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Miller" , Jakub Kicinski , Neal Cardwell , Kuniyuki Iwashima , netdev@vger.kernel.org, kernel-team@cloudflare.com, Lee Valentine Subject: Re: [PATCH net-next v3 2/3] tcp: Consider every port when connecting with IP_LOCAL_PORT_RANGE In-Reply-To: <00911a84-c4e3-452e-ab51-1275a43ca4b2@redhat.com> (Paolo Abeni's message of "Thu, 17 Jul 2025 11:23:36 +0200") References: <20250714-connect-port-search-harder-v3-0-b1a41f249865@cloudflare.com> <20250714-connect-port-search-harder-v3-2-b1a41f249865@cloudflare.com> <00911a84-c4e3-452e-ab51-1275a43ca4b2@redhat.com> Date: Thu, 17 Jul 2025 11:44:01 +0200 Message-ID: <87qzyfdue6.fsf@cloudflare.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Thu, Jul 17, 2025 at 11:23 AM +02, Paolo Abeni wrote: > On 7/14/25 6:03 PM, Jakub Sitnicki wrote: >> Solution >> -------- >> >> If there is no IP address conflict with any socket bound to a given local >> port, then from the protocol's perspective, the port can be safely shared. >> >> With that in mind, modify the port search during connect(), that is >> __inet_hash_connect, to consider all bind buckets (ports) when looking for >> a local port for egress. >> >> To achieve this, add an extra walk over bhash2 buckets for the port to >> check for IP conflicts. The additional walk is not free, so perform it only >> once per port - during the second phase of conflict checking, when the >> bhash bucket is locked. >> >> We enable this changed behavior only if the IP_LOCAL_PORT_RANGE socket >> option is set. The rationale is that users are likely to care about using >> every possible local port only when they have deliberately constrained the >> ephemeral port range. > > I'm not a big fan of piggybacking additional semantic on existing > socketopt, have you considered a new one? That's a fair point. Though a dedicated sysctl seems more appropriate in this case. Akin to how we have ip_autobind_reuse to enable amore aggresive port sharing strategy on bind() side. How does that sound? > > At very least you will need to update the man page. > > >> diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c >> index d3ce6d0a514e..9d8a9c7c8274 100644 >> --- a/net/ipv4/inet_hashtables.c >> +++ b/net/ipv4/inet_hashtables.c >> @@ -1005,6 +1005,52 @@ EXPORT_IPV6_MOD(inet_bhash2_reset_saddr); >> #define INET_TABLE_PERTURB_SIZE (1 << CONFIG_INET_TABLE_PERTURB_ORDER) >> static u32 *table_perturb; >> >> +/* True on source address conflict with another socket. False otherwise. */ >> +static inline bool check_bind2_bucket(const struct sock *sk, >> + const struct inet_bind2_bucket *tb2) > > Please no inline function in c files. Will fix. Thanks for feedback.