nft: cache: Review flush_cache()

While fixing for iptables-nft-restore under stress, I managed to hit
NULL-pointer deref in flush_cache(). Given that nftnl_*_list_free()
functions are not NULL-pointer tolerant, better make sure such are not
passed by accident.

Signed-off-by: Phil Sutter <phil@nwl.cc>

1 files changed, 11 insertions, 9 deletions

diff --git a/iptables/nft-cache.c b/iptables/nft-cache.c
index 0429fb32..0dd131e1 100644
--- a/iptables/nft-cache.c
+++ b/iptables/nft-cache.c
@@ -603,17 +603,19 @@ static int flush_cache(struct nft_handle *h, struct nft_cache *c,
 		if (h->tables[i].name == NULL)
 			continue;
 
-		if (!c->table[i].chains)
-			continue;
-
-		nftnl_chain_list_free(c->table[i].chains);
-		c->table[i].chains = NULL;
-		if (c->table[i].sets)
+		if (c->table[i].chains) {
+			nftnl_chain_list_free(c->table[i].chains);
+			c->table[i].chains = NULL;
+		}
+		if (c->table[i].sets) {
 			nftnl_set_list_free(c->table[i].sets);
-		c->table[i].sets = NULL;
+			c->table[i].sets = NULL;
+		}
+	}
+	if (c->tables) {
+		nftnl_table_list_free(c->tables);
+		c->tables = NULL;
 	}
-	nftnl_table_list_free(c->tables);
-	c->tables = NULL;
 
 	return 1;
 }