bug#65617: coreutils 9.4: seg.fault in readutmp with systemd

[Thorsten Kukuk]

coreutils 9.4 with the --enable-systemd option seg.faults in
lib/readutmp.c, line 801:

for (session_ptr = sessions; *session_ptr != NULL; session_ptr++)

If there is no session, "sessions" is NULL and "*session_ptr" will
dereference a NULL pointer.
Affected are who, pinky and uptime.

A simple fix:

diff --git a/lib/readutmp.c b/lib/readutmp.c
index 0173b7e0c1..e99158677c 100644
--- a/lib/readutmp.c
+++ b/lib/readutmp.c
@@ -795,7 +795,7 @@ read_utmp_from_systemd (idx_t *n_entries, STRUCT_UTMP 
**utmp_buf, int options)
     {
       char **sessions;
       int num_sessions = sd_get_sessions (&sessions);
-      if (num_sessions >= 0)
+      if (num_sessions > 0)
         {
           char **session_ptr;
           for (session_ptr = sessions; *session_ptr != NULL; session_ptr++)


-- 
Thorsten Kukuk, Distinguished Engineer, Senior Architect, Future Technologies
SUSE Software Solutions Germany GmbH, Frankenstraße 146, 90461 Nuernberg, 
Germany
Managing Director: Ivo Totev, Andrew McDonald, Werner Knoblich
(HRB 36809, AG Nürnberg)