linux/include
Kuniyuki Iwashima 4b01a96742 tcp: bind(0) remove the SO_REUSEADDR restriction when ephemeral ports are exhausted.
Commit aacd9289af ("tcp: bind() use stronger
condition for bind_conflict") introduced a restriction to forbid to bind
SO_REUSEADDR enabled sockets to the same (addr, port) tuple in order to
assign ports dispersedly so that we can connect to the same remote host.

The change results in accelerating port depletion so that we fail to bind
sockets to the same local port even if we want to connect to the different
remote hosts.

You can reproduce this issue by following instructions below.

  1. # sysctl -w net.ipv4.ip_local_port_range="32768 32768"
  2. set SO_REUSEADDR to two sockets.
  3. bind two sockets to (localhost, 0) and the latter fails.

Therefore, when ephemeral ports are exhausted, bind(0) should fallback to
the legacy behaviour to enable the SO_REUSEADDR option and make it possible
to connect to different remote (addr, port) tuples.

This patch allows us to bind SO_REUSEADDR enabled sockets to the same
(addr, port) only when net.ipv4.ip_autobind_reuse is set 1 and all
ephemeral ports are exhausted. This also allows connect() and listen() to
share ports in the following way and may break some applications. So the
ip_autobind_reuse is 0 by default and disables the feature.

  1. setsockopt(sk1, SO_REUSEADDR)
  2. setsockopt(sk2, SO_REUSEADDR)
  3. bind(sk1, saddr, 0)
  4. bind(sk2, saddr, 0)
  5. connect(sk1, daddr)
  6. listen(sk2)

If it is set 1, we can fully utilize the 4-tuples, but we should use
IP_BIND_ADDRESS_NO_PORT for bind()+connect() as possible.

The notable thing is that if all sockets bound to the same port have
both SO_REUSEADDR and SO_REUSEPORT enabled, we can bind sockets to an
ephemeral port and also do listen().

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>
2020-03-12 12:08:09 -07:00
..
acpi ACPI: PM: s2idle: Check fixed wakeup events in acpi_s2idle_wake() 2020-02-21 10:01:25 -08:00
asm-generic
clocksource
crypto
drm
dt-bindings
keys
kunit
kvm
linux net: hns: reject unsupported coalescing params 2020-03-12 11:32:35 -07:00
math-emu
media
misc
net tcp: bind(0) remove the SO_REUSEADDR restriction when ephemeral ports are exhausted. 2020-03-12 12:08:09 -07:00
pcmcia
ras
rdma
scsi
soc net: dsa: felix: Allow unknown unicast traffic towards the CPU port module 2020-03-04 14:19:01 -08:00
sound
target
trace
uapi tcp: add bytes not sent to SCM_TIMESTAMPING_OPT_STATS 2020-03-09 17:56:33 -07:00
vdso
video
xen