busybox/loginutils/passwd.c

/* vi: set sw=4 ts=4: */
/*
 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
 */

#include "busybox.h"
#include <syslog.h>


static void nuke_str(char *str)
{
	if (str) memset(str, 0, strlen(str));
}


static int i64c(int i)
{
	if (i <= 0)
		return '.';
	if (i == 1)
		return '/';
	if (i >= 2 && i < 12)
		return ('0' - 2 + i);
	if (i >= 12 && i < 38)
		return ('A' - 12 + i);
	if (i >= 38 && i < 63)
		return ('a' - 38 + i);
	return 'z';
}


static char *crypt_make_salt(void)
{
	time_t now;
	static unsigned long x;
	static char result[3];

	time(&now);
	x += now + getpid() + clock();
	result[0] = i64c(((x >> 18) ^ (x >> 6)) & 077);
	result[1] = i64c(((x >> 12) ^ x) & 077);
	result[2] = '\0';
	return result;
}


static char* new_password(const struct passwd *pw, const char *old_crypted,
			uid_t myuid, int algo)
{
	char salt[sizeof("$N$XXXXXXXX")]; /* "$N$XXXXXXXX" or "XX" */
	char *orig = "";
	char *newp = NULL;
	char *cipher = NULL;
	char *cp = NULL;
	char *ret = NULL; /* failure so far */

	if (myuid && old_crypted[0]) {
		orig = bb_askpass(0, "Old password:"); /* returns ptr to static */
		if (!orig)
			goto err_ret;
		cipher = pw_encrypt(orig, old_crypted); /* returns ptr to static */
		if (strcmp(cipher, old_crypted) != 0) {
			syslog(LOG_WARNING, "incorrect password for '%s'",
				pw->pw_name);
			bb_do_delay(FAIL_DELAY);
			puts("Incorrect password");
			goto err_ret;
		}
	}
	orig = xstrdup(orig); /* or else bb_askpass() will destroy it */
	newp = bb_askpass(0, "Enter the new password (minimum of 5 characters).\n"
	                   "Please use a combination of upper and lower case letters and numbers.\n"
	                   "Enter new password:"); /* returns ptr to static */
	if (!newp)
		goto err_ret;
	newp = xstrdup(newp); /* we are going to bb_askpass() again, so save it */
	if (obscure(orig, newp, pw)) {
		if (myuid)
			goto err_ret; /* non-root is not allowed to have weak passwd */
		puts("\nWarning: weak password (continuing)");
	}

	cp = bb_askpass(0, "Re-enter new password:");
	if (!cp)
		goto err_ret;
	if (strcmp(cp, newp)) {
		puts("Passwords do not match");
		goto err_ret;
	}

	memset(salt, 0, sizeof(salt));
	if (algo == 1) { /* MD5 */
		strcpy(salt, "$1$");
		strcat(salt, crypt_make_salt());
		strcat(salt, crypt_make_salt());
		strcat(salt, crypt_make_salt());
	}
	strcat(salt, crypt_make_salt());
	ret = xstrdup(pw_encrypt(newp, salt)); /* returns ptr to static */
	/* whee, success! */

 err_ret:
	nuke_str(orig);
	if (ENABLE_FEATURE_CLEAN_UP) free(orig);
	nuke_str(newp);
	if (ENABLE_FEATURE_CLEAN_UP) free(newp);
	nuke_str(cipher);
	nuke_str(cp);
	return ret;
}


static void set_filesize_limit(int blocks)
{
	struct rlimit rlimit_fsize;

	rlimit_fsize.rlim_cur = rlimit_fsize.rlim_max = 512L * blocks;
	setrlimit(RLIMIT_FSIZE, &rlimit_fsize);
}


#if 0
static int get_algo(char *a)
{
	/* standard: MD5 */
	int x = 1;
	if (strcasecmp(a, "des") == 0)
		x = 0;
	return x;
}
#endif


static int update_passwd(const char *filename, const char *username,
			const char *new_pw)
{
	struct stat sb;
	struct flock lock;
	FILE *old_fp;
	FILE *new_fp;
	char *new_name;
	char *last_char;
	unsigned user_len;
	int old_fd;
	int new_fd;
	int i;
	int ret = 1; /* failure */

	/* New passwd file, "/etc/passwd+" for now */
	new_name = xasprintf("%s+", filename);
	last_char = &new_name[strlen(new_name)-1];
	username = xasprintf("%s:", username);
	user_len = strlen(username);

	old_fp = fopen(filename, "r+");
	if (!old_fp)
		goto free_mem;
	old_fd = fileno(old_fp);

	/* Try to create "/etc/passwd+". Wait if it exists. */
	i = 30;
	do {
		// FIXME: on last iteration try w/o O_EXCL but with O_TRUNC?
		new_fd = open(new_name, O_WRONLY|O_CREAT|O_EXCL,0600);
		if (new_fd >= 0) goto created;
		if (errno != EEXIST) break;
		usleep(100000); /* 0.1 sec */
	} while (--i);
	bb_perror_msg("cannot create '%s'", new_name);
	goto close_old_fp;
 created:
	if (!fstat(old_fd, &sb)) {
		fchmod(new_fd, sb.st_mode & 0777); /* ignore errors */
		fchown(new_fd, sb.st_uid, sb.st_gid);
	}
	new_fp = fdopen(new_fd, "w");
	if (!new_fp) {
		close(new_fd);
		goto unlink_new;
	}

	/* Backup file is "/etc/passwd-" */
	last_char[0] = '-';
	/* Delete old one, create new as a hardlink to current */
	i = (unlink(new_name) && errno != ENOENT);
	if (i || link(filename, new_name))
		bb_perror_msg("warning: cannot create backup copy '%s'", new_name);
	last_char[0] = '+';

	/* Lock the password file before updating */
	lock.l_type = F_WRLCK;
	lock.l_whence = SEEK_SET;
	lock.l_start = 0;
	lock.l_len = 0;
	if (fcntl(old_fd, F_SETLK, &lock) < 0)
		bb_perror_msg("warning: cannot lock '%s'", filename);
	lock.l_type = F_UNLCK;

	/* Read current password file, write updated one */
	while (1) {
		char *line = xmalloc_fgets(old_fp);
		if (!line) break; /* EOF/error */
		if (strncmp(username, line, user_len) == 0) {
			/* we have a match with "username:"... */
			const char *cp = line + user_len;
			/* now cp -> old passwd, skip it: */
			cp = strchr(cp, ':');
			if (!cp) cp = "";
			/* now cp -> ':' after old passwd or -> "" */
			fprintf(new_fp, "%s%s%s", username, new_pw, cp);
			/* Erase password in memory */
		} else
			fputs(line, new_fp);
		free(line);
	}
	fcntl(old_fd, F_SETLK, &lock);

	/* We do want all of them to execute, thus | instead of || */
	if ((ferror(old_fp) | fflush(new_fp) | fsync(new_fd) | fclose(new_fp))
	 || rename(new_name, filename)
	) {
		/* At least one of those failed */
		goto unlink_new;
	}
	ret = 0; /* whee, success! */

 unlink_new:
	if (ret) unlink(new_name);

 close_old_fp:
	fclose(old_fp);

 free_mem:
	if (ENABLE_FEATURE_CLEAN_UP) free(new_name);
	if (ENABLE_FEATURE_CLEAN_UP) free((char*)username);
	return ret;
}


int passwd_main(int argc, char **argv)
{
	enum {
		OPT_algo = 0x1, /* -a - password algorithm */
		OPT_lock = 0x2, /* -l - lock account */
		OPT_unlock = 0x4, /* -u - unlock account */
		OPT_delete = 0x8, /* -d - delete password */
		OPT_lud = 0xe,
		STATE_ALGO_md5 = 0x10,
		STATE_ALGO_des = 0x20,
	};
	unsigned opt;
	char *opt_a = "";
	const char *filename;
	char *myname;
	char *name;
	char *oldp;
	char *newp = NULL; /* gcc happiness */
	const struct passwd *pw;
	uid_t myuid;

	openlog("passwd", LOG_NOWAIT, LOG_AUTH);
	opt = getopt32(argc, argv, "a:lud", &opt_a);
	argc -= optind;
	argv += optind;

	if (strcasecmp(opt_a, "des") == 0) /* -a */
		opt |= STATE_ALGO_des;
	else
		opt |= STATE_ALGO_md5;
	myuid = getuid();
	if ((opt & OPT_lud) && (!argc || myuid))
		bb_show_usage();

	myname = xstrdup(bb_getpwuid(NULL, myuid, -1));
	name = myname;
	if (argc) name = argv[0];

	pw = getpwnam(name);
	if (!pw) bb_error_msg_and_die("unknown user %s", name);
	if (myuid && pw->pw_uid != myuid) {
		syslog(LOG_WARNING, "can't change pwd for '%s'", name);
		bb_error_msg_and_die("permission denied");
	}

	filename = bb_path_passwd_file;
	oldp = pw->pw_passwd;
	if (ENABLE_FEATURE_SHADOWPASSWDS) {
		struct spwd *sp = getspnam(name);
		if (!sp) {
			bb_error_msg("no shadow record for user %s found, "
				"changing ordinary password instead", name);
		} else {
			filename = bb_path_shadow_file;
			oldp = sp->sp_pwdp;
		}
	}

	/* Decide what the new password will be */
	if (!(opt & OPT_lud)) {
		if (myuid) {
			if (oldp[0] == '!') {
				syslog(LOG_WARNING, "password locked for '%s'", name);
				bb_error_msg_and_die("the password for %s cannot be changed", name);
			}
		}
		printf("Changing password for %s\n", name);
		newp = new_password(pw, oldp,
					myuid,
					opt & STATE_ALGO_md5);
		if (!newp) {
			bb_error_msg_and_die("the password for %s is unchanged", name);
		}
	} else if (opt & OPT_lock) {
		if (oldp[0] == '!') goto skip;
		newp = xasprintf("!%s", oldp);
	} else if (opt & OPT_unlock) {
		if (oldp[0] != '!') goto skip;
		newp = xstrdup(oldp + 1);
	} else if (opt & OPT_delete) {
		newp = xstrdup("");
	}

	set_filesize_limit(30000);
	signal(SIGHUP, SIG_IGN);
	signal(SIGINT, SIG_IGN);
	signal(SIGQUIT, SIG_IGN);
	umask(077);
	xsetuid(0);
	if (update_passwd(filename, name, newp) == 0) {
		syslog(LOG_INFO, "password for '%s' changed by user '%s'", name,
				myname);
		puts("Password changed");
	} else {
		syslog(LOG_WARNING, "cannot update password file");
		bb_error_msg_and_die("cannot update password file");
	}

	if (ENABLE_FEATURE_CLEAN_UP) free(newp);
skip:
	if (ENABLE_FEATURE_CLEAN_UP) free(myname);
	return 0;
}