Add passwd(1).

login/login.8

@@ -65,6 +65,7 @@ textual interface is forced if this file exists
 exits 0 if the computer should power off, exits 1 if the computer should
 reboot, or exits 2 on fatal failure and the boot should halt.
 .Sh SEE ALSO
+.Xr passwd 1 ,
 .Xr crypt_checkpass 3 ,
 .Xr passwd 5 ,
 .Xr init 8 ,

utils/.gitignore

@@ -31,6 +31,7 @@ mkdir
 mktemp
 mv
 pager
+passwd
 ps
 pstree
 pwd

utils/Makefile

@@ -43,6 +43,7 @@ mkdir \
 mktemp \
 mv \
 pager \
+passwd \
 ps \
 pstree \
 pwd \

utils/passwd.cpp

@@ -0,0 +1,242 @@
+/*******************************************************************************
+
+    Copyright(C) Jonas 'Sortie' Termansen 2015.
+
+    This program is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by the Free
+    Software Foundation, either version 3 of the License, or (at your option)
+    any later version.
+
+    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, see <http://www.gnu.org/licenses/>.
+
+    passwd.cpp
+    Password change.
+
+*******************************************************************************/
+
+#include <sys/termmode.h>
+#include <sys/types.h>
+
+#include <err.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <pwd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <termios.h>
+#include <unistd.h>
+
+static void password(char* buffer,
+                     size_t buffer_size,
+                     const char* whose,
+                     const char* question)
+{
+	if ( !isatty(0) )
+		errx(1, "Input is not a terminal");
+	unsigned int termmode;
+	gettermmode(0, &termmode);
+	settermmode(0, termmode & ~TERMMODE_ECHO);
+	if ( whose )
+		printf("%s's ", whose);
+	printf("%s ", question);
+	fflush(stdout);
+	fflush(stdin);
+	// TODO: This may leave a copy of the password in the stdio buffer.
+	fgets(buffer, buffer_size, stdin);
+	fflush(stdin);
+	printf("\n");
+	size_t buffer_length = strlen(buffer);
+	if ( buffer_length && buffer[buffer_length-1] == '\n' )
+		buffer[--buffer_length] = '\0';
+	settermmode(0, termmode);
+}
+
+static void compact_arguments(int* argc, char*** argv)
+{
+	for ( int i = 0; i < *argc; i++ )
+	{
+		while ( i < *argc && !(*argv)[i] )
+		{
+			for ( int n = i; n < *argc; n++ )
+				(*argv)[n] = (*argv)[n+1];
+			(*argc)--;
+		}
+	}
+}
+
+static void version(FILE* fp, const char* argv0)
+{
+	fprintf(fp, "%s (Sortix) %s\n", argv0, VERSIONSTR);
+	fprintf(fp, "License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.\n");
+	fprintf(fp, "This is free software: you are free to change and redistribute it.\n");
+	fprintf(fp, "There is NO WARRANTY, to the extent permitted by law.\n");
+}
+
+static void help(FILE* fp, const char* argv0)
+{
+	fprintf(fp, "Usage: %s [OPTION]... [LOGIN]\n", argv0);
+}
+
+int main(int argc, char* argv[])
+{
+	const char* cipher = "blowfish,a";
+
+	const char* argv0 = argv[0];
+	for ( int i = 1; i < argc; i++ )
+	{
+		const char* arg = argv[i];
+		if ( arg[0] != '-' || !arg[1] )
+			continue;
+		argv[i] = NULL;
+		if ( !strcmp(arg, "--") )
+			break;
+		if ( arg[1] != '-' )
+		{
+			while ( char c = *++arg ) switch ( c )
+			{
+			case 'c':
+				if ( !*(cipher = arg + 1) )
+				{
+					if ( i + 1 == argc )
+					{
+						warnx("option requires an argument -- 'c'");
+						fprintf(stderr, "Try `%s --help' for more information.\n", argv[0]);
+						exit(125);
+					}
+					cipher = argv[i+1];
+					argv[++i] = NULL;
+				}
+				arg = "c";
+				break;
+			default:
+				fprintf(stderr, "%s: unknown option -- '%c'\n", argv0, c);
+				help(stderr, argv0);
+				exit(1);
+			}
+		}
+		else if ( !strcmp(arg, "--version") )
+			version(stdout, argv0), exit(0);
+		else if ( !strcmp(arg, "--help") )
+			help(stdout, argv0), exit(0);
+		else
+		{
+			fprintf(stderr, "%s: unrecognized option: %s\n", argv0, arg);
+			help(stderr, argv0);
+			exit(1);
+		}
+	}
+
+	compact_arguments(&argc, &argv);
+
+	uid_t my_uid = getuid();
+	char* my_username = getlogin();
+	if ( !my_username )
+		err(1, "failed to get username");
+	if ( !(my_username = strdup(my_username)) )
+		err(1, "stdup");
+
+	const char* username;
+	if ( argc <= 1 )
+		username = my_username;
+	else if ( argc <= 2 )
+		username = argv[1];
+	else
+		errx(1, "Unexpected extra operand");
+
+	errno = 0;
+	struct passwd* pwd = getpwnam(username);
+	if ( !pwd && errno == 0 )
+		errx(1, "%s: No such user", username);
+	if ( !pwd )
+		err(1, "%s", username);
+
+	if ( my_uid != 0 && pwd->pw_uid != my_uid )
+		errx(1, "You may not change the password for '%s'", username);
+
+	printf("Changing password for %s.\n", username);
+
+	if ( my_uid != 0 )
+	{
+		char current[128];
+		password(current, sizeof(current), pwd->pw_name,
+		         "current password (will not echo)");
+		if ( crypt_checkpass(current, pwd->pw_passwd) < 0 )
+			errx(1, "Wrong password for '%s'", pwd->pw_name);
+		explicit_bzero(current, sizeof(current));
+	}
+
+	char first[128];
+	password(first, sizeof(first), NULL, "Enter new password (will not echo)");
+	char second[128];
+	password(second, sizeof(second), NULL, "Enter new password (again)");
+	if ( strcmp(first, second) != 0 )
+		errx(1, "Passwords don't match");
+	explicit_bzero(second, sizeof(second));
+	char newhash[128];
+	if ( crypt_newhash(first, cipher, newhash, sizeof(newhash)) < 0 )
+		err(1, "crypt_newhash");
+	explicit_bzero(first, sizeof(first));
+
+	// TODO: This is subject to races and is obviously an insecure design.
+	//       The backend and coordination of the passwd database should be moved
+	//       to its own daemon.
+	int fd = open("/etc/passwd.new", O_WRONLY | O_CREAT | O_EXCL, 0644);
+	if ( fd < 0 )
+		err(1, "/etc/passwd.new");
+	fchown(fd, 0, 0); // HACK.
+	FILE* fp = fdopen(fd, "w");
+	if ( !fp )
+		err(1, "fdopen");
+	setpwent();
+	while ( (errno = 0, pwd = getpwent()) )
+	{
+		fputs(pwd->pw_name, fp);
+		fputc(':', fp);
+		if ( !strcmp(pwd->pw_name, username) )
+			fputs(newhash, fp);
+		else
+			fputs(pwd->pw_passwd, fp);
+		fputc(':', fp);
+		fprintf(fp, "%" PRIuUID, pwd->pw_uid);
+		fputc(':', fp);
+		fprintf(fp, "%" PRIuGID, pwd->pw_gid);
+		fputc(':', fp);
+		fputs(pwd->pw_gecos, fp);
+		fputc(':', fp);
+		fputs(pwd->pw_dir, fp);
+		fputc(':', fp);
+		fputs(pwd->pw_shell, fp);
+		fputc('\n', fp);
+		if ( ferror(fp) || fflush(stdout) == EOF )
+		{
+			unlink("/etc/passwd.new");
+			err(1, "/etc/passwd.new");
+		}
+	}
+	if ( errno != 0 )
+	{
+		unlink("/etc/passwd.new");
+		err(1, "getpwent");
+	}
+	if ( fclose(fp) == EOF )
+	{
+		unlink("/etc/passwd.new");
+		err(1, "/etc/passwd.new");
+	}
+	if ( rename("/etc/passwd.new", "/etc/passwd") < 0 )
+	{
+		unlink("/etc/passwd.new");
+		err(1, "rename: /etc/passwd.new -> /etc/passwd");
+	}
+
+	printf("Changed password for %s.\n", username);
+
+	return 0;
+}