login: fix potential null pointer dereference

Fix CID 1304686: Dereference after null check (FORWARD_NULL)

However, this commit does not fix any bug in logind. It helps to keep
the elect_display_compare() function generic.

diff --git a/src/login/logind-user.c b/src/login/logind-user.c
index c0b473930db0bf71e69861de2e60ec5b552c2a39..a9cf529e12a049899e46a10f32f99a584b3bad4a 100644 (file)
--- a/src/login/logind-user.c
+++ b/src/login/logind-user.c
@@ -763,6 +763,9 @@ static int elect_display_compare(Session *s1, Session *s2) {
          * is preferred.
          *
          * s1 or s2 may be NULL. */
+        if (!s1 && !s2)
+                return 0;
+
         if ((s1 == NULL) != (s2 == NULL))
                 return (s1 == NULL) - (s2 == NULL);