netfilter: nf_tables: fix chain dependency validation

The following ruleset:

 add table ip filter
 add chain ip filter input { type filter hook input priority 4; }
 add chain ip filter ap
 add rule ip filter input jump ap
 add rule ip filter ap masquerade

results in a panic, because the masquerade extension should be rejected
from the filter chain. The existing validation is missing a chain
dependency check when the rule is added to the non-base chain.

This patch fixes the problem by walking down the rules from the
basechains, searching for either immediate or lookup expressions, then
jumping to non-base chains and again walking down the rules to perform
the expression validation, so we make sure the full ruleset graph is
validated. This is done only once from the commit phase, in case of
problem, we abort the transaction and perform fine grain validation for
error reporting. This patch requires 003087911af2 ("netfilter:
nfnetlink: allow commit to fail") to achieve this behaviour.

This patch also adds a cleanup callback to nfnl batch interface to reset
the validate state from the exit path.

As a result of this patch, nf_tables_check_loops() doesn't use
->validate to check for loops, instead it just checks for immediate
expressions.

Reported-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

3 files changed, 11 insertions, 0 deletions

diff --git a/include/net/netfilter/nf_tables.h b/include/net/netfilter/nf_tables.h
index 6b9ddb9..435c32d 100644
--- a/include/net/netfilter/nf_tables.h
+++ b/include/net/netfilter/nf_tables.h
@@ -874,6 +874,8 @@ struct nft_chain {
 	struct nft_rule			**rules_next;
 };
 
+int nft_chain_validate(const struct nft_ctx *ctx, const struct nft_chain *chain);
+
 enum nft_chain_types {
 	NFT_CHAIN_T_DEFAULT = 0,
 	NFT_CHAIN_T_ROUTE,
diff --git a/include/net/netfilter/nf_tables_core.h b/include/net/netfilter/nf_tables_core.h
index cd6915b..e0c0c25 100644
--- a/include/net/netfilter/nf_tables_core.h
+++ b/include/net/netfilter/nf_tables_core.h
@@ -2,6 +2,8 @@
 #ifndef _NET_NF_TABLES_CORE_H
 #define _NET_NF_TABLES_CORE_H
 
+#include <net/netfilter/nf_tables.h>
+
 extern struct nft_expr_type nft_imm_type;
 extern struct nft_expr_type nft_cmp_type;
 extern struct nft_expr_type nft_lookup_type;
@@ -23,6 +25,12 @@ struct nft_cmp_fast_expr {
 	u8			len;
 };
 
+struct nft_immediate_expr {
+	struct nft_data		data;
+	enum nft_registers	dreg:8;
+	u8			dlen;
+};
+
 /* Calculate the mask for the nft_cmp_fast expression. On big endian the
  * mask needs to include the *upper* bytes when interpreting that data as
  * something smaller than the full u32, therefore a cpu_to_le32 is done.
diff --git a/include/net/netns/nftables.h b/include/net/netns/nftables.h
index 29c3851..94767ea 100644
--- a/include/net/netns/nftables.h
+++ b/include/net/netns/nftables.h
@@ -9,6 +9,7 @@ struct netns_nftables {
 	struct list_head	commit_list;
 	unsigned int		base_seq;
 	u8			gencursor;
+	u8			validate_state;
 };
 
 #endif