selftests/net: Fix flaky bind_wildcard due to ephemeral port race

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bind_wildcard picks an ephemeral port by binding fd[0] with port 0, reads
it back with getsockname(), and then reuses that exact port number for the
other addresses/families in fd[1..7]. This all happens in the default
network namespace, so unrelated processes on the same host are drawing from
the very same ephemeral port range (net.ipv4.ip_local_port_range) at the
same time.

Such a process can independently get assigned that exact port number on a
different, non-conflicting address in the short window between fd[0]'s
bind() and fd[1]'s, making fd[1]'s bind() fail with EADDRINUSE for reasons
that have nothing to do with the wildcard-bind behavior under test, e.g.:

  # bind_wildcard.c:775:plain:Expected ret (-1) == 0 (0)
  # plain: Test terminated by assertion
  not ok N bind_wildcard.v6_local_v4_local.plain

Fix it the same way so_incoming_cpu.c, tcp_port_share.c and
reuseport_dualstack.c already do: unshare into a fresh network namespace
and bring lo up, so there is nobody else to race with for the port.

Signed-off-by: Ricardo B. Marlière (SUSE) <ricardo@marliere.net>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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Ricardo B. Marlière (SUSE) 2026-09-01 08:31:58 -03:00 • committed by Jakub Kicinski

parent 5cce5d2927

commit b910d4220d

1 changed files with 5 additions and 0 deletions

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tools/testing/selftests/net/bind_wildcard.c

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