systemd: add security fix

systemd: add security fix

Add a fix for CVE-2017-9445: In systemd through 233, certain sizes passed to
dns_packet_new in systemd-resolved can cause it to allocate a buffer that's
too small.  A malicious DNS server can exploit this via a response with a
specially crafted TCP payload to trick systemd-resolved into allocating a
buffer that's too small, and subsequently write arbitrary data beyond the
end of it.

The other patch fixes an issue with the security fix.

[Peter: use CVE description from MITRE]
Cc: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Cc: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>