{"id":2221279,"url":"http://patchwork.ozlabs.org/api/1.2/patches/2221279/?format=json","web_url":"http://patchwork.ozlabs.org/project/netfilter-devel/patch/20260409053629.698822-2-bestswngs@gmail.com/","project":{"id":26,"url":"http://patchwork.ozlabs.org/api/1.2/projects/26/?format=json","name":"Netfilter Development","link_name":"netfilter-devel","list_id":"netfilter-devel.vger.kernel.org","list_email":"netfilter-devel@vger.kernel.org","web_url":null,"scm_url":null,"webscm_url":null,"list_archive_url":"","list_archive_url_format":"","commit_url_format":""},"msgid":"<20260409053629.698822-2-bestswngs@gmail.com>","list_archive_url":null,"date":"2026-04-09T05:36:30","name":"[nf] netfilter: nft_fwd_netdev: use recursion counter in neigh egress path","commit_ref":null,"pull_url":null,"state":"changes-requested","archived":true,"hash":"34ab5a94b39d5a5fb7c6c05f3793d1201add954a","submitter":{"id":92941,"url":"http://patchwork.ozlabs.org/api/1.2/people/92941/?format=json","name":"Weiming Shi","email":"bestswngs@gmail.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/netfilter-devel/patch/20260409053629.698822-2-bestswngs@gmail.com/mbox/","series":[{"id":499237,"url":"http://patchwork.ozlabs.org/api/1.2/series/499237/?format=json","web_url":"http://patchwork.ozlabs.org/project/netfilter-devel/list/?series=499237","date":"2026-04-09T05:36:30","name":"[nf] netfilter: nft_fwd_netdev: use recursion counter in neigh egress path","version":1,"mbox":"http://patchwork.ozlabs.org/series/499237/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2221279/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2221279/checks/","tags":{},"related":[],"headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","netfilter-devel@vger.kernel.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256\n header.s=20251104 header.b=VxKuQp8K;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org\n (client-ip=172.234.253.10; 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Miller\" ,\n\tEric Dumazet ,\n\tJakub Kicinski ,\n\tPaolo Abeni ","Cc":"Phil Sutter ,\n\tSimon Horman ,\n\tnetfilter-devel@vger.kernel.org,\n\tcoreteam@netfilter.org,\n\tnetdev@vger.kernel.org,\n\tXiang Mei ,\n\tWeiming Shi ","Subject":"[PATCH nf] netfilter: nft_fwd_netdev: use recursion counter in neigh\n 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":"netfilter-devel@vger.kernel.org","List-Id":"","List-Subscribe":"","List-Unsubscribe":"","MIME-Version":"1.0","Content-Transfer-Encoding":"8bit"},"content":"nft_fwd_neigh_eval() can be attached to NF_NETDEV_EGRESS chains since\ncommit f87b9464d152 (\"netfilter: nft_fwd_netdev: Support egress hook\").\nWhen a forwarding rule targets the same device (or two devices forward\nto each other), the evaluator calls neigh_xmit() which reaches\ndev_queue_xmit(), re-entering nf_hook_egress() before the previous\ninvocation returns. This recurses until the kernel stack is exhausted.\n\nThe nf_dup_skb_recursion counter in nf_do_netdev_egress() was added by\ncommit fcd53c51d037 (\"netfilter: nf_dup_netdev: add and use recursion\ncounter\") to prevent exactly this class of bug, but nft_fwd_neigh_eval()\nbypasses that helper entirely by calling neigh_xmit() directly.\n\n BUG: KASAN: slab-out-of-bounds in nft_do_chain (net/netfilter/nf_tables_core.c:287)\n Call Trace:\n nft_do_chain (net/netfilter/nf_tables_core.c:287)\n nft_do_chain_netdev (net/netfilter/nft_chain_filter.c:289)\n nf_hook_slow (include/linux/netfilter.h:158)\n __dev_queue_xmit (net/core/dev.c:4807)\n neigh_resolve_output (include/linux/seqlock.h:392)\n neigh_xmit (net/core/neighbour.c:3230)\n nft_fwd_neigh_eval (net/netfilter/nft_fwd_netdev.c:150)\n nft_do_chain (net/netfilter/nf_tables_core.c:287)\n nft_do_chain_netdev (net/netfilter/nft_chain_filter.c:289)\n nf_hook_slow (include/linux/netfilter.h:158)\n __dev_queue_xmit (net/core/dev.c:4807)\n [repeats until stack exhaustion]\n\n Kernel panic - not syncing: Fatal exception in interrupt\n\nExport the recursion counter helpers from nf_dup_netdev and use them\nin nft_fwd_neigh_eval() to bound the recursion depth, matching the\nprotection already present in nf_do_netdev_egress().\n\nFixes: f87b9464d152 (\"netfilter: nft_fwd_netdev: Support egress hook\")\nReported-by: Xiang Mei \nSigned-off-by: Weiming Shi \n---\n include/net/netfilter/nf_dup_netdev.h | 4 ++++\n net/netfilter/nf_dup_netdev.c | 18 ++++++++++++++++++\n net/netfilter/nft_fwd_netdev.c | 7 +++++++\n 3 files changed, 29 insertions(+)","diff":"diff --git a/include/net/netfilter/nf_dup_netdev.h b/include/net/netfilter/nf_dup_netdev.h\nindex b175d271aec9..17362f76d1d1 100644\n--- a/include/net/netfilter/nf_dup_netdev.h\n+++ b/include/net/netfilter/nf_dup_netdev.h\n@@ -7,6 +7,10 @@\n void nf_dup_netdev_egress(const struct nft_pktinfo *pkt, int oif);\n void nf_fwd_netdev_egress(const struct nft_pktinfo *pkt, int oif);\n \n+bool nf_dup_netdev_has_recursed(void);\n+void nf_dup_netdev_recursion_inc(void);\n+void nf_dup_netdev_recursion_dec(void);\n+\n struct nft_offload_ctx;\n struct nft_flow_rule;\n \ndiff --git a/net/netfilter/nf_dup_netdev.c b/net/netfilter/nf_dup_netdev.c\nindex fab8b9011098..e2fe8bb6fe0d 100644\n--- a/net/netfilter/nf_dup_netdev.c\n+++ b/net/netfilter/nf_dup_netdev.c\n@@ -29,6 +29,24 @@ static u8 *nf_get_nf_dup_skb_recursion(void)\n \n #endif\n \n+bool nf_dup_netdev_has_recursed(void)\n+{\n+\treturn *nf_get_nf_dup_skb_recursion() > NF_RECURSION_LIMIT;\n+}\n+EXPORT_SYMBOL_GPL(nf_dup_netdev_has_recursed);\n+\n+void nf_dup_netdev_recursion_inc(void)\n+{\n+\t(*nf_get_nf_dup_skb_recursion())++;\n+}\n+EXPORT_SYMBOL_GPL(nf_dup_netdev_recursion_inc);\n+\n+void nf_dup_netdev_recursion_dec(void)\n+{\n+\t(*nf_get_nf_dup_skb_recursion())--;\n+}\n+EXPORT_SYMBOL_GPL(nf_dup_netdev_recursion_dec);\n+\n static void nf_do_netdev_egress(struct sk_buff *skb, struct net_device *dev,\n \t\t\t\tenum nf_dev_hooks hook)\n {\ndiff --git a/net/netfilter/nft_fwd_netdev.c b/net/netfilter/nft_fwd_netdev.c\nindex 152a9fb4d23a..d85f72af3589 100644\n--- a/net/netfilter/nft_fwd_netdev.c\n+++ b/net/netfilter/nft_fwd_netdev.c\n@@ -141,13 +141,20 @@ static void nft_fwd_neigh_eval(const struct nft_expr *expr,\n \t\tgoto out;\n \t}\n \n+\tif (nf_dup_netdev_has_recursed()) {\n+\t\tverdict = NF_DROP;\n+\t\tgoto out;\n+\t}\n+\n \tdev = dev_get_by_index_rcu(nft_net(pkt), oif);\n \tif (dev == NULL)\n \t\treturn;\n \n \tskb->dev = dev;\n \tskb_clear_tstamp(skb);\n+\tnf_dup_netdev_recursion_inc();\n \tneigh_xmit(neigh_table, dev, addr, skb);\n+\tnf_dup_netdev_recursion_dec();\n out:\n \tregs->verdict.code = verdict;\n }\n","prefixes":["nf"]}