Bug 1383921

Do you know for what is net_admin needed?

       CAP_NET_ADMIN
              Perform various network-related operations:
              * interface configuration;
              * administration of IP firewall, masquerading, and
                accounting;
              * modify routing tables;
              * bind to any address for transparent proxying;
              * set type-of-service (TOS)
              * clear driver statistics;
              * set promiscuous mode;
              * enabling multicasting;
              * use setsockopt(2) to set  the  following  socket
                options:  SO_DEBUG,  SO_MARK, SO_PRIORITY (for a
                priority outside the range 0 to  6),  SO_RCVBUF‐
                FORCE, and SO_SNDBUFFORCE.

Thanks to Noel Power (SUSE and Samba Team), we can now understand what has happened:

---------------------------
the net_admin DENIED error happens for smbd, winbind & nmb. This is related to
systemd and how samba communicates with it. Additionally that the operation is
denied is not a problem imho as the systemd code handles the EPERM gracefully.

Briefly all the samba daemons call 'become_daemon' (see
https://git.samba.org/?p=samba.git;a=blob;f=lib/util/become_daemon.c;h=9979fad569d993aa982d4074761a62f45cc6e95b;hb=HEAD#l66) The sd_notifyf in that function ends up calling fd_inc_sndbuf (see https://github.com/systemd/systemd/blob/master/src/libsystemd/sd-daemon/sd-daemon.c#L404 && https://github.com/systemd/systemd/blob/master/src/basic/socket-util.c#L754) and this results in the AVC.
---------------------------

https://github.com/systemd/systemd/blob/master/src/basic/socket-util.c#L754 is the following code in systemd:

----------------
int fd_inc_sndbuf(int fd, size_t n) {
        int r, value;
        socklen_t l = sizeof(value);

        r = getsockopt(fd, SOL_SOCKET, SO_SNDBUF, &value, &l);
        if (r >= 0 && l == sizeof(value) && (size_t) value >= n*2)
                return 0;

        /* If we have the privileges we will ignore the kernel limit. */

        value = (int) n;
        if (setsockopt(fd, SOL_SOCKET, SO_SNDBUFFORCE, &value, sizeof(value)) < 0)
                if (setsockopt(fd, SOL_SOCKET, SO_SNDBUF, &value, sizeof(value)) < 0)
                        return -errno;

        return 1;
}
---------------

All users of sd_notify will get this error. I think we can silence it in the case of Samba daemons, we don't really need values beyond the kernel limit.

Or the question is whether sd-daemon really needs 8MiB buffer
https://github.com/systemd/systemd/commit/a47806fafaec9a52a80e1795ad880b9b5008c4b8

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