https://bugs.gentoo.org/948106

Backport provided by Red Hat on the VINCE case.
diff --git a/flist.c b/flist.c
index 464d556..087f9da 100644
--- a/flist.c
+++ b/flist.c
@@ -2584,6 +2584,19 @@ struct file_list *recv_file_list(int f, int dir_ndx)
 		init_hard_links();
 #endif
 
+	if (inc_recurse && dir_ndx >= 0) {
+		if (dir_ndx >= dir_flist->used) {
+			rprintf(FERROR_XFER, "rsync: refusing invalid dir_ndx %u >= %u\n", dir_ndx, dir_flist->used);
+			exit_cleanup(RERR_PROTOCOL);
+		}
+		struct file_struct *file = dir_flist->files[dir_ndx];
+		if (file->flags & FLAG_GOT_DIR_FLIST) {
+			rprintf(FERROR_XFER, "rsync: refusing malicious duplicate flist for dir %d\n", dir_ndx);
+			exit_cleanup(RERR_PROTOCOL);
+		}
+		file->flags |= FLAG_GOT_DIR_FLIST;
+	}
+
 	flist = flist_new(0, "recv_file_list");
 	flist_expand(flist, FLIST_START_LARGE);
 
diff --git a/rsync.h b/rsync.h
index 0f9e277..b9a7101 100644
--- a/rsync.h
+++ b/rsync.h
@@ -84,6 +84,7 @@
 #define FLAG_DUPLICATE (1<<4)	/* sender */
 #define FLAG_MISSING_DIR (1<<4)	/* generator */
 #define FLAG_HLINKED (1<<5)	/* receiver/generator (checked on all types) */
+#define FLAG_GOT_DIR_FLIST (1<<5)/* sender/receiver/generator - dir_flist only */
 #define FLAG_HLINK_FIRST (1<<6)	/* receiver/generator (w/FLAG_HLINKED) */
 #define FLAG_IMPLIED_DIR (1<<6)	/* sender/receiver/generator (dirs only) */
 #define FLAG_HLINK_LAST (1<<7)	/* receiver/generator */