last: fix utmplist usage

last(1) uses a global list of entries, this is unnecessary and it's
also mistake because the pointer to the list is not set to NULL when
last(1) opens another utmp file. For example:

 last -f /var/log/wtmp -f /var/log/wtmp-20150220

ends with unexpected free() call or sometimes with never ending loop.

Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=1201033
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/login-utils/last.c b/login-utils/last.c
index d6d8d9624668ae591d9471a61111305d17fa8f0b..3d9a62bee2171d1b60ddf7b7e5a974c1395ec59f 100644 (file)
--- a/login-utils/last.c
+++ b/login-utils/last.c
@@ -107,7 +107,6 @@ struct utmplist {
        struct utmplist *next;
        struct utmplist *prev;
 };
-struct utmplist *utmplist = NULL;
 
 /* Types of listing */
 enum {
@@ -622,8 +621,10 @@ static int is_phantom(const struct last_control *ctl, struct utmp *ut)
 static void process_wtmp_file(const struct last_control *ctl)
 {
        FILE *fp;               /* Filepointer of wtmp file */
+       char *filename;
 
        struct utmp ut;         /* Current utmp entry */
+       struct utmplist *ulist = NULL;  /* All entries */
        struct utmplist *p;     /* Pointer into utmplist */
        struct utmplist *next;  /* Pointer into utmplist */
 
@@ -640,6 +641,7 @@ static void process_wtmp_file(const struct last_control *ctl)
 
        time(&lastdown);
        lastrch = lastdown;
+       filename = ctl->altv[ctl->alti];
 
        /*
         * Fill in 'lastdate'
@@ -655,8 +657,8 @@ static void process_wtmp_file(const struct last_control *ctl)
        /*
         * Open the utmp file
         */
-       if ((fp = fopen(ctl->altv[ctl->alti], "r")) == NULL)
-               err(EXIT_FAILURE, _("cannot open %s"), ctl->altv[ctl->alti]);
+       if ((fp = fopen(filename, "r")) == NULL)
+               err(EXIT_FAILURE, _("cannot open %s"), filename);
 
        /*
         * Optimize the buffer size.
@@ -670,7 +672,7 @@ static void process_wtmp_file(const struct last_control *ctl)
                begintime = ut.UL_UT_TIME;
        else {
                if (fstat(fileno(fp), &st) != 0)
-                       err(EXIT_FAILURE, _("stat of %s failed"), ctl->altv[ctl->alti]);
+                       err(EXIT_FAILURE, _("stat of %s failed"), filename);
                begintime = st.st_ctime;
                quit = 1;
        }
@@ -787,7 +789,7 @@ static void process_wtmp_file(const struct last_control *ctl)
                         * the same ut_line.
                         */
                        c = 0;
-                       for (p = utmplist; p; p = next) {
+                       for (p = ulist; p; p = next) {
                                next = p->next;
                                if (strncmp(p->ut.ut_line, ut.ut_line,
                                    UT_LINESIZE) == 0) {
@@ -796,11 +798,12 @@ static void process_wtmp_file(const struct last_control *ctl)
                                                quit = list(ctl, &ut, p->ut.UL_UT_TIME, R_NORMAL);
                                                c = 1;
                                        }
-                                       if (p->next) p->next->prev = p->prev;
+                                       if (p->next)
+                                               p->next->prev = p->prev;
                                        if (p->prev)
                                                p->prev->next = p->next;
                                        else
-                                               utmplist = p->next;
+                                               ulist = p->next;
                                        free(p);
                                }
                        }
@@ -829,10 +832,11 @@ static void process_wtmp_file(const struct last_control *ctl)
                                break;
                        p = xmalloc(sizeof(struct utmplist));
                        memcpy(&p->ut, &ut, sizeof(struct utmp));
-                       p->next  = utmplist;
+                       p->next  = ulist;
                        p->prev  = NULL;
-                       if (utmplist) utmplist->prev = p;
-                       utmplist = p;
+                       if (ulist)
+                               ulist->prev = p;
+                       ulist = p;
                        break;
 
                case EMPTY:
@@ -848,23 +852,24 @@ static void process_wtmp_file(const struct last_control *ctl)
 
                /*
                 * If we saw a shutdown/reboot record we can remove
-                * the entire current utmplist.
+                * the entire current ulist.
                 */
                if (down) {
                        lastboot = ut.UL_UT_TIME;
                        whydown = (ut.ut_type == SHUTDOWN_TIME) ? R_DOWN : R_CRASH;
-                       for (p = utmplist; p; p = next) {
+                       for (p = ulist; p; p = next) {
                                next = p->next;
                                free(p);
                        }
-                       utmplist = NULL;
+                       ulist = NULL;
                        down = 0;
                }
        }
 
-       printf(_("\n%s begins %s"), basename(ctl->altv[ctl->alti]), ctime(&begintime));
+       printf(_("\n%s begins %s"), basename(filename), ctime(&begintime));
        fclose(fp);
-       for (p = utmplist; p; p = next) {
+
+       for (p = ulist; p; p = next) {
                next = p->next;
                free(p);
        }
@@ -1001,7 +1006,7 @@ int main(int argc, char **argv)
                ctl.altc++;
        }
 
-       for (; ctl.alti < ctl.altc; ctl.alti++) {
+       for (ctl.alti = 0; ctl.alti < ctl.altc; ctl.alti++) {
                get_boot_time(&ctl.boot_time);
                process_wtmp_file(&ctl);
                free(ctl.altv[ctl.alti]);