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. 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 --- v2: remove the ESTABLISHED check as it is redundant for the relevant protocols (UDP, TCP, SCTP). --- net/netfilter/nf_conncount.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/net/netfilter/nf_conncount.c b/net/netfilter/nf_conncount.c index 00eed5b4d1b1..facd7ffdf5c2 100644 --- a/net/netfilter/nf_conncount.c +++ b/net/netfilter/nf_conncount.c @@ -179,17 +179,16 @@ static int __nf_conncount_add(struct net *net, return -ENOENT; if (ct && nf_ct_is_confirmed(ct)) { - /* local connections are confirmed in postrouting so confirmation - * might have happened before hitting connlimit + /* Connection is confirmed but might still be in the setup phase. + * Only skip the tracking if it is fully assured. This guarantees + * that setup packets or retransmissions are properly counted and + * deduplicated. */ - if (skb->skb_iif != LOOPBACK_IFINDEX) { + if (test_bit(IPS_ASSURED_BIT, &ct->status)) { err = -EEXIST; goto out_put; } - /* this is likely a local connection, skip optimization to avoid - * adding duplicates from a 'packet train' - */ goto check_connections; } -- 2.53.0