netfilter: nf_tables: Introduce NFT_TABLE_F_PERSIST

This companion flag to NFT_TABLE_F_OWNER requests the kernel to keep the
table around after the process has exited. It marks such table as
orphaned (by dropping OWNER flag but keeping PERSIST flag in place),
which opens it for other processes to manipulate. For the sake of
simplicity, PERSIST flag may not be altered though.
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Florian Westphal <fw@strlen.de>

include/uapi/linux/netfilter/nf_tables.h

@@ -180,13 +180,16 @@ enum nft_hook_attributes {
  *
  * @NFT_TABLE_F_DORMANT: this table is not active
  * @NFT_TABLE_F_OWNER:   this table is owned by a process
+ * @NFT_TABLE_F_PERSIST: this table shall outlive its owner
  */
 enum nft_table_flags {
 	NFT_TABLE_F_DORMANT	= 0x1,
 	NFT_TABLE_F_OWNER	= 0x2,
+	NFT_TABLE_F_PERSIST	= 0x4,
 };
 #define NFT_TABLE_F_MASK	(NFT_TABLE_F_DORMANT | \
-				 NFT_TABLE_F_OWNER)
+				 NFT_TABLE_F_OWNER | \
+				 NFT_TABLE_F_PERSIST)
 
 /**
  * enum nft_table_attributes - nf_tables table netlink attributes

net/netfilter/nf_tables_api.c

@@ -1219,6 +1219,9 @@ static int nf_tables_updtable(struct nft_ctx *ctx)
 	     flags & NFT_TABLE_F_OWNER))
 		return -EOPNOTSUPP;
 
+	if ((flags ^ ctx->table->flags) & NFT_TABLE_F_PERSIST)
+		return -EOPNOTSUPP;
+
 	/* No dormant off/on/off/on games in single transaction */
 	if (ctx->table->flags & __NFT_TABLE_F_UPDATE)
 		return -EINVAL;
@@ -11345,6 +11348,10 @@ static int nft_rcv_nl_event(struct notifier_block *this, unsigned long event,
 	list_for_each_entry(table, &nft_net->tables, list) {
 		if (nft_table_has_owner(table) &&
 		    n->portid == table->nlpid) {
+			if (table->flags & NFT_TABLE_F_PERSIST) {
+				table->flags &= ~NFT_TABLE_F_OWNER;
+				continue;
+			}
 			__nft_release_hook(net, table);
 			list_del_rcu(&table->list);
 			to_delete[deleted++] = table;