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Wed, 13 May 2026 12:16:03 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id d++wD4NrBGo0FQAAD6G6ig (envelope-from ); Wed, 13 May 2026 12:16:03 +0000 From: Fernando Fernandez Mancera To: netfilter-devel@vger.kernel.org Cc: coreteam@netfilter.org, phil@nwl.cc, fw@strlen.de, pablo@netfilter.org, Fernando Fernandez Mancera , Alejandro Olivan Alvarez Subject: [PATCH nf] netfilter: nf_conncount: prevent connlimit drops for early confirmed ct Date: Wed, 13 May 2026 14:15:47 +0200 Message-ID: <20260513121547.6434-1-fmancera@suse.de> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: netfilter-devel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Spam-Flag: NO X-Spam-Score: -1.51 X-Rspamd-Action: no action X-Spamd-Result: default: False [-1.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_MISSING_CHARSET(0.50)[]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; TO_DN_SOME(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FREEMAIL_CC(0.00)[netfilter.org,nwl.cc,strlen.de,suse.de,gmail.com]; RCVD_TLS_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,suse.de:dkim,suse.de:mid,imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo]; TAGGED_RCPT(0.00)[]; RCPT_COUNT_SEVEN(0.00)[7]; DKIM_TRACE(0.00)[suse.de:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Rspamd-Queue-Id: B68DA5D2A8 X-Spam-Level: Commit 69894e5b4c5e ("netfilter: nft_connlimit: update the count if add was skipped") introduced a regression where packets for valid connections are dropped when using connlimit for soft-limiting scenarios. The issue occurs when a new connection reuses a socket currently in the TIME_WAIT state. In this scenario, the connection tracking entry is evaluated as already confirmed. Previously, __nf_conncount_add() assumed that if a connection was confirmed and did not originate from the loopback interface, it should skip the addition and return -EEXIST. Skipping the addition triggers a garbage collection run that cleans up the TIME_WAIT connection. Consequently, the active connection count drops to 0, which xt_connlimit mishandles, leading to the false rejection of the perfectly valid new connection. Fix this by replacing the interface check with protocol-agnostic state checks. We now skip the tree insertion and preserve the lockless garbage collection optimization only if the connection is IPS_ASSURED or IP_CT_ESTABLISHED. This allows early-confirmed setup packets (such as reused TIME_WAIT sockets or locally generated SYN-ACKs) to be properly evaluated and counted without falsely dropping. The goto check_connections path is maintained to ensure these setup packets are deduplicated correctly. This has been tested with slowhttptest and HTTP server configured locally to ensure we are not breaking soft-limiting scenarios for local or external connections. In addition, it was tested with a OVS zone limit too. Fixes: 69894e5b4c5e ("netfilter: nft_connlimit: update the count if add was skipped") Reported-by: Alejandro Olivan Alvarez Closes: https://lore.kernel.org/netfilter-devel/177349610461.3071718.4083978280323144323@eldamar.lan/ Signed-off-by: Fernando Fernandez Mancera --- net/netfilter/nf_conncount.c | 18 +++++++----------- 1 file changed, 7 insertions(+), 11 deletions(-) diff --git a/net/netfilter/nf_conncount.c b/net/netfilter/nf_conncount.c index 00eed5b4d1b1..bf718d26acda 100644 --- a/net/netfilter/nf_conncount.c +++ b/net/netfilter/nf_conncount.c @@ -129,13 +129,13 @@ static bool get_ct_or_tuple_from_skb(struct net *net, struct nf_conn **ct, struct nf_conntrack_tuple *tuple, const struct nf_conntrack_zone **zone, + enum ip_conntrack_info *ctinfo, bool *refcounted) { const struct nf_conntrack_tuple_hash *h; - enum ip_conntrack_info ctinfo; struct nf_conn *found_ct; - found_ct = nf_ct_get(skb, &ctinfo); + found_ct = nf_ct_get(skb, ctinfo); if (found_ct && !nf_ct_is_template(found_ct)) { *tuple = found_ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple; *zone = nf_ct_zone(found_ct); @@ -169,27 +169,22 @@ static int __nf_conncount_add(struct net *net, const struct nf_conntrack_tuple_hash *found; struct nf_conncount_tuple *conn, *conn_n; struct nf_conntrack_tuple tuple; + enum ip_conntrack_info ctinfo; struct nf_conn *ct = NULL; struct nf_conn *found_ct; unsigned int collect = 0; bool refcounted = false; int err = 0; - if (!get_ct_or_tuple_from_skb(net, skb, l3num, &ct, &tuple, &zone, &refcounted)) + if (!get_ct_or_tuple_from_skb(net, skb, l3num, &ct, &tuple, &zone, &ctinfo, &refcounted)) return -ENOENT; if (ct && nf_ct_is_confirmed(ct)) { - /* local connections are confirmed in postrouting so confirmation - * might have happened before hitting connlimit - */ - if (skb->skb_iif != LOOPBACK_IFINDEX) { + if (test_bit(IPS_ASSURED_BIT, &ct->status) || ctinfo == IP_CT_ESTABLISHED) { err = -EEXIST; goto out_put; } - /* this is likely a local connection, skip optimization to avoid - * adding duplicates from a 'packet train' - */ goto check_connections; } @@ -408,6 +403,7 @@ insert_tree(struct net *net, struct nf_conntrack_tuple tuple; struct nf_conncount_tuple *conn; struct nf_conncount_rb *rbconn; + enum ip_conntrack_info ctinfo; struct nf_conn *ct = NULL; spin_lock_bh(&nf_conncount_locks[hash]); @@ -451,7 +447,7 @@ insert_tree(struct net *net, goto restart; } - if (get_ct_or_tuple_from_skb(net, skb, l3num, &ct, &tuple, &zone, &refcounted)) { + if (get_ct_or_tuple_from_skb(net, skb, l3num, &ct, &tuple, &zone, &ctinfo, &refcounted)) { /* expected case: match, insert new node */ rbconn = kmem_cache_alloc(conncount_rb_cachep, GFP_ATOMIC); if (rbconn == NULL)