nbd_genl_status: null check for nla_nest_start

maillist inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8NC0E
CVE: CVE-2019-16089

Reference: https://lore.kernel.org/lkml/20190911164013.27364-1-navid.emamdoost@gmail.com/



---------------------------

nla_nest_start may fail and return NULL. The check is inserted, and
errno is selected based on other call sites within the same source code.
Update: removed extra new line.
v3 Update: added release reply, thanks to Michal Kubecek for pointing
out.

Signed-off-by: Navid Emamdoost <navid.emamdoost@gmail.com>
Reviewed-by: Michal Kubecek <mkubecek@suse.cz>