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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 nf] netfilter: nft_fwd_netdev: use recursion counter in neigh egress path Date: Thu, 9 Apr 2026 13:36:30 +0800 Message-ID: <20260409053629.698822-2-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_eval() can be attached to NF_NETDEV_EGRESS chains since commit f87b9464d152 ("netfilter: nft_fwd_netdev: Support egress hook"). When a forwarding rule targets the same device (or two devices forward to each other), the evaluator calls neigh_xmit() which reaches dev_queue_xmit(), re-entering nf_hook_egress() before the previous invocation returns. This recurses until the kernel stack is exhausted. The nf_dup_skb_recursion counter in nf_do_netdev_egress() was added by commit fcd53c51d037 ("netfilter: nf_dup_netdev: add and use recursion counter") to prevent exactly this class of bug, but nft_fwd_neigh_eval() bypasses that helper entirely by calling neigh_xmit() directly. BUG: KASAN: slab-out-of-bounds in nft_do_chain (net/netfilter/nf_tables_core.c:287) Call Trace: nft_do_chain (net/netfilter/nf_tables_core.c:287) nft_do_chain_netdev (net/netfilter/nft_chain_filter.c:289) nf_hook_slow (include/linux/netfilter.h:158) __dev_queue_xmit (net/core/dev.c:4807) neigh_resolve_output (include/linux/seqlock.h:392) neigh_xmit (net/core/neighbour.c:3230) nft_fwd_neigh_eval (net/netfilter/nft_fwd_netdev.c:150) nft_do_chain (net/netfilter/nf_tables_core.c:287) nft_do_chain_netdev (net/netfilter/nft_chain_filter.c:289) nf_hook_slow (include/linux/netfilter.h:158) __dev_queue_xmit (net/core/dev.c:4807) [repeats until stack exhaustion] Kernel panic - not syncing: Fatal exception in interrupt Export the recursion counter helpers from nf_dup_netdev and use them in nft_fwd_neigh_eval() to bound the recursion depth, matching the protection already present 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 | 4 ++++ net/netfilter/nf_dup_netdev.c | 18 ++++++++++++++++++ net/netfilter/nft_fwd_netdev.c | 7 +++++++ 3 files changed, 29 insertions(+) diff --git a/include/net/netfilter/nf_dup_netdev.h b/include/net/netfilter/nf_dup_netdev.h index b175d271aec9..17362f76d1d1 100644 --- a/include/net/netfilter/nf_dup_netdev.h +++ b/include/net/netfilter/nf_dup_netdev.h @@ -7,6 +7,10 @@ void nf_dup_netdev_egress(const struct nft_pktinfo *pkt, int oif); void nf_fwd_netdev_egress(const struct nft_pktinfo *pkt, int oif); +bool nf_dup_netdev_has_recursed(void); +void nf_dup_netdev_recursion_inc(void); +void nf_dup_netdev_recursion_dec(void); + 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..e2fe8bb6fe0d 100644 --- a/net/netfilter/nf_dup_netdev.c +++ b/net/netfilter/nf_dup_netdev.c @@ -29,6 +29,24 @@ static u8 *nf_get_nf_dup_skb_recursion(void) #endif +bool nf_dup_netdev_has_recursed(void) +{ + return *nf_get_nf_dup_skb_recursion() > NF_RECURSION_LIMIT; +} +EXPORT_SYMBOL_GPL(nf_dup_netdev_has_recursed); + +void nf_dup_netdev_recursion_inc(void) +{ + (*nf_get_nf_dup_skb_recursion())++; +} +EXPORT_SYMBOL_GPL(nf_dup_netdev_recursion_inc); + +void nf_dup_netdev_recursion_dec(void) +{ + (*nf_get_nf_dup_skb_recursion())--; +} +EXPORT_SYMBOL_GPL(nf_dup_netdev_recursion_dec); + 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..d85f72af3589 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_dup_netdev_has_recursed()) { + 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_dup_netdev_recursion_inc(); neigh_xmit(neigh_table, dev, addr, skb); + nf_dup_netdev_recursion_dec(); out: regs->verdict.code = verdict; } -- 2.43.0