libbb: split update_utmp from login/getty in preparation to use it for telnetd

function                                             old     new   delta
update_utent                                           -     339    +339
login_main                                          1498    1128    -370
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 0/1 up/down: 339/-370)          Total: -31 bytes

function                                             old     new   delta
update_utmp                                          246     337     +91
login_main                                          1128    1140     +12
getty_main                                          1908    1918     +10
...
update_utent                                         339       -    -339
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 5/6 up/down: 119/-368)         Total: -249 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

coreutils/who.c

@@ -16,7 +16,7 @@
  *
  *----------------------------------------------------------------------
  */
-/* BB_AUDIT SUSv3 _NOT_ compliant -- missing options -b, -d, -H, -l, -m, -p, -q, -r, -s, -t, -T, -u; Missing argument 'file'.  */
+/* BB_AUDIT SUSv3 _NOT_ compliant -- missing options -b, -d, -l, -m, -p, -q, -r, -s, -t, -T, -u; Missing argument 'file'.  */
 
 #include "libbb.h"
 #include <utmp.h>

include/libbb.h

@@ -796,6 +796,12 @@ void die_if_bad_username(const char* name) FAST_FUNC;
 #define die_if_bad_username(name) ((void)(name))
 #endif
 
+#if ENABLE_FEATURE_UTMP
+void FAST_FUNC update_utmp(int new_type, const char *short_tty, const char *username, const char *opt_host);
+#else
+# define update_utmp(new_type, short_tty, username, opt_host) ((void)0)
+#endif
+
 int execable_file(const char *name) FAST_FUNC;
 char *find_execable(const char *filename, char **PATHp) FAST_FUNC;
 int exists_execable(const char *filename) FAST_FUNC;

init/halt.c

@@ -30,7 +30,6 @@ static void write_wtmp(void)
 	if (uname(&uts) == 0)
 		safe_strncpy(utmp.ut_host, uts.release, sizeof(utmp.ut_host));
 	updwtmp(bb_path_wtmp_file, &utmp);
-
 }
 #else
 #define write_wtmp() ((void)0)

libbb/Kbuild

@@ -120,6 +120,8 @@ lib-y += xgethostbyname.o
 lib-y += xreadlink.o
 lib-y += xrealloc_vector.o
 
+lib-$(CONFIG_FEATURE_UTMP) += utmp.o
+
 # A mix of optimizations (why build stuff we know won't be used)
 # and objects which may fail to build (SELinux on selinux-less system)
 lib-$(CONFIG_SELINUX) += selinux_common.o

libbb/utmp.c

@@ -0,0 +1,92 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * utmp/wtmp support routines.
+ *
+ * Copyright (C) 2010 Denys Vlasenko
+ *
+ * Licensed under GPL version 2, see file LICENSE in this tarball for details.
+ */
+#include "libbb.h"
+#include <utmp.h>
+
+static void touch(const char *filename)
+{
+	if (access(filename, R_OK | W_OK) == -1)
+		close(open(filename, O_WRONLY | O_CREAT, 0664));
+}
+
+/*
+ * Read "man utmp" to make sense out of it.
+ */
+void FAST_FUNC update_utmp(int new_type, const char *short_tty, const char *username, const char *opt_host)
+{
+	struct utmp utent;
+	struct utmp *ut;
+	pid_t pid;
+
+	touch(_PATH_UTMP);
+	utmpname(_PATH_UTMP);
+	setutent();
+
+	pid = getpid();
+	/* Did init/getty/telnetd/sshd/... create an entry for us?
+	 * It should be (new_type-1), but we'd also reuse
+	 * any other potentially stale xxx_PROCESS entry */
+	while ((ut = getutent()) != NULL) {
+		if (ut->ut_pid == pid
+		// && ut->ut_line[0]
+		 && ut->ut_id[0] /* must have nonzero id */
+		 && (  ut->ut_type == INIT_PROCESS
+		    || ut->ut_type == LOGIN_PROCESS
+		    || ut->ut_type == USER_PROCESS
+		    || ut->ut_type == DEAD_PROCESS
+		    )
+		) {
+			utent = *ut; /* struct copy */
+			if (ut->ut_type >= new_type) {
+				/* Stale record. Nuke hostname */
+				memset(utent.ut_host, 0, sizeof(utent.ut_host));
+			}
+			/* NB: pututline (see later) searches for matching utent
+			 * using getutid(utent) - we must not change ut_id
+			 * if we want *exactly this* record to be overwritten!
+			 */
+			break;
+		}
+	}
+	endutent();
+
+	if (!ut) {
+		/* Didn't find anything, create new one */
+		memset(&utent, 0, sizeof(utent));
+		utent.ut_pid = pid;
+		/* Invent our own ut_id. ut_id is only 4 chars wide.
+		 * Try to fit something remotely meaningful... */
+		if (short_tty[0] == 'p') {
+			/* if "ptyXXX", map to "pXXX" */
+			/* if "pts/XX", map to "p/XX" */
+			utent.ut_id[0] = 'p';
+			strncpy(utent.ut_id + 1, short_tty + 3, sizeof(utent.ut_id)-1);
+		} else {
+			/* assuming it's "ttyXXXX", map to "XXXX" */
+			strncpy(utent.ut_id, short_tty + 3, sizeof(utent.ut_id));
+		}
+	}
+
+	utent.ut_type = new_type;
+	safe_strncpy(utent.ut_line, short_tty, sizeof(utent.ut_line));
+	safe_strncpy(utent.ut_user, username, sizeof(utent.ut_user));
+	if (opt_host)
+		safe_strncpy(utent.ut_host, opt_host, sizeof(utent.ut_host));
+	utent.ut_tv.tv_sec = time(NULL);
+
+	/* Update, or append new one */
+	setutent();
+	pututline(&utent);
+	endutent();
+
+#if ENABLE_FEATURE_WTMP
+	touch(bb_path_wtmp_file);
+	updwtmp(bb_path_wtmp_file, &utent);
+#endif
+}

loginutils/getty.c

@@ -19,7 +19,7 @@
 #include <syslog.h>
 
 #if ENABLE_FEATURE_UTMP
-#include <utmp.h> /* updwtmp() */
+#include <utmp.h> /* LOGIN_PROCESS */
 #endif
 
 #ifndef IUCLC
@@ -575,61 +575,6 @@ static void termios_final(struct options *op, struct termios *tp, struct chardat
 	ioctl_or_perror_and_die(0, TCSETS, tp, "%s: TCSETS", op->tty);
 }
 
-#if ENABLE_FEATURE_UTMP
-static void touch(const char *filename)
-{
-	if (access(filename, R_OK | W_OK) == -1)
-		close(open(filename, O_WRONLY | O_CREAT, 0664));
-}
-
-/* update_utmp - update our utmp entry */
-static NOINLINE void update_utmp(const char *line, char *fakehost)
-{
-	struct utmp ut;
-	struct utmp *utp;
-	int mypid = getpid();
-
-	/* In case we won't find an entry below... */
-	memset(&ut, 0, sizeof(ut));
-	safe_strncpy(ut.ut_id, line + 3, sizeof(ut.ut_id));
-
-	/*
-	 * The utmp file holds miscellaneous information about things started by
-	 * /sbin/init and other system-related events. Our purpose is to update
-	 * the utmp entry for the current process, in particular the process type
-	 * and the tty line we are listening to. Return successfully only if the
-	 * utmp file can be opened for update, and if we are able to find our
-	 * entry in the utmp file.
-	 */
-	touch(_PATH_UTMP);
-
-	utmpname(_PATH_UTMP);
-	setutent();
-	while ((utp = getutent()) != NULL) {
-		if (utp->ut_type == INIT_PROCESS && utp->ut_pid == mypid) {
-			memcpy(&ut, utp, sizeof(ut));
-			break;
-		}
-	}
-
-	strcpy(ut.ut_user, "LOGIN");
-	safe_strncpy(ut.ut_line, line, sizeof(ut.ut_line));
-	if (fakehost)
-		safe_strncpy(ut.ut_host, fakehost, sizeof(ut.ut_host));
-	ut.ut_tv.tv_sec = time(NULL);
-	ut.ut_type = LOGIN_PROCESS;
-	ut.ut_pid = mypid;
-
-	pututline(&ut);
-	endutent();
-
-#if ENABLE_FEATURE_WTMP
-	touch(bb_path_wtmp_file);
-	updwtmp(bb_path_wtmp_file, &ut);
-#endif
-}
-#endif /* CONFIG_FEATURE_UTMP */
-
 int getty_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int getty_main(int argc UNUSED_PARAM, char **argv)
 {
@@ -715,10 +660,8 @@ int getty_main(int argc UNUSED_PARAM, char **argv)
 	tcsetpgrp(0, getpid());
 #endif
 
-#if ENABLE_FEATURE_UTMP
 	/* Update the utmp file. This tty is ours now! */
-	update_utmp(options.tty, fakehost);
+	update_utmp(LOGIN_PROCESS, options.tty, "LOGIN", fakehost);
-#endif
 
 	/* Initialize the termios settings (raw mode, eight-bit, blocking i/o). */
 	debug("calling termios_init\n");

loginutils/login.c

@@ -2,25 +2,26 @@
 /*
  * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
  */
-
 #include "libbb.h"
 #include <syslog.h>
-#include <utmp.h>
+#if ENABLE_FEATURE_UTMP
+# include <utmp.h> /* USER_PROCESS */
+#endif
 #include <sys/resource.h>
 
 #if ENABLE_SELINUX
-#include <selinux/selinux.h>  /* for is_selinux_enabled()  */
+# include <selinux/selinux.h>  /* for is_selinux_enabled()  */
-#include <selinux/get_context_list.h> /* for get_default_context() */
+# include <selinux/get_context_list.h> /* for get_default_context() */
-#include <selinux/flask.h> /* for security class definitions  */
+# include <selinux/flask.h> /* for security class definitions  */
 #endif
 
 #if ENABLE_PAM
 /* PAM may include <locale.h>. We may need to undefine bbox's stub define: */
-#undef setlocale
+# undef setlocale
 /* For some obscure reason, PAM is not in pam/xxx, but in security/xxx.
  * Apparently they like to confuse people. */
-#include <security/pam_appl.h>
+# include <security/pam_appl.h>
-#include <security/pam_misc.h>
+# include <security/pam_misc.h>
 static const struct pam_conv conv = {
 	misc_conv,
 	NULL
@@ -36,87 +37,6 @@ enum {
 
 static char* short_tty;
 
-#if ENABLE_FEATURE_UTMP
-/* vv  Taken from tinylogin utmp.c  vv */
-/*
- * read_or_build_utent - see if utmp file is correct for this process
- *
- *	System V is very picky about the contents of the utmp file
- *	and requires that a slot for the current process exist.
- *	The utmp file is scanned for an entry with the same process
- *	ID.  If no entry exists the process exits with a message.
- *
- *	The "picky" flag is for network and other logins that may
- *	use special flags.  It allows the pid checks to be overridden.
- *	This means that getty should never invoke login with any
- *	command line flags.
- */
-
-static void read_or_build_utent(struct utmp *utptr, int run_by_root)
-{
-	struct utmp *ut;
-	pid_t pid = getpid();
-
-	setutent();
-
-	/* First, try to find a valid utmp entry for this process.  */
-	/* If there is one, just use it.  */
-	while ((ut = getutent()) != NULL) {
-		if (ut->ut_pid == pid && ut->ut_line[0] && ut->ut_id[0]
-		 && (ut->ut_type == LOGIN_PROCESS || ut->ut_type == USER_PROCESS)
-		) {
-			*utptr = *ut; /* struct copy */
-			if (run_by_root) /* why only for root? */
-				memset(utptr->ut_host, 0, sizeof(utptr->ut_host));
-			return;
-		}
-	}
-
-// Why? Do we require non-root to exec login from another
-// former login process (e.g. login shell)? Some login's have
-// login shells as children, so it won't work...
-//	if (!run_by_root)
-//		bb_error_msg_and_die("no utmp entry found");
-
-	/* Otherwise create a new one.  */
-	memset(utptr, 0, sizeof(*utptr));
-	utptr->ut_type = LOGIN_PROCESS;
-	utptr->ut_pid = pid;
-	strncpy(utptr->ut_line, short_tty, sizeof(utptr->ut_line));
-	/* This one is only 4 chars wide. Try to fit something
-	 * remotely meaningful by skipping "tty"... */
-	strncpy(utptr->ut_id, short_tty + 3, sizeof(utptr->ut_id));
-	strncpy(utptr->ut_user, "LOGIN", sizeof(utptr->ut_user));
-	utptr->ut_tv.tv_sec = time(NULL);
-}
-
-/*
- * write_utent - put a USER_PROCESS entry in the utmp file
- *
- *	write_utent changes the type of the current utmp entry to
- *	USER_PROCESS.  the wtmp file will be updated as well.
- */
-static void write_utent(struct utmp *utptr, const char *username)
-{
-	utptr->ut_type = USER_PROCESS;
-	strncpy(utptr->ut_user, username, sizeof(utptr->ut_user));
-	utptr->ut_tv.tv_sec = time(NULL);
-	/* other fields already filled in by read_or_build_utent above */
-	setutent();
-	pututline(utptr);
-	endutent();
-#if ENABLE_FEATURE_WTMP
-	if (access(bb_path_wtmp_file, R_OK|W_OK) == -1) {
-		close(creat(bb_path_wtmp_file, 0664));
-	}
-	updwtmp(bb_path_wtmp_file, utptr);
-#endif
-}
-#else /* !ENABLE_FEATURE_UTMP */
-#define read_or_build_utent(utptr, run_by_root) ((void)0)
-#define write_utent(utptr, username) ((void)0)
-#endif /* !ENABLE_FEATURE_UTMP */
-
 #if ENABLE_FEATURE_NOLOGIN
 static void die_if_nologin(void)
 {
@@ -144,7 +64,7 @@ static void die_if_nologin(void)
 	exit(EXIT_FAILURE);
 }
 #else
-static ALWAYS_INLINE void die_if_nologin(void) {}
+# define die_if_nologin() ((void)0)
 #endif
 
 #if ENABLE_FEATURE_SECURETTY && !ENABLE_PAM
@@ -286,11 +206,10 @@ int login_main(int argc UNUSED_PARAM, char **argv)
 	unsigned opt;
 	int count = 0;
 	struct passwd *pw;
-	char *opt_host = opt_host; /* for compiler */
+	char *opt_host = NULL;
 	char *opt_user = opt_user; /* for compiler */
 	char *full_tty;
 	IF_SELINUX(security_context_t user_sid = NULL;)
-	IF_FEATURE_UTMP(struct utmp utent;)
 #if ENABLE_PAM
 	int pamret;
 	pam_handle_t *pamh;
@@ -334,10 +253,7 @@ int login_main(int argc UNUSED_PARAM, char **argv)
 	if (strncmp(full_tty, "/dev/", 5) == 0)
 		short_tty += 5;
 
-	read_or_build_utent(&utent, run_by_root);
+	if (opt_host) {
-
-	if (opt & LOGIN_OPT_h) {
-		IF_FEATURE_UTMP(safe_strncpy(utent.ut_host, opt_host, sizeof(utent.ut_host));)
 		fromhost = xasprintf(" on '%s' from '%s'", short_tty, opt_host);
 	} else {
 		fromhost = xasprintf(" on '%s'", short_tty);
@@ -461,8 +377,6 @@ int login_main(int argc UNUSED_PARAM, char **argv)
 	if (pw->pw_uid != 0)
 		die_if_nologin();
 
-	write_utent(&utent, username);
-
 	IF_SELINUX(initselinux(username, full_tty, &user_sid));
 
 	/* Try these, but don't complain if they fail.
@@ -470,6 +384,8 @@ int login_main(int argc UNUSED_PARAM, char **argv)
 	fchown(0, pw->pw_uid, pw->pw_gid);
 	fchmod(0, 0600);
 
+	update_utmp(USER_PROCESS, short_tty, username, run_by_root ? opt_host : NULL);
+
 	/* We trust environment only if we run by root */
 	if (ENABLE_LOGIN_SCRIPTS && run_by_root)
 		run_login_script(pw, full_tty);