last, fix race when comparing time stamps

It is just luck if two time() calls happen within the same
second. Introduced in 31d28e09.

Actually I don't like adding another global variable but this
way we avoid bigger refactoring. IMO it's questionable why
lastdate, lastdown, etc. are initialized with current time() at
all. It looks unsafe to print "still running" always when
logout_time = now.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>

diff --git a/login-utils/last.c b/login-utils/last.c
index 4a165c2c1b8cfe6734ae9a666cc8ae15ce29c9ef..8d82c106e27a412223461c9a9c7da811392c95b0 100644 (file)
--- a/login-utils/last.c
+++ b/login-utils/last.c
@@ -138,6 +138,7 @@ static struct last_timefmt timefmts[] = {
 /* Global variables */
 static unsigned int recsdone;  /* Number of records listed */
 static time_t lastdate;                /* Last date we've seen */
+static time_t currentdate;     /* date when we started processing the file */
 
 /* --time-format=option parser */
 static int which_time_format(const char *optarg)
@@ -372,7 +373,7 @@ static void trim_trailing_spaces(char *s)
  */
 static int list(const struct last_control *ctl, struct utmp *p, time_t logout_time, int what)
 {
-       time_t          secs, utmp_time, now;
+       time_t          secs, utmp_time;
        char            logintime[LAST_TIMESTAMP_LEN];
        char            logouttime[LAST_TIMESTAMP_LEN];
        char            length[LAST_TIMESTAMP_LEN];
@@ -428,8 +429,7 @@ static int list(const struct last_control *ctl, struct utmp *p, time_t logout_ti
        hours = (secs / 3600) % 24;
        days  = secs / 86400;
 
-       now = time(NULL);
-       if (logout_time == now) {
+       if (logout_time == currentdate) {
                if (ctl->time_fmt > LAST_TIMEFTM_SHORT_CTIME) {
                        sprintf(logouttime, "  still running");
                        length[0] = 0;
@@ -638,7 +638,7 @@ static void process_wtmp_file(const struct last_control *ctl,
        /*
         * Fill in 'lastdate'
         */
-       lastdate = lastrch = lastdown;
+       lastdate = currentdate = lastrch = lastdown;
 
        /*
         * Install signal handlers