/* mlogin: minimalistic login */
/* Copyright (c) 2019 Ørjan Malde */
/* Released under LGPL, see COPYRIGHT.MLOGIN */
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <grp.h>
#include <pwd.h>
#include <errno.h>
#include <signal.h>
#ifdef __midipix__
#define IFLAG 1
#else
#define IFLAG 0
#endif
#include "login.h"
#include "motd.h"
#include "os/os.h"
static int do_login(struct passwd *pwd, int pflag)
{
char * comspec;
size_t envlen;
char ** envp;
char * envstrs;
char * envptrs[8];
char envbuff[3072];
if(*pwd->pw_shell == '\0')
pwd->pw_shell = "/bin/sh";
if(chdir(pwd->pw_dir) < 0) {
printf("no home directory %s!\n", pwd->pw_dir); /* handle -EPERM, -ENOMEM, -ESYMLNK */
if(chdir("/") == -1) {
printf("chdir failed with %s", strerror(errno));
return 0;
} else {
pwd->pw_dir = "/";
}
}
if(pflag) {
envp = environ;
(void)setenv("HOME", pwd->pw_dir, 1);
(void)setenv("SHELL", pwd->pw_shell, 1);
(void)setenv("TERM", "xterm", 0); /* TODO: this is 500% incorrect */
(void)setenv("LOGNAME", pwd->pw_name, 1);
(void)setenv("USER", pwd->pw_name, 1);
(void)setenv("PATH", "/local/sbin:/local/bin:/sbin:/bin", 0);
} else {
envlen = snprintf(envbuff,0,"HOME=%s",pwd->pw_dir) + 1;
envlen += snprintf(envbuff,0,"SHELL=%s",pwd->pw_shell) + 1;
envlen += snprintf(envbuff,0,"TERM=%s","xterm") + 1;
envlen += snprintf(envbuff,0,"LOGNAME=%s",pwd->pw_name) + 1;
envlen += snprintf(envbuff,0,"USER=%s",pwd->pw_name) + 1;
envlen += snprintf(envbuff,0,"PATH=%s","/local/sbin:/local/bin:/sbin:/bin") + 1;
if ((comspec = getenv("ComSpec")) || (comspec = getenv("COMSSPEC")))
envlen += snprintf(envbuff,0,"COMSPEC=%s",comspec) + 1;
if (envlen <= sizeof(envbuff)) {
envp = envptrs;
envstrs = envbuff;
} else if ((envstrs = calloc(envlen,1))) {
envp = envptrs;
} else {
return 0;
}
envp[0] = envstrs;
envstrs += sprintf(envstrs,"HOME=%s",pwd->pw_dir) + 1;
envp[1] = envstrs;
envstrs += sprintf(envstrs,"SHELL=%s",pwd->pw_shell) + 1;
envp[2] = envstrs;
envstrs += sprintf(envstrs,"TERM=%s","xterm") + 1;
envp[3] = envstrs;
envstrs += sprintf(envstrs,"LOGNAME=%s",pwd->pw_name) + 1;
envp[4] = envstrs;
envstrs += sprintf(envstrs,"USER=%s",pwd->pw_name) + 1;
envp[5] = envstrs;
envstrs += sprintf(envstrs,"PATH=%s","/local/sbin:/local/bin:/sbin:/bin") + 1;
envp[6] = 0;
envp[7] = 0;
if (comspec) {
envp[6] = envstrs;
envstrs += sprintf(envstrs,"COMSPEC=%s",comspec) + 1;
}
}
(void)signal(SIGTSTP, SIG_DFL);
(void)signal(SIGQUIT, SIG_DFL);
(void)signal(SIGINT, SIG_DFL);
motd();
execve(
pwd->pw_shell,
(char *[]){pwd->pw_shell,"-l",0},
envp);
return 0;
}
int main(int argc, char **argv)
{
struct passwd *pwd;
char *username = NULL;
int c, pflag, iflag = 0;
/* we don't want ^D etc to mess up the logic */
(void)signal(SIGTSTP, SIG_IGN);
(void)signal(SIGQUIT, SIG_IGN);
(void)signal(SIGINT, SIG_IGN);
while((c = getopt(argc, argv, "pfh:iw")) != -1)
switch(c) {
case 'p':
pflag = 1; break;
case 'f':
(void)0; break; /* unused, pointless currently */
case 'h':
if(getuid()) {
exit(1);
}
break;
case 'i':
iflag = IFLAG; break;
default:
case '?':
usage();
break;
}
argv += optind;
if(*argv)
username = *argv;
else {
printf("login: ");
fflush(0);
(void)scanf("%ms", &username);
}
pwd = getpwnam(username);
/* guard against account probing */
if(!pwd) {
char *pw = getpass("Password: ");
explicit_bzero(pw, strlen(pw));
endpwent();
puts("Login incorrect.");
return 1;
}
/* midipix: are we spawning a shell? */
if(!iflag) {
char *pw = getpass("Password: ");
/* TODO: shadow and locked account support */
if(!(*pwd->pw_passwd == '\0' && !strlen(pw))) {
char *pw_encrypted = crypt(pw, pwd->pw_passwd);
if(timingsafe_memcmp(pw_encrypted, pwd->pw_passwd, strlen(pw_encrypted)) != 0) {
puts("Login incorrect.");
explicit_bzero(pw, strlen(pw));
return 1;
}
explicit_bzero(pw, strlen(pw));
}
}
endpwent();
/* authenticated; attempt to set user context and spawn user shell */
if(switch_user_context(pwd, username) == 0) {
if(!do_login(pwd, pflag)) {
puts("failed to spawn shell.");
}
}
puts("could not switch to specified user.");
return 2;
}
void usage(void)
{
puts("login -p do not the destroy the environment");
puts("login -f do not perform secondary authentication (noop)");
puts("login -h pass remote server name to utmp (noop)");
exit(0);
}