kernel/linux.git/net/ipv4/udp.c, branch v6.3.2

inet: Add IP_LOCAL_PORT_RANGE socket option

2023-01-26T06:45:00+00:00

Users who want to share a single public IP address for outgoing connections between several hosts traditionally reach for SNAT. However, SNAT requires state keeping on the node(s) performing the NAT. A stateless alternative exists, where a single IP address used for egress can be shared between several hosts by partitioning the available ephemeral port range. In such a setup: 1. Each host gets assigned a disjoint range of ephemeral ports. 2. Applications open connections from the host-assigned port range. 3. Return traffic gets routed to the host based on both, the destination IP and the destination port. An application which wants to open an outgoing connection (connect) from a given port range today can choose between two solutions: 1. Manually pick the source port by bind()'ing to it before connect()'ing the socket. This approach has a couple of downsides: a) Search for a free port has to be implemented in the user-space. If the chosen 4-tuple happens to be busy, the application needs to retry from a different local port number. Detecting if 4-tuple is busy can be either easy (TCP) or hard (UDP). In TCP case, the application simply has to check if connect() returned an error (EADDRNOTAVAIL). That is assuming that the local port sharing was enabled (REUSEADDR) by all the sockets. # Assume desired local port range is 60_000-60_511 s = socket(AF_INET, SOCK_STREAM) s.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1) s.bind(("192.0.2.1", 60_000)) s.connect(("1.1.1.1", 53)) # Fails only if 192.0.2.1:60000 -> 1.1.1.1:53 is busy # Application must retry with another local port In case of UDP, the network stack allows binding more than one socket to the same 4-tuple, when local port sharing is enabled (REUSEADDR). Hence detecting the conflict is much harder and involves querying sock_diag and toggling the REUSEADDR flag [1]. b) For TCP, bind()-ing to a port within the ephemeral port range means that no connecting sockets, that is those which leave it to the network stack to find a free local port at connect() time, can use the this port. IOW, the bind hash bucket tb->fastreuse will be 0 or 1, and the port will be skipped during the free port search at connect() time. 2. Isolate the app in a dedicated netns and use the use the per-netns ip_local_port_range sysctl to adjust the ephemeral port range bounds. The per-netns setting affects all sockets, so this approach can be used only if: - there is just one egress IP address, or - the desired egress port range is the same for all egress IP addresses used by the application. For TCP, this approach avoids the downsides of (1). Free port search and 4-tuple conflict detection is done by the network stack: system("sysctl -w net.ipv4.ip_local_port_range='60000 60511'") s = socket(AF_INET, SOCK_STREAM) s.setsockopt(SOL_IP, IP_BIND_ADDRESS_NO_PORT, 1) s.bind(("192.0.2.1", 0)) s.connect(("1.1.1.1", 53)) # Fails if all 4-tuples 192.0.2.1:60000-60511 -> 1.1.1.1:53 are busy For UDP this approach has limited applicability. Setting the IP_BIND_ADDRESS_NO_PORT socket option does not result in local source port being shared with other connected UDP sockets. Hence relying on the network stack to find a free source port, limits the number of outgoing UDP flows from a single IP address down to the number of available ephemeral ports. To put it another way, partitioning the ephemeral port range between hosts using the existing Linux networking API is cumbersome. To address this use case, add a new socket option at the SOL_IP level, named IP_LOCAL_PORT_RANGE. The new option can be used to clamp down the ephemeral port range for each socket individually. The option can be used only to narrow down the per-netns local port range. If the per-socket range lies outside of the per-netns range, the latter takes precedence. UAPI-wise, the low and high range bounds are passed to the kernel as a pair of u16 values in host byte order packed into a u32. This avoids pointer passing. PORT_LO = 40_000 PORT_HI = 40_511 s = socket(AF_INET, SOCK_STREAM) v = struct.pack("I", PORT_HI << 16 | PORT_LO) s.setsockopt(SOL_IP, IP_LOCAL_PORT_RANGE, v) s.bind(("127.0.0.1", 0)) s.getsockname() # Local address between ("127.0.0.1", 40_000) and ("127.0.0.1", 40_511), # if there is a free port. EADDRINUSE otherwise. [1] https://github.com/cloudflare/cloudflare-blog/blob/232b432c1d57/2022-02-connectx/connectx.py#L116 Reviewed-by: Marek Majkowski Reviewed-by: Kuniyuki Iwashima Signed-off-by: Jakub Sitnicki Reviewed-by: Eric Dumazet Signed-off-by: Jakub Kicinski

net: Return errno in sk->sk_prot->get_port().

2022-11-21T13:05:39+00:00

We assume the correct errno is -EADDRINUSE when sk->sk_prot->get_port() fails, so some ->get_port() functions return just 1 on failure and the callers return -EADDRINUSE instead. However, mptcp_get_port() can return -EINVAL. Let's not ignore the error. Note the only exception is inet_autobind(), all of whose callers return -EAGAIN instead. Fixes: cec37a6e41aa ("mptcp: Handle MP_CAPABLE options for outgoing connections") Signed-off-by: Kuniyuki Iwashima Signed-off-by: David S. Miller

udp: Introduce optional per-netns hash table.

2022-11-16T09:43:35+00:00

The maximum hash table size is 64K due to the nature of the protocol. [0] It's smaller than TCP, and fewer sockets can cause a performance drop. On an EC2 c5.24xlarge instance (192 GiB memory), after running iperf3 in different netns, creating 32Mi sockets without data transfer in the root netns causes regression for the iperf3's connection. uhash_entries sockets length Gbps 64K 1 1 5.69 1Mi 16 5.27 2Mi 32 4.90 4Mi 64 4.09 8Mi 128 2.96 16Mi 256 2.06 32Mi 512 1.12 The per-netns hash table breaks the lengthy lists into shorter ones. It is useful on a multi-tenant system with thousands of netns. With smaller hash tables, we can look up sockets faster, isolate noisy neighbours, and reduce lock contention. The max size of the per-netns table is 64K as well. This is because the possible hash range by udp_hashfn() always fits in 64K within the same netns and we cannot make full use of the whole buckets larger than 64K. /* 0 < num < 64K -> X < hash < X + 64K */ (num + net_hash_mix(net)) & mask; Also, the min size is 128. We use a bitmap to search for an available port in udp_lib_get_port(). To keep the bitmap on the stack and not fire the CONFIG_FRAME_WARN error at build time, we round up the table size to 128. The sysctl usage is the same with TCP: $ dmesg | cut -d ' ' -f 6- | grep "UDP hash" UDP hash table entries: 65536 (order: 9, 2097152 bytes, vmalloc) # sysctl net.ipv4.udp_hash_entries net.ipv4.udp_hash_entries = 65536 # can be changed by uhash_entries # sysctl net.ipv4.udp_child_hash_entries net.ipv4.udp_child_hash_entries = 0 # disabled by default # ip netns add test1 # ip netns exec test1 sysctl net.ipv4.udp_hash_entries net.ipv4.udp_hash_entries = -65536 # share the global table # sysctl -w net.ipv4.udp_child_hash_entries=100 net.ipv4.udp_child_hash_entries = 100 # ip netns add test2 # ip netns exec test2 sysctl net.ipv4.udp_hash_entries net.ipv4.udp_hash_entries = 128 # own a per-netns table with 2^n buckets We could optimise the hash table lookup/iteration further by removing the netns comparison for the per-netns one in the future. Also, we could optimise the sparse udp_hslot layout by putting it in udp_table. [0]: https://lore.kernel.org/netdev/4ACC2815.7010101@gmail.com/ Signed-off-by: Kuniyuki Iwashima Signed-off-by: David S. Miller

udp: Access &udp_table via net.

2022-11-16T09:43:35+00:00

We will soon introduce an optional per-netns hash table for UDP. This means we cannot use udp_table directly in most places. Instead, access it via net->ipv4.udp_table. The access will be valid only while initialising udp_table itself and creating/destroying each netns. Signed-off-by: Kuniyuki Iwashima Signed-off-by: David S. Miller

udp: Set NULL to udp_seq_afinfo.udp_table.

2022-11-16T09:43:35+00:00

We will soon introduce an optional per-netns hash table for UDP. This means we cannot use the global udp_seq_afinfo.udp_table to fetch a UDP hash table. Instead, set NULL to udp_seq_afinfo.udp_table for UDP and get a proper table from net->ipv4.udp_table. Note that we still need udp_seq_afinfo.udp_table for UDP LITE. Signed-off-by: Kuniyuki Iwashima Signed-off-by: David S. Miller

udp: Set NULL to sk->sk_prot->h.udp_table.

2022-11-16T09:43:35+00:00

We will soon introduce an optional per-netns hash table for UDP. This means we cannot use the global sk->sk_prot->h.udp_table to fetch a UDP hash table. Instead, set NULL to sk->sk_prot->h.udp_table for UDP and get a proper table from net->ipv4.udp_table. Note that we still need sk->sk_prot->h.udp_table for UDP LITE. Signed-off-by: Kuniyuki Iwashima Signed-off-by: David S. Miller

udp: Clean up some functions.

2022-11-16T09:43:35+00:00

This patch adds no functional change and cleans up some functions that the following patches touch around so that we make them tidy and easy to review/revert. The change is mainly to keep reverse christmas tree order. Signed-off-by: Kuniyuki Iwashima Signed-off-by: David S. Miller

net: Change the udp encap_err_rcv to allow use of {ip,ipv6}_icmp_error()

2022-11-08T16:42:28+00:00

Change the udp encap_err_rcv signature to match ip_icmp_error() and ipv6_icmp_error() so that those can be used from the called function and export them. Signed-off-by: David Howells cc: Marc Dionne cc: linux-afs@lists.infradead.org cc: netdev@vger.kernel.org

Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net

2022-10-24T20:44:11+00:00

include/linux/net.h a5ef058dc4d9 ("net: introduce and use custom sockopt socket flag") e993ffe3da4b ("net: flag sockets supporting msghdr originated zerocopy") Signed-off-by: Jakub Kicinski

udp: track the forward memory release threshold in an hot cacheline

2022-10-24T09:52:50+00:00

When the receiver process and the BH runs on different cores, udp_rmem_release() experience a cache miss while accessing sk_rcvbuf, as the latter shares the same cacheline with sk_forward_alloc, written by the BH. With this patch, UDP tracks the rcvbuf value and its update via custom SOL_SOCKET socket options, and copies the forward memory threshold value used by udp_rmem_release() in a different cacheline, already accessed by the above function and uncontended. Since the UDP socket init operation grown a bit, factor out the common code between v4 and v6 in a shared helper. Overall the above give a 10% peek throughput increase under UDP flood. Signed-off-by: Paolo Abeni Reviewed-by: Eric Dumazet Acked-by: Kuniyuki Iwashima Signed-off-by: David S. Miller