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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: Phil Sutter , Simon Horman , netfilter-devel@vger.kernel.org, coreteam@netfilter.org, netdev@vger.kernel.org, Xiang Mei , Weiming Shi Subject: [PATCH v2] netfilter: nft_fwd_netdev: use recursion counter in neigh egress path Date: Thu, 9 Apr 2026 18:49:12 +0800 Message-ID: <20260409104911.722698-2-bestswngs@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit nft_fwd_neigh can be used in egress chains (NF_NETDEV_EGRESS). When the forwarding rule targets the same device or two devices forward to each other, neigh_xmit() triggers dev_queue_xmit() which re-enters nf_hook_egress(), causing infinite recursion and stack overflow. Move the nf_get_nf_dup_skb_recursion() accessor and NF_RECURSION_LIMIT to the shared header nf_dup_netdev.h as a static inline, so that nft_fwd_netdev can use the recursion counter directly without exported function call overhead. Guard neigh_xmit() with the same recursion limit already used in nf_do_netdev_egress(). Fixes: f87b9464d152 ("netfilter: nft_fwd_netdev: Support egress hook") Reported-by: Xiang Mei Signed-off-by: Weiming Shi --- include/net/netfilter/nf_dup_netdev.h | 13 +++++++++++++ net/netfilter/nf_dup_netdev.c | 16 ---------------- net/netfilter/nft_fwd_netdev.c | 7 +++++++ 3 files changed, 20 insertions(+), 16 deletions(-) diff --git a/include/net/netfilter/nf_dup_netdev.h b/include/net/netfilter/nf_dup_netdev.h index b175d271aec9..609bcf422a9b 100644 --- a/include/net/netfilter/nf_dup_netdev.h +++ b/include/net/netfilter/nf_dup_netdev.h @@ -3,10 +3,23 @@ #define _NF_DUP_NETDEV_H_ #include +#include +#include void nf_dup_netdev_egress(const struct nft_pktinfo *pkt, int oif); void nf_fwd_netdev_egress(const struct nft_pktinfo *pkt, int oif); +#define NF_RECURSION_LIMIT 2 + +static inline u8 *nf_get_nf_dup_skb_recursion(void) +{ +#ifndef CONFIG_PREEMPT_RT + return this_cpu_ptr(&softnet_data.xmit.nf_dup_skb_recursion); +#else + return ¤t->net_xmit.nf_dup_skb_recursion; +#endif +} + struct nft_offload_ctx; struct nft_flow_rule; diff --git a/net/netfilter/nf_dup_netdev.c b/net/netfilter/nf_dup_netdev.c index fab8b9011098..a958a1b0c5be 100644 --- a/net/netfilter/nf_dup_netdev.c +++ b/net/netfilter/nf_dup_netdev.c @@ -13,22 +13,6 @@ #include #include -#define NF_RECURSION_LIMIT 2 - -#ifndef CONFIG_PREEMPT_RT -static u8 *nf_get_nf_dup_skb_recursion(void) -{ - return this_cpu_ptr(&softnet_data.xmit.nf_dup_skb_recursion); -} -#else - -static u8 *nf_get_nf_dup_skb_recursion(void) -{ - return ¤t->net_xmit.nf_dup_skb_recursion; -} - -#endif - static void nf_do_netdev_egress(struct sk_buff *skb, struct net_device *dev, enum nf_dev_hooks hook) { diff --git a/net/netfilter/nft_fwd_netdev.c b/net/netfilter/nft_fwd_netdev.c index 152a9fb4d23a..492bb599a499 100644 --- a/net/netfilter/nft_fwd_netdev.c +++ b/net/netfilter/nft_fwd_netdev.c @@ -141,13 +141,20 @@ static void nft_fwd_neigh_eval(const struct nft_expr *expr, goto out; } + if (*nf_get_nf_dup_skb_recursion() > NF_RECURSION_LIMIT) { + verdict = NF_DROP; + goto out; + } + dev = dev_get_by_index_rcu(nft_net(pkt), oif); if (dev == NULL) return; skb->dev = dev; skb_clear_tstamp(skb); + (*nf_get_nf_dup_skb_recursion())++; neigh_xmit(neigh_table, dev, addr, skb); + (*nf_get_nf_dup_skb_recursion())--; out: regs->verdict.code = verdict; } -- 2.43.0