nsswitch: handle missing actions properly

[DJ Delorie]

RCA: the __nss_database_get return value is nonzero on ERROR, not on
MISSING.  A separate check for MISSING is needed.  This only really
affects initgroups, since it has a fallback, so needs to know if
initgroups is missing from nsswitch.conf.  Note: it's now possible to
have a line in nsswitch.conf like this:

initgroups:

That is *not* MISSING but has an empty module list.  If this is
undesired behavior, a further "&& nip->module" is needed.  The
nss_database.c patch ensures an empty module list for an empty
nsswitch.conf list, instead of 

See also https://bugzilla.redhat.com/show_bug.cgi?id=1906066

Actual proposed commit follows:

-----
Some internal functions need to know if a database has a nonzero
list of actions; success getting the database does not guarantee
that.  Add checks for such as needed.

Skip the ":" in each nsswitch.conf line so as not to add a dummy
action libnss_:.so

diff --git a/grp/initgroups.c b/grp/initgroups.c
index a60ca1c395..a0a836d862 100644
--- a/grp/initgroups.c
+++ b/grp/initgroups.c
@@ -72,11 +72,13 @@ internal_getgrouplist (const char *user, gid_t group, long int *size,
 
   nss_action_list nip;
 
-  if (__nss_database_get (nss_database_initgroups, &nip))
+  if (__nss_database_get (nss_database_initgroups, &nip)
+      && nip != NULL)
     {
       use_initgroups_entry = true;
     }
-  else if (__nss_database_get (nss_database_group, &nip))
+  else if (__nss_database_get (nss_database_group, &nip)
+      && nip != NULL)
     {
       use_initgroups_entry = false;
     }
diff --git a/nss/nss_database.c b/nss/nss_database.c
index e8c307d1f3..a036e95fbf 100644
--- a/nss/nss_database.c
+++ b/nss/nss_database.c
@@ -212,7 +212,8 @@ process_line (struct nss_database_data *data, char *line)
   if (line[0] == '\0' || name == line)
     /* Syntax error.  Skip this line.  */
     return true;
-  *line++ = '\0';
+  while (line[0] != '\0' && (isspace (line[0]) || line[0] == ':'))
+    *line++ = '\0';
 
   int db = name_to_database_index (name);
   if (db < 0)
diff --git a/nss/nsswitch.c b/nss/nsswitch.c
index 40109c744d..921062e04f 100644
--- a/nss/nsswitch.c
+++ b/nss/nsswitch.c
@@ -81,7 +81,7 @@ __nss_database_lookup2 (const char *database, const char *alternate_name,
   if (database_names[database_id] == NULL)
     return -1;
 
-  if (__nss_database_get (database_id, ni))
+  if (__nss_database_get (database_id, ni) && *ni)
     {
       /* Success.  */
       return 0;