// command line argument.
if (quote != NONE) {
break;
}
// Fall thru
case '\000':;
char ch = *ptr;
if (key) {
*ptr = '\000';
if (state == ENV && value) {
// Override an existing environment variable.
int numEnvVars = 0;
int len = strlen(key);
for (char **e = environment; *e; e++, numEnvVars++) {
if (!strncmp(*e, key, len) && (*e)[len] == '=') {
check(*e = realloc(*e, len + strlen(value) + 2));
strcpy((*e) + len + 1, value);
numEnvVars = -1;
break;
}
}
// Add a new environment variable
if (numEnvVars >= 0) {
check(environment = realloc(environment,
(numEnvVars + 2)*sizeof(char *)));
value[-1] = '=';
environment[numEnvVars++] = strdup(key);
environment[numEnvVars] = NULL;
}
} else {
// Add entry to argv.
state = ARGS;
argv[argc++] = key;
check(argv = realloc(argv, (argc + 1)*sizeof(char *)));
}
}
key = NULL;
value = NULL;
if (!ch) {
goto done;
}
break;
default:
break;
}
}
done:
argv[argc] = NULL;
deleteHashMap(vars);
check(argc);
extern char **environ;
environ = environment;
char *cmd = strrchr(argv[0], '/');
execvp(cmd ? cmd + 1: argv[0], argv);
}
void setWindowSize(int pty, int width, int height) {
if (width > 0 && height > 0) {
struct winsize win;
win.ws_row = height;
win.ws_col = width;
win.ws_xpixel = 0;
win.ws_ypixel = 0;
ioctl(pty, TIOCSWINSZ, &win);
}
}
static void childProcess(struct Service *service, int width, int height,
struct Utmp *utmp, const char *peerName) {
// Set initial window size
setWindowSize(0, width, height);
// Set up environment variables
static const char *legalEnv[] = { "TZ", "HZ", NULL };
char **environment;
check(environment = malloc(2*sizeof(char *)));
int numEnvVars = 1;
environment[0] = "TERM=xterm";
if (width > 0 && height > 0) {
numEnvVars += 2;
check(environment = realloc(environment,
(numEnvVars + 1)*sizeof(char *)));
environment[numEnvVars-2] = stringPrintf(NULL, "COLUMNS=%d", width);
environment[numEnvVars-1] = stringPrintf(NULL, "LINES=%d", height);
}
for (int i = 0; legalEnv[i]; i++) {
char *value = getenv(legalEnv[i]);
if (value) {
numEnvVars++;
check(environment = realloc(environment,
(numEnvVars + 1)*sizeof(char *)));
environment[numEnvVars-1] = stringPrintf(NULL, "%s=%s",
legalEnv[i], value);
}
}
environment[numEnvVars] = NULL;
// Set initial terminal settings
struct termios tt;
tcgetattr(0, &tt);
cfsetispeed(&tt, 38400);
cfsetospeed(&tt, 38400);
tt.c_iflag = TTYDEF_IFLAG & ~ISTRIP;
tt.c_oflag = TTYDEF_OFLAG;
tt.c_lflag = TTYDEF_LFLAG;
tt.c_cflag = (TTYDEF_CFLAG & ~(CS7|PARENB|HUPCL)) | CS8;
tt.c_cc[VERASE] = '\x7F';
tcsetattr(0, TCSAFLUSH, &tt);
// Assert root privileges in order to update utmp entry.
setresuid(0, 0, 0);
setresgid(0, 0, 0);
setutxent();
struct utmpx utmpx = utmp->utmpx;
if (service->useLogin || service->authUser) {
utmpx.ut_type = LOGIN_PROCESS;
memset(utmpx.ut_host, 0, sizeof(utmpx.ut_host));
}
pututxline(&utmpx);
endutxent();
if (!utmp->useLogin) {
memset(&utmpx.ut_user, 0, sizeof(utmpx.ut_user));
strncat(&utmpx.ut_user[0], "LOGIN", sizeof(utmpx.ut_user));
updwtmpx("/var/log/wtmp", &utmpx);
}
// Create session. We might have to fork another process as PAM wants us
// to close the session when the child terminates. And we must retain
// permissions, as session closure could require root permissions.
// None of this really applies if we are running as an unprivileged user.
// In that case, we do not bother about session management.
if (!service->useLogin) {
pam_handle_t *pam = internalLogin(service, utmp, &environment);
if (pam && !geteuid()) {
check(x_pam_open_session(pam, PAM_SILENT) == PAM_SUCCESS);
pid_t pid = fork();
switch (pid) {
case -1:
_exit(1);
case 0:
break;
default:;
// Finish all pending PAM operations.
int status, rc;
check(waitpid(pid, &status, 0) == pid);
check((rc = x_pam_close_session(pam, PAM_SILENT)) ==
PAM_SUCCESS);
check(x_pam_end(pam, rc) == PAM_SUCCESS);
_exit(WIFEXITED(status) ? WEXITSTATUS(status) : -WTERMSIG(status));
}
}
}
// Change user and group ids
check(!setresgid(service->gid, service->gid, service->gid));
check(!setresuid(service->uid, service->uid, service->uid));
// Change working directory
if (service->useHomeDir) {
check(!service->useLogin);
const struct passwd *pw = getPWEnt(getuid());
check(!service->cwd);
check(service->cwd = strdup(pw->pw_dir));
free((void *)pw);
}
check(service->cwd);
if (!*service->cwd || *service->cwd != '/' || chdir(service->cwd)) {
check(service->cwd = realloc((char *)service->cwd, 2));
strcpy((char *)service->cwd, "/");
puts("No directory, logging in with HOME=/");
check(!chdir("/"));
for (int i = 0; environment[i]; i++) {
if (!strncmp(environment[i], "HOME=", 5)) {
free(environment[i]);
check(environment[i] = strdup("HOME=/"));
break;
}
}
}
// Finally, launch the child process.
if (service->useLogin) {
execle("/bin/login", "login", "-p", "-h", peerName, NULL, environment);
} else {
execService(width, height, service, peerName, environment);
}
_exit(1);
}
static void sigChildHandler(int sig, siginfo_t *info, void *unused) {
}
static void launcherDaemon(int fd) {
struct sigaction sa;
memset(&sa, 0, sizeof(sa));
sa.sa_flags = SA_NOCLDSTOP | SA_SIGINFO;
sa.sa_sigaction = sigChildHandler;
check(!sigaction(SIGCHLD, &sa, NULL));
struct LaunchRequest request;
for (;;) {
errno = 0;
int len = read(fd, &request, sizeof(request));
if (len != sizeof(request) && errno != EINTR) {
break;
}
// Check whether our read operation got interrupted, because a child
// has died.
int status;
pid_t pid;
while (NOINTR(pid = waitpid(-1, &status, WNOHANG)) > 0) {
if (WIFEXITED(pid) || WIFSIGNALED(pid)) {
char key[32];
snprintf(&key[0], sizeof(key), "%d", pid);
deleteFromHashMap(childProcesses, key);
}
}
if (len != sizeof(request)) {
continue;
}
check(request.service >= 0);
check(request.service < numServices);
// Sanitize the host name, so that we do not pass any unexpected characters
// to our child process.
request.peerName[sizeof(request.peerName)-1] = '\000';
for (char *s = request.peerName; *s; s++) {
if (!((*s >= '0' && *s <= '9') ||
(*s >= 'A' && *s <= 'Z') ||
(*s >= 'a' && *s <= 'z') ||
*s == '.' || *s == '-')) {
*s = '-';
}
}
// Fork and exec the child process.
int pty;
struct Utmp *utmp;
if ((pid = forkPty(&pty,
services[request.service]->useLogin,
&utmp, request.peerName)) < 0) {
} else if (pid == 0) {
childProcess(services[request.service], request.width, request.height,
utmp, request.peerName);
_exit(1);
} else {
// Remember the utmp entry so that we can clean up when the child
// terminates.
if (!childProcesses) {
childProcesses = newHashMap(destroyUtmpHashEntry, NULL);
}
addToHashMap(childProcesses, utmp->pid, (char *)utmp);
// Send file handle and process id back to parent
char cmsg_buf[CMSG_SPACE(sizeof(int))];
struct iovec iov = { 0 };
struct msghdr msg = { 0 };
iov.iov_base = &pid;
iov.iov_len = sizeof(pid);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
msg.msg_control = &cmsg_buf;
msg.msg_controllen = sizeof(cmsg_buf);
struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
check(cmsg);
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_RIGHTS;
cmsg->cmsg_len = CMSG_LEN(sizeof(int));
*(int *)CMSG_DATA(cmsg) = pty;
if (NOINTR(sendmsg(fd, &msg, 0)) != sizeof(pid)) {
break;
}
NOINTR(close(pty));
}
}
deleteHashMap(childProcesses);
_exit(0);
}
int forkLauncher(void) {
int pair[2];
check(!socketpair(AF_UNIX, SOCK_STREAM, 0, pair));
switch (fork()) {
case 0:;
// If our real-uid is not "root", then we should not allow anybody to
// login unauthenticated users as anyone other than their own.
uid_t tmp;
check(!getresuid(&restricted, &tmp, &tmp));
// Temporarily drop most permissions. We still retain the ability to
// switch back to root, which is necessary for launching "login".
lowerPrivileges();
NOINTR(close(pair[0]));
closeAllFds((int []){ pair[1] }, 1);
launcherDaemon(pair[1]);
fatal("exit() failed!");
case -1:
fatal("fork() failed!");
default:
NOINTR(close(pair[1]));
launcher = pair[0];
return launcher;
}
}
void terminateLauncher(void) {
if (launcher >= 0) {
NOINTR(close(launcher));
launcher = -1;
}
}
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