From: Fernando Fernandez Mancera Connlimit expression can be used for all kind of packets and not only for packets with connection state new. See this ruleset as example: table ip filter { chain input { type filter hook input priority filter; policy accept; tcp dport 22 ct count over 4 counter } } Currently, if the connection count goes over the limit the counter will count the packets. When a connection is closed, the connection count won't decrement as it should because it is only updated for new connections due to an optimization on __nf_conncount_add() that prevents updating the list if the connection is duplicated. To solve this problem, check whether the connection was skipped and if so, update the list. Adjust count_tree() too so the same fix is applied for xt_connlimit. Fixes: 976afca1ceba ("netfilter: nf_conncount: Early exit in nf_conncount_lookup() and cleanup") Closes: https://lore.kernel.org/netfilter/trinity-85c72a88-d762-46c3-be97-36f10e5d9796-1761173693813@3c-app-mailcom-bs12/ Signed-off-by: Fernando Fernandez Mancera Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_conncount.c | 12 ++++++++---- net/netfilter/nft_connlimit.c | 13 +++++++++++-- 2 files changed, 19 insertions(+), 6 deletions(-) diff --git a/net/netfilter/nf_conncount.c b/net/netfilter/nf_conncount.c index eabce7e141f8..81915ef99a83 100644 --- a/net/netfilter/nf_conncount.c +++ b/net/netfilter/nf_conncount.c @@ -179,7 +179,7 @@ static int __nf_conncount_add(struct net *net, if (ct && nf_ct_is_confirmed(ct)) { if (refcounted) nf_ct_put(ct); - return 0; + return -EEXIST; } if ((u32)jiffies == list->last_gc) @@ -408,7 +408,7 @@ insert_tree(struct net *net, int ret; ret = nf_conncount_add_skb(net, skb, l3num, &rbconn->list); - if (ret) + if (ret && ret != -EEXIST) count = 0; /* hotdrop */ else count = rbconn->list.count; @@ -511,10 +511,14 @@ count_tree(struct net *net, /* same source network -> be counted! */ ret = __nf_conncount_add(net, skb, l3num, &rbconn->list); spin_unlock_bh(&rbconn->list.list_lock); - if (ret) + if (ret && ret != -EEXIST) { return 0; /* hotdrop */ - else + } else { + /* -EEXIST means add was skipped, update the list */ + if (ret == -EEXIST) + nf_conncount_gc_list(net, &rbconn->list); return rbconn->list.count; + } } } diff --git a/net/netfilter/nft_connlimit.c b/net/netfilter/nft_connlimit.c index 41770bde39d3..714a59485935 100644 --- a/net/netfilter/nft_connlimit.c +++ b/net/netfilter/nft_connlimit.c @@ -29,8 +29,17 @@ static inline void nft_connlimit_do_eval(struct nft_connlimit *priv, err = nf_conncount_add_skb(nft_net(pkt), pkt->skb, nft_pf(pkt), priv->list); if (err) { - regs->verdict.code = NF_DROP; - return; + if (err == -EEXIST) { + /* Call gc to update the list count if any connection has + * been closed already. This is useful for softlimit + * connections like limiting bandwidth based on a number + * of open connections. + */ + nf_conncount_gc_list(nft_net(pkt), priv->list); + } else { + regs->verdict.code = NF_DROP; + return; + } } count = READ_ONCE(priv->list->count); -- 2.47.3