netfilter: nf_tables: reject duplicate device on updates

JIRA: https://issues.redhat.com/browse/RHEL-115630
Upstream Status: commit cf5fb87

CS9 lacks
b9703ed ("netfilter: nf_tables: support for adding new devices to an existing netdev chain").
Associated hunks are discarded.

commit cf5fb87
Author: Pablo Neira Ayuso <pablo@netfilter.org>
Date:   Wed Aug 13 02:38:50 2025 +0200

    netfilter: nf_tables: reject duplicate device on updates

    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: 78d9f48 ("netfilter: nf_tables: add devices to existing flowtable")
    Fixes: b9703ed ("netfilter: nf_tables: support for adding new devices to an existing netdev chain")
    Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
    Signed-off-by: Florian Westphal <fw@strlen.de>

Signed-off-by: Florian Westphal <fwestpha@redhat.com>

Author: fw-strlen

net/netfilter/nf_tables_api.c

@@ -8211,6 +8211,7 @@ 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 nft_trans *trans;
 	bool unregister = false;
@@ -8226,6 +8227,20 @@ 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);
 			kfree(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->ctx.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;
+			}
 		}
 	}