net: socket: Fix potential spectre v1 gadget in sock_is_registered

net: socket: Fix potential spectre v1 gadget in sock_is_registered

'family' can be a user-controlled value, so sanitize it after the bounds
check to avoid speculative out-of-bounds access.

Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jeremy Cline <jcline@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
CVE-2017-5753

(backported from commit e978de7a6d382ec378830ca2cf38e902df0b6d84)
[juergh: Adjusted for missing sock_is_registered().]
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>