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/* Simple login program for use with ttyd
Original login does not work well with ttyd
Build with:
cc -Wall slogin.c -o slogin -lpam -lpam_misc -lutil
Elmar Klausmeier, 24-Jul-2020
*/
#include <stdio.h>
#include <stdlib.h> // for setenv()
#include <security/pam_appl.h>
#include <security/pam_misc.h>
#include <sys/types.h>
#include <sys/time.h> // for gettimeofday()
#include <sys/wait.h> // for wait()
#include <pwd.h> // for getpwnam()
#include <grp.h> // for initgroups()
#include <errno.h>
#include <utmp.h> // for logwtmp() + login() + logout()
//#include <utmpx.h> // for struct utmpx, in Linux utmpx and utmp are the same
extern char **environ;
int main(int argc, char *argv[]) {
int rc, flag=1;
struct pam_conv conv = { misc_conv, NULL }; // Linux-PAM conversation function
pam_handle_t *pamh = NULL;
char *p, username[256], arg0[256], *termenv;
struct passwd *pwd;
struct utmp ut;
struct timeval tv;
pid_t pid = getpid(), child_pid;
while (flag) {
rc = pam_start("login",NULL,&conv,&pamh);
if (rc != PAM_SUCCESS) {
printf("%s: pam_start() returned %d = %s\n",
argv[0],rc,pam_strerror(pamh,rc));
pam_end(pamh,0);
return 1;
}
rc = pam_authenticate(pamh, 0);
if (rc != PAM_SUCCESS) {
pam_get_item(pamh, PAM_USER, (const void**)&p);
printf("%s: pam_authenticate() for |%s| returned %d = %s\n",
argv[0],p,rc,pam_strerror(pamh,rc));
// log in btmp, see log_btmp() in login.c
memset(&ut, 0, sizeof(ut));
strncpy(ut.ut_user,p ? p : "(unknown)",UT_NAMESIZE);
ut.ut_user[UT_NAMESIZE] = '\0';
strcpy(ut.ut_line,"Hiawatha-ttyd");
gettimeofday(&tv, NULL);
ut.ut_tv.tv_sec = tv.tv_sec;
ut.ut_tv.tv_usec = tv.tv_usec;
ut.ut_type = LOGIN_PROCESS;
ut.ut_pid = pid;
strcpy(ut.ut_host,"Hiawatha-localhost");
updwtmp("/var/log/btmp", &ut);
} else {
rc = pam_get_item(pamh, PAM_USER, (const void**)&p);
if (rc != PAM_SUCCESS) {
printf("%s: pam_get_item() returned %d = %s\n",
argv[0],rc,pam_strerror(pamh,rc));
pam_end(pamh,0);
return 2;
}
if (p[0] == '\0') return 3;
if (strlen(p) > 255) return 4;
strcpy(username,p);
flag = 0;
}
rc = pam_end(pamh, 0);
if (rc != PAM_SUCCESS) {
printf("%s: pam_end() returned %d = %s\n",
argv[0],rc,pam_strerror(pamh,rc));
return 3;
}
}
printf("username = |%s|\n",username);
if ((pwd = getpwnam(username)) == NULL) return 4;
printf("pw_uid = %d, pw_gid = %d, pw_shell = %s\n",
pwd->pw_uid, pwd->pw_gid, pwd->pw_shell);
//logwtmp("ttyd",username,"hiawatha");
memset(&ut, 0, sizeof(ut));
strncpy(ut.ut_user,username,UT_NAMESIZE);
ut.ut_user[UT_NAMESIZE] = '\0';
//strcpy(ut.ut_line,"Hiawatha-ttyd");
strcpy(ut.ut_line,ttyname(1)+5);
gettimeofday(&tv, NULL);
ut.ut_tv.tv_sec = tv.tv_sec;
ut.ut_tv.tv_usec = tv.tv_usec;
ut.ut_type = LOGIN_PROCESS;
ut.ut_pid = pid;
strcpy(ut.ut_host,"Hiawatha-localhost");
//updwtmp("/run/utmp", &ut);
//updwtmp("/var/log/wtmp", &ut);
login(&ut); // works well for root
printf("ut_user=|%s|, ut_line=|%s|, ut_pid=%d, ut_host=|%s|\n",
ut.ut_user, ut.ut_line, ut.ut_pid, ut.ut_host);
if ((child_pid = fork()) < 0) {
printf("%s: cannot fork, %s\n", argv[0],strerror(errno));
return 4;
} else if (child_pid > 0) { // parent
close(0);
close(1);
close(2);
// wait as long as any child is there
while (wait(NULL) == -1 && errno == EINTR)
;
logout(ut.ut_line);
return 0;
}
// Child
setsid(); // start new session
/* Copied from login.c
* For root we don't call initgroups, instead we call setgroups with
* group 0. This avoids the need to step through the whole group file,
* which can cause problems if NIS, NIS+, LDAP or something similar
* is used and the machine has network problems.
*/
rc = pwd->pw_uid ? initgroups(username, pwd->pw_gid) : setgroups(0, NULL);
if (rc) {
printf("%s: initgroups() returned %d, %s\n",
argv[0], rc, strerror(errno));
return 8;
}
termenv = getenv("TERM");
environ = calloc(1,sizeof(char*));
setenv("HOME",pwd->pw_dir,1);
setenv("USER",pwd->pw_name,1);
setenv("SHELL",pwd->pw_shell,1);
setenv("TERM",termenv ? termenv : "dumb",1);
// First change group, then uid because non-root cannot set group
if ((rc = setgid(pwd->pw_gid)) != 0) {
printf("%s: setgid() returned %d, %s\n",
argv[0], rc, strerror(errno));
return 9;
}
if ((rc = setuid(pwd->pw_uid)) != 0) {
printf("%s: setuid() returned %d, %s\n",
argv[0], rc, strerror(errno));
return 10;
}
if ((rc = chdir(pwd->pw_dir)) != 0) {
printf("%s: chdir(\"%s\") returned %d, %s\n",
argv[0], pwd->pw_dir, rc, strerror(errno));
return 11;
}
if (strchr(pwd->pw_shell, ' ')) {
printf("%s: pw_shell=|%s| contains space\n", argv[0], pwd->pw_shell);
//return 12;
}
arg0[0] = '-';
strncpy(arg0+1,(p = strrchr(pwd->pw_shell,'/')) ? p+1 : pwd->pw_shell,254);
arg0[255] = '\0';
execl(pwd->pw_shell,arg0,NULL);
return 0; // never reached after execl()
}
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