On Mon, Nov 15, 2021 at 05:52:27PM +0100, Andrea Righi wrote:

There might be an arbitrary free open fd slot when we run the addfd
sub-test, so checking for progressive numbers of file descriptors
starting from memfd is not always a reliable check and we could get the
following failure:

  #  RUN           global.user_notification_addfd ...
  # seccomp_bpf.c:3989:user_notification_addfd:Expected listener (18) == nextfd++ (9)
  # user_notification_addfd: Test terminated by assertion

Simply check if memfd and listener are valid file descriptors and start
counting for progressive file checking with the listener fd.

Fixes: 93e720d710df ("selftests/seccomp: More closely track fds being assigned")
Signed-off-by: Andrea Righi <redacted>
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Thanks!
Acked-by: Christian Brauner <redacted>