netfilter: nf_tables: Implement table adoption support

Allow a new process to take ownership of a previously owned table,
useful mostly for firewall management services restarting or suspending
when idle.

By extending __NFT_TABLE_F_UPDATE, the on/off/on check in
nf_tables_updtable() also covers table adoption, although it is actually
not needed: Table adoption is irreversible because nf_tables_updtable()
rejects attempts to drop NFT_TABLE_F_OWNER so table->nlpid setting can
happen just once within the transaction.

If the transaction commences, table's nlpid and flags fields are already
set and no further action is required. If it aborts, the table returns
to orphaned state.
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Florian Westphal <fw@strlen.de>

include/net/netfilter/nf_tables.h

@@ -1271,6 +1271,12 @@ static inline bool nft_table_has_owner(const struct nft_table *table)
 	return table->flags & NFT_TABLE_F_OWNER;
 }
 
+static inline bool nft_table_is_orphan(const struct nft_table *table)
+{
+	return (table->flags & (NFT_TABLE_F_OWNER | NFT_TABLE_F_PERSIST)) ==
+			NFT_TABLE_F_PERSIST;
+}
+
 static inline bool nft_base_chain_netdev(int family, u32 hooknum)
 {
 	return family == NFPROTO_NETDEV ||

net/netfilter/nf_tables_api.c

@@ -1194,8 +1194,10 @@ static void nf_tables_table_disable(struct net *net, struct nft_table *table)
 #define __NFT_TABLE_F_INTERNAL		(NFT_TABLE_F_MASK + 1)
 #define __NFT_TABLE_F_WAS_DORMANT	(__NFT_TABLE_F_INTERNAL << 0)
 #define __NFT_TABLE_F_WAS_AWAKEN	(__NFT_TABLE_F_INTERNAL << 1)
+#define __NFT_TABLE_F_WAS_ORPHAN	(__NFT_TABLE_F_INTERNAL << 2)
 #define __NFT_TABLE_F_UPDATE		(__NFT_TABLE_F_WAS_DORMANT | \
-					 __NFT_TABLE_F_WAS_AWAKEN)
+					 __NFT_TABLE_F_WAS_AWAKEN | \
+					 __NFT_TABLE_F_WAS_ORPHAN)
 
 static int nf_tables_updtable(struct nft_ctx *ctx)
 {
@@ -1215,8 +1217,8 @@ static int nf_tables_updtable(struct nft_ctx *ctx)
 
 	if ((nft_table_has_owner(ctx->table) &&
 	     !(flags & NFT_TABLE_F_OWNER)) ||
-	    (!nft_table_has_owner(ctx->table) &&
-	     flags & NFT_TABLE_F_OWNER))
+	    (flags & NFT_TABLE_F_OWNER &&
+	     !nft_table_is_orphan(ctx->table)))
 		return -EOPNOTSUPP;
 
 	if ((flags ^ ctx->table->flags) & NFT_TABLE_F_PERSIST)
@@ -1248,6 +1250,13 @@ static int nf_tables_updtable(struct nft_ctx *ctx)
 		}
 	}
 
+	if ((flags & NFT_TABLE_F_OWNER) &&
+	    !nft_table_has_owner(ctx->table)) {
+		ctx->table->nlpid = ctx->portid;
+		ctx->table->flags |= NFT_TABLE_F_OWNER |
+				     __NFT_TABLE_F_WAS_ORPHAN;
+	}
+
 	nft_trans_table_update(trans) = true;
 	nft_trans_commit_list_add_tail(ctx->net, trans);
 
@@ -10423,6 +10432,10 @@ static int __nf_tables_abort(struct net *net, enum nfnl_abort_action action)
 				} else if (trans->ctx.table->flags & __NFT_TABLE_F_WAS_AWAKEN) {
 					trans->ctx.table->flags &= ~NFT_TABLE_F_DORMANT;
 				}
+				if (trans->ctx.table->flags & __NFT_TABLE_F_WAS_ORPHAN) {
+					trans->ctx.table->flags &= ~NFT_TABLE_F_OWNER;
+					trans->ctx.table->nlpid = 0;
+				}
 				trans->ctx.table->flags &= ~__NFT_TABLE_F_UPDATE;
 				nft_trans_destroy(trans);
 			} else {