netdev - [PATCH net 3/3] netfilter: nf_tables: reject duplicate device on updates

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Message-ID: <20250813113800.20775-4-fw@strlen.de>
Date: Wed, 13 Aug 2025 13:36:38 +0200
From: Florian Westphal <fw@...len.de>
To: <netdev@...r.kernel.org>
Cc: Paolo Abeni <pabeni@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	<netfilter-devel@...r.kernel.org>,
	pablo@...filter.org
Subject: [PATCH net 3/3] netfilter: nf_tables: reject duplicate device on updates

From: Pablo Neira Ayuso <pablo@...filter.org>

A chain/flowtable update with duplicated devices in the same batch is
possible. Unfortunately, netdev event path only removes the first
device that is found, leaving unregistered the hook of the duplicated
device.

Check if a duplicated device exists in the transaction batch, bail out
with EEXIST in such case.

WARNING is hit when unregistering the hook:

 [49042.221275] WARNING: CPU: 4 PID: 8425 at net/netfilter/core.c:340 nf_hook_entry_head+0xaa/0x150
 [49042.221375] CPU: 4 UID: 0 PID: 8425 Comm: nft Tainted: G S                  6.16.0+ #170 PREEMPT(full)
 [...]
 [49042.221382] RIP: 0010:nf_hook_entry_head+0xaa/0x150

Fixes: 78d9f48f7f44 ("netfilter: nf_tables: add devices to existing flowtable")
Fixes: b9703ed44ffb ("netfilter: nf_tables: support for adding new devices to an existing netdev chain")
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
Signed-off-by: Florian Westphal <fw@...len.de>
---
 net/netfilter/nf_tables_api.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index 13d0ed9d1895..58c5425d61c2 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -2803,6 +2803,7 @@ static int nf_tables_updchain(struct nft_ctx *ctx, u8 genmask, u8 policy,
 	struct nft_chain *chain = ctx->chain;
 	struct nft_chain_hook hook = {};
 	struct nft_stats __percpu *stats = NULL;
+	struct nftables_pernet *nft_net;
 	struct nft_hook *h, *next;
 	struct nf_hook_ops *ops;
 	struct nft_trans *trans;
@@ -2845,6 +2846,20 @@ static int nf_tables_updchain(struct nft_ctx *ctx, u8 genmask, u8 policy,
 				if (nft_hook_list_find(&basechain->hook_list, h)) {
 					list_del(&h->list);
 					nft_netdev_hook_free(h);
+					continue;
+				}
+
+				nft_net = nft_pernet(ctx->net);
+				list_for_each_entry(trans, &nft_net->commit_list, list) {
+					if (trans->msg_type != NFT_MSG_NEWCHAIN ||
+					    trans->table != ctx->table ||
+					    !nft_trans_chain_update(trans))
+						continue;
+
+					if (nft_hook_list_find(&nft_trans_chain_hooks(trans), h)) {
+						nft_chain_release_hook(&hook);
+						return -EEXIST;
+					}
 				}
 			}
 		} else {
@@ -9060,6 +9075,7 @@ static int nft_flowtable_update(struct nft_ctx *ctx, const struct nlmsghdr *nlh,
 {
 	const struct nlattr * const *nla = ctx->nla;
 	struct nft_flowtable_hook flowtable_hook;
+	struct nftables_pernet *nft_net;
 	struct nft_hook *hook, *next;
 	struct nf_hook_ops *ops;
 	struct nft_trans *trans;
@@ -9076,6 +9092,20 @@ static int nft_flowtable_update(struct nft_ctx *ctx, const struct nlmsghdr *nlh,
 		if (nft_hook_list_find(&flowtable->hook_list, hook)) {
 			list_del(&hook->list);
 			nft_netdev_hook_free(hook);
+			continue;
+		}
+
+		nft_net = nft_pernet(ctx->net);
+		list_for_each_entry(trans, &nft_net->commit_list, list) {
+			if (trans->msg_type != NFT_MSG_NEWFLOWTABLE ||
+			    trans->table != ctx->table ||
+			    !nft_trans_flowtable_update(trans))
+				continue;
+
+			if (nft_hook_list_find(&nft_trans_flowtable_hooks(trans), hook)) {
+				err = -EEXIST;
+				goto err_flowtable_update_hook;
+			}
 		}
 	}
 
-- 
2.49.1