[stat_cache] FAM: use entry hash index as userdata

Upon receipt of FAM event, validate that entry exists in splaytree
instead of blindly accessing memory through the pointer returned in
userdata by FAM

src/stat_cache.c

@@ -159,13 +159,15 @@ static handler_t stat_cache_handle_fdevent(server *srv, void *_fce, int revent)
 
 		for (i = 0; i < events; i++) {
 			FAMEvent fe;
-			fam_dir_entry *fam_dir;
 			splay_tree *node;
 			int ndx;
 
 			if (FAMNextEvent(&scf->fam, &fe) < 0) break;
-
-			/* handle event */
+			scf->dirs = splaytree_splay(scf->dirs, (int)(intptr_t)fe.userdata);
+			if (!scf->dirs || scf->dirs->key != (int)(intptr_t)fe.userdata) {
+				continue;
+			}
+			fam_dir_entry *fam_dir = scf->dirs->data;
 
 			switch(fe.code) {
 			case FAMChanged:
@@ -173,7 +175,6 @@ static handler_t stat_cache_handle_fdevent(server *srv, void *_fce, int revent)
 			case FAMMoved:
 				/* if the filename is a directory remove the entry */
 
-				fam_dir = fe.userdata;
 				fam_dir->version++;
 
 				/* file/dir is still here */
@@ -300,7 +301,7 @@ static void stat_cache_fam_dir_monitor(server *srv, stat_cache_fam *scf, stat_ca
 		fam_dir->version = 1;
 
 		if (0 != FAMMonitorDirectory(&scf->fam, fam_dir->name->ptr,
-					     &fam_dir->req, fam_dir)) {
+					     &fam_dir->req, (void *)(intptr_t)scf->dir_ndx)) {
 
 			log_error_write(srv, __FILE__, __LINE__, "sbsbs",
 					"monitoring dir failed:",