af_key: Add lock to key dump

af_key: Add lock to key dump

BugLink: http://bugs.launchpad.net/bugs/1710646
commit 89e357d83c06b6fac581c3ca7f0ee3ae7e67109e upstream.

A dump may come in the middle of another dump, modifying its dump
structure members. This race condition will result in NULL pointer
dereference in kernel. So add a lock to prevent that race.

Fixes: 83321d6b9872 ("[AF_KEY]: Dump SA/SP entries non-atomically")
Signed-off-by: Yuejie Shi <syjcnss@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>