sulogin: home cooked version, can be built -static

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/.gitignore

@@ -3,6 +3,7 @@ finit
 initctl
 logit
 reboot
+sulogin
 watchdogd
 Makefile
 Makefile.in

src/Makefile.am

@@ -8,10 +8,14 @@ AM_LDFLAGS         = -export-dynamic
 endif
 
 sbin_PROGRAMS        = finit initctl
-pkglibexec_PROGRAMS  =
+pkglibexec_PROGRAMS  = sulogin
 finit_pkglibdir      = $(pkglibdir)
 finit_pkglib_SCRIPTS = rescue.conf sample.conf
 
+sulogin_SOURCES      = sulogin.c
+sulogin_CFLAGS       = -W -Wall -Wextra -std=gnu99
+sulogin_LDADD        = -lcrypt
+
 if WATCHDOGD
 pkglibexec_PROGRAMS += watchdogd
 endif

src/sulogin.c

@@ -0,0 +1,186 @@
+/* poor man's sulogin, may be statically linked
+ *
+ * Copyright (c) 2021  Joachim Wiberg <troglobit@gmail.com>
+ *
+ * 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 <crypt.h>
+#include <err.h>
+#include <paths.h>
+#include <pwd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <termios.h>
+#include <unistd.h>
+
+/* getpwnam() cannot be used when statically linked */
+static int get_passwd(struct passwd *pw)
+{
+	char *ptr, *tmp;
+	char buf[256];
+	FILE *fp;
+
+	fp = fopen("/etc/passwd", "r");
+	if (!fp)
+		return 1;
+
+	while ((tmp = fgets(buf, sizeof(buf), fp))) {
+		if (!strstr(buf, ":0:0:"))
+			continue;	/* not uid 0 */
+
+		ptr = strsep(&tmp, ":");
+		if (!ptr)
+			break;
+		pw->pw_name = strdup(ptr);
+
+		ptr = strsep(&tmp, ":");
+		if (!ptr)
+			break;
+
+		if (strlen(ptr) > 1)
+			pw->pw_passwd = strdup(ptr);
+
+		break;			/* done, check it */
+	}
+	fclose(fp);
+
+	if (!pw->pw_name)
+		return 1;		/* no uid 0 here */
+	if (pw->pw_passwd)
+		return 0;		/* passwd in passwd */
+
+	fp = fopen("/etc/shadow", "r");
+	if (!fp) {
+		if (pw->pw_name)
+			free(pw->pw_name);
+		return 1;
+	}
+
+	while ((tmp = fgets(buf, sizeof(buf), fp))) {
+		ptr = strsep(&tmp, ":");
+		if (!ptr)
+			break;
+
+		if (!strcmp(tmp, pw->pw_name))
+			continue;
+
+		ptr = strsep(&tmp, ":");
+		if (!ptr)
+			break;
+
+		pw->pw_passwd = strdup(ptr);
+		break;
+	}
+	fclose(fp);
+
+	if (!pw->pw_passwd) {
+		if (pw->pw_name)
+			free(pw->pw_name);
+		return 1;		/* nopass => nologin */
+	}
+
+	return 0;			/* passwd in shadow */
+}
+
+static void freepw(struct passwd *pw)
+{
+	if (pw->pw_passwd) {
+		free(pw->pw_passwd);
+		pw->pw_passwd = NULL;
+	}
+	free(pw->pw_name);
+}
+
+int main(void)
+{
+	struct termios old, raw;
+	struct passwd pw = { 0 };
+
+	if (get_passwd(&pw))
+		err(1, "reading credentials for UID 0");
+
+	/* is login disabled, not much we can do */
+	if (strlen(pw.pw_passwd) == 1)
+		goto done;		/* likely one of: "x!*" */
+
+	if (tcgetattr(1, &old) < 0)
+		goto done;		/* failed reading tty */
+
+	raw = old;
+	raw.c_lflag &= ~ICANON;
+	raw.c_lflag &= ~ECHO;
+	raw.c_cc[VMIN] = 1;
+	raw.c_cc[VTIME] = 0;
+	if (tcsetattr(1, TCSANOW, &raw) < 0) {
+                tcsetattr(1, TCSANOW, &old);
+		goto done;		/* failed setting raw/pw mode */
+	}
+
+	while (1) {
+		char pwd[256];		/* reasonable max? */
+		size_t i = 0;
+		char *passwd;
+		char ch;
+
+		printf("Give %s password for maintenance: ", pw.pw_name);
+		do {
+			ch = getchar();
+			if (ch == EOF || ch == '\n' || ch == '\r')
+				break;
+			if (ch == 4)	/* Ctrl-D */
+				goto exit;
+
+			pwd[i++] = ch;
+		} while (i + 1 < sizeof(pwd));
+		pwd[i] = 0;
+		puts("");
+
+		passwd = crypt(pwd, pw.pw_passwd);
+		if (passwd && !strcmp(passwd, pw.pw_passwd)) {
+			char arg0[strlen(_PATH_BSHELL) + 2];
+			char *args[2] = {
+				arg0,
+				NULL
+			};
+
+			tcsetattr(1, TCSANOW, &old);	/* restore tty */
+			freepw(&pw);
+			snprintf(arg0, sizeof(arg0), "-%s", _PATH_BSHELL);
+			setenv("PS1", "# ", 1);
+
+			return execv(_PATH_BSHELL, args);
+		}
+	}
+
+exit:
+	tcsetattr(1, TCSANOW, &old);	/* restore tty */
+	puts("");
+done:
+	freepw(&pw);
+	return 1;
+}
+
+/**
+ * Local Variables:
+ *  indent-tabs-mode: t
+ *  c-file-style: "linux"
+ * End:
+ */