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[Martin Pitt <martin.pitt@xxxxxxxxxx>]

I tried to #undef __NR_socket in the systemd sources, to see where this
value is actually being used. Turns out it is in
https://github.com/systemd/systemd/blob/master/src/nspawn/nspawn.c#L1577
in setup_seccomp():

        r = seccomp_rule_add(
                        seccomp,
                        SCMP_ACT_ERRNO(EAFNOSUPPORT),
                        SCMP_SYS(socket),
                        2,
                        SCMP_A0(SCMP_CMP_EQ, AF_NETLINK),
                        SCMP_A2(SCMP_CMP_EQ, NETLINK_AUDIT));
        if (r < 0) {
                log_error_errno(r, "Failed to add audit seccomp rule: %m");


where SCMP_SYS is a macro from libseccomp-dev (/usr/include/seccomp.h):

/**
 * Convert a syscall name into the associated syscall number
 * @param x the syscall name
 */
#define SCMP_SYS(x)             (__NR_##x)

So this links the new syscall definition to seccomp. Apparently
seccomp_rule_add() (in the same seccomp.h file) behaves differently if
the syscall is defined. I just wonder how this actually built on i386
with the 4.2.0 kernel headers which did not have __NR_socket defined?

With current 4.3 kernel headers, the value of SCMP_SYS(socket) == 359,
as defined above. With the previous 4.2 kernel headers, the value is
4294967195 == 0xFFFFFF9B instead, apparently some auto-generated value.
So this explains how it built before.

So it looks like this might be between libseccomp and the kernel now?

-- 
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https://bugs.launchpad.net/bugs/1526358

Title:
  xenial/i386 regression: nspawn fails with "Failed to add audit seccomp
  rule: Bad address"

Status in linux package in Ubuntu:
  Confirmed
Status in systemd package in Ubuntu:
  Triaged

Bug description:
  Four days ago, on Dec 10,
  http://autopkgtest.ubuntu.com/packages/s/systemd/xenial/i386/ started
  failing:

  ======================================================================
  FAIL: test_boot (__main__.NspawnTest)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "/tmp/adt-run.IG1dKn/build.Yzd/systemd-228/debian/tests/boot-and-services", line 204, in test_boot
      self.assertIn(b'fake container started', out)
  AssertionError: b'fake container started' not found in b'Spawning container c1 on /tmp/tmpl04y_tf8/c1.\nPress ^] three times within 1s to kill container.\nFailed to create directory /tmp/tmpl04y_tf8/c1/sys/fs/selinux: Read-only file system\nFailed to create directory /tmp/tmpl04y_tf8/c1/sys/fs/selinux: Read-only file system\nFailed to add audit seccomp rule: Bad address\n'

  This is reproducible in xenial-release, i. e. it already slipped
  through -proposed.

  This can be reproduced easily on a xenial i386 VM:

    sudo apt-get install busybox-static
    mkdir -p /tmp/c/sbin /tmp/c/etc /tmp/c/bin/
    cp /bin/busybox /tmp/c/bin/
    ln -s ../bin/busybox /tmp/c/sbin/init
    ln -s busybox /tmp/c/bin/sh
    cp /etc/os-release /tmp/c/etc
    sudo systemd-nspawn -b -D /tmp/c

  This should normally boot a busybox container; you'll get a few error
  messages as there's no SysV init stuff there, but it should start and
  pressing enter should get you into a shell. But on i386 it fails with

  $   sudo systemd-nspawn -b -D /tmp/c
  Spawning container c on /tmp/c.
  Press ^] three times within 1s to kill container.
  Failed to create directory /tmp/c/sys/fs/selinux: Read-only file system
  Failed to create directory /tmp/c/sys/fs/selinux: Read-only file system
  Failed to add audit seccomp rule: Bad address

  which is what the test case fails on too.

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