net: inet_diag: zero out uninitialized idiag_{src,dst} fields

Jakub reported while working with nlmon netlink sniffer that parts of
the inet_diag_sockid are not initialized when r->idiag_family != AF_INET6.
That is, fields of r->id.idiag_src[1 ... 3], r->id.idiag_dst[1 ... 3].

In fact, it seems that we can leak 6 * sizeof(u32) byte of kernel [slab]
memory through this. At least, in udp_dump_one(), we allocate a skb in ...

  rep = nlmsg_new(sizeof(struct inet_diag_msg) + ..., GFP_KERNEL);

... and then pass that to inet_sk_diag_fill() that puts the whole struct
inet_diag_msg into the skb, where we only fill out r->id.idiag_src[0],
r->id.idiag_dst[0] and leave the rest untouched:

  r->id.idiag_src[0] = inet->inet_rcv_saddr;
  r->id.idiag_dst[0] = inet->inet_daddr;

struct inet_diag_msg embeds struct inet_diag_sockid that is correctly /
fully filled out in IPv6 case, but for IPv4 not.

So just zero them out by using plain memset (for this little amount of
bytes it's probably not worth the extra check for idiag_family == AF_INET).

Similarly, fix also other places where we fill that out.

[Upstream commit b1aac815]

Change-Id: Ief40178e5bc9b4e9c207607e4c05970371d1e6f8
Reported-by: Jakub Zawadzki <darkjames-ws@darkjames.pl>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Lorenzo Colitti <lorenzo@google.com>