exec: Copy oldsighand->action under spin-lock

exec: Copy oldsighand->action under spin-lock

commit 5bf2fedca8f59379025b0d52f917b9ddb9bfe17e upstream.

unshare_sighand should only access oldsighand->action
while holding oldsighand->siglock, to make sure that
newsighand->action is in a consistent state.

Signed-off-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
Cc: stable@vger.kernel.org
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/AM8PR10MB470871DEBD1DED081F9CC391E4389@AM8PR10MB4708.EURPRD10.PROD.OUTLOOK.COM
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>