login: fix /etc/nologin handling (should prohibit non-root LOGINS,

 not running login by non-root). minor code shrink.

function                                             old     new   delta
login_main                                          1669    1602     -67

1 files changed, 44 insertions, 36 deletions

diff --git a/loginutils/login.c b/loginutils/login.c
index 861382f12..70e3b1333 100644
--- a/loginutils/login.c
+++ b/loginutils/login.c
@@ -52,7 +52,7 @@ static char* short_tty;
  *      command line flags.
  */
 
-static void read_or_build_utent(struct utmp *utptr, int picky)
+static void read_or_build_utent(struct utmp *utptr, int run_by_root)
 {
         struct utmp *ut;
         pid_t pid = getpid();
@@ -60,30 +60,33 @@ static void read_or_build_utent(struct utmp *utptr, int picky)
         setutent();
 
         /* First, try to find a valid utmp entry for this process.  */
-        while ((ut = getutent()))
-                if (ut->ut_pid == pid && ut->ut_line[0] && ut->ut_id[0] &&
-                (ut->ut_type == LOGIN_PROCESS || ut->ut_type == USER_PROCESS))
-                        break;
+        /* 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;
+                }
 
-        /* If there is one, just use it, otherwise create a new one.  */
-        if (ut) {
-                *utptr = *ut;
-        } else {
-                if (picky)
-                        bb_error_msg_and_die("no utmp entry found");
-
-                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);
-        }
-        if (!picky)     /* root login */
-                memset(utptr->ut_host, 0, sizeof(utptr->ut_host));
+// 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);
 }
 
 /*
@@ -109,7 +112,7 @@ static void write_utent(struct utmp *utptr, const char *username)
 #endif
 }
 #else /* !ENABLE_FEATURE_UTMP */
-#define read_or_build_utent(utptr, picky) ((void)0)
+#define read_or_build_utent(utptr, run_by_root) ((void)0)
 #define write_utent(utptr, username) ((void)0)
 #endif /* !ENABLE_FEATURE_UTMP */
 
@@ -225,7 +228,7 @@ int login_main(int argc UNUSED_PARAM, char **argv)
         char *fromhost;
         char username[USERNAME_SIZE];
         const char *tmp;
-        int amroot;
+        int run_by_root;
         unsigned opt;
         int count = 0;
         struct passwd *pw;
@@ -248,8 +251,9 @@ int login_main(int argc UNUSED_PARAM, char **argv)
         signal(SIGALRM, alarm_handler);
         alarm(TIMEOUT);
 
-        /* More of suid paranoia if called by non-root */
-        amroot = !sanitize_env_if_suid(); /* Clear dangerous stuff, set PATH */
+        /* More of suid paranoia if called by non-root: */
+        /* Clear dangerous stuff, set PATH */
+        run_by_root = !sanitize_env_if_suid();
 
         /* Mandatory paranoia for suid applet:
          * ensure that fd# 0,1,2 are opened (at least to /dev/null)
@@ -259,7 +263,7 @@ int login_main(int argc UNUSED_PARAM, char **argv)
 
         opt = getopt32(argv, "f:h:p", &opt_user, &opt_host);
         if (opt & LOGIN_OPT_f) {
-                if (!amroot)
+                if (!run_by_root)
                         bb_error_msg_and_die("-f is for root only");
                 safe_strncpy(username, opt_user, sizeof(username));
         }
@@ -278,7 +282,7 @@ int login_main(int argc UNUSED_PARAM, char **argv)
                         short_tty = full_tty + 5;
         }
 
-        read_or_build_utent(&utent, !amroot);
+        read_or_build_utent(&utent, run_by_root);
 
         if (opt & LOGIN_OPT_h) {
                 USE_FEATURE_UTMP(
@@ -396,10 +400,12 @@ int login_main(int argc UNUSED_PARAM, char **argv)
                         return EXIT_FAILURE;
                 }
                 username[0] = '\0';
-        }
+        } /* while (1) */
 
         alarm(0);
-        if (!amroot)
+        /* We can ignore /etc/nologin if we are logging in as root,
+         * it doesn't matter whether we are run by root or not */
+        if (pw->pw_uid != 0)
                 die_if_nologin();
 
         write_utent(&utent, username);
@@ -433,7 +439,7 @@ int login_main(int argc UNUSED_PARAM, char **argv)
         fchmod(0, 0600);
 
         /* We trust environment only if we run by root */
-        if (ENABLE_LOGIN_SCRIPTS && amroot) {
+        if (ENABLE_LOGIN_SCRIPTS && run_by_root) {
                 char *t_argv[2];
 
                 t_argv[0] = getenv("LOGIN_PRE_SUID_SCRIPT");
@@ -479,14 +485,16 @@ int login_main(int argc UNUSED_PARAM, char **argv)
         // bb_setpgrp();
         // If this stuff is really needed, add it and explain why!
 
-        /* set signals to defaults */
-        signal(SIGALRM, SIG_DFL);
+        /* Set signals to defaults */
+        /*signal(SIGALRM, SIG_DFL); - not needed, we already set it
+         * to non-SIG_IGN, and on exec such signals are reset to SIG_DFL */
+
         /* Is this correct? This way user can ctrl-c out of /etc/profile,
          * potentially creating security breach (tested with bash 3.0).
          * But without this, bash 3.0 will not enable ctrl-c either.
          * Maybe bash is buggy?
          * Need to find out what standards say about /bin/login -
-         * should it leave SIGINT etc enabled or disabled? */
+         * should we leave SIGINT etc enabled or disabled? */
         signal(SIGINT, SIG_DFL);
 
         /* Exec login shell with no additional parameters */