The fallback flag in nsdispatch prevents the fallback implementation of

getgroupmembership() from invoking the correct backend in the compat case.
Replace it with a nesting depth counter so it only blocks one level (the
first is the group -> group_compat translation, the second is the actual
backend).  This is one of two bugs that break getgrouplist() in the compat
case, the second being that the backend's own getgroupmembership() method
is ignored.  Unfortunately, that is not easily fixable without a redesign
of our nss implementation (which is also needed to implement the +@group
syntax in /etc/passwd).

PR:		190055
MFC after:	1 week

1 files changed, 16 insertions, 9 deletions

diff --git a/lib/libc/net/nsdispatch.c b/lib/libc/net/nsdispatch.c
index c23315c..4de1df3 100644
--- a/lib/libc/net/nsdispatch.c
+++ b/lib/libc/net/nsdispatch.c
@@ -132,14 +132,17 @@ static	void			*nss_cache_cycle_prevention_func = NULL;
 #endif
 
 /*
- * When this is set to 1, nsdispatch won't use nsswitch.conf
- * but will consult the 'defaults' source list only.
- * NOTE: nested fallbacks (when nsdispatch calls fallback functions,
- *     which in turn calls nsdispatch, which should call fallback
- *     function) are not supported
+ * We keep track of nsdispatch() nesting depth in dispatch_depth.  When a
+ * fallback method is invoked from nsdispatch(), we temporarily set
+ * fallback_depth to the current dispatch depth plus one.  Subsequent
+ * calls at that exact depth will run in fallback mode (restricted to the
+ * same source as the call that was handled by the fallback method), while
+ * calls below that depth will be handled normally, allowing fallback
+ * methods to perform arbitrary lookups.
  */
 struct fb_state {
-	int	fb_dispatch;
+	int	dispatch_depth;
+	int	fallback_depth;
 };
 static	void	fb_endstate(void *);
 NSS_TLS_HANDLING(fb);
@@ -613,6 +616,7 @@ _nsdispatch(void *retval, const ns_dtab disp_tab[], const char *database,
 	void		*mdata;
 	int		 isthreaded, serrno, i, result, srclistsize;
 	struct fb_state	*st;
+	int		 saved_depth;
 
 #ifdef NS_CACHING
 	nss_cache_data	 cache_data;
@@ -644,7 +648,8 @@ _nsdispatch(void *retval, const ns_dtab disp_tab[], const char *database,
 		result = NS_UNAVAIL;
 		goto fin;
 	}
-	if (st->fb_dispatch == 0) {
+	++st->dispatch_depth;
+	if (st->dispatch_depth > st->fallback_depth) {
 		dbt = vector_search(&database, _nsmap, _nsmapsize, sizeof(*_nsmap),
 		    string_compare);
 		fb_method = nss_method_lookup(NSSRC_FALLBACK, database,
@@ -713,12 +718,13 @@ _nsdispatch(void *retval, const ns_dtab disp_tab[], const char *database,
 				break;
 		} else {
 			if (fb_method != NULL) {
-				st->fb_dispatch = 1;
+				saved_depth = st->fallback_depth;
+				st->fallback_depth = st->dispatch_depth + 1;
 				va_start(ap, defaults);
 				result = fb_method(retval,
 				    (void *)srclist[i].name, ap);
 				va_end(ap);
-				st->fb_dispatch = 0;
+				st->fallback_depth = saved_depth;
 			} else
 				nss_log(LOG_DEBUG, "%s, %s, %s, not found, "
 				    "and no fallback provided",
@@ -750,6 +756,7 @@ _nsdispatch(void *retval, const ns_dtab disp_tab[], const char *database,
 
 	if (isthreaded)
 		(void)_pthread_rwlock_unlock(&nss_lock);
+	--st->dispatch_depth;
 fin:
 	errno = serrno;
 	return (result);