signals: sys_ssetmask() uses uninitialized newmask

commit 5ba53ff6 upstream.

Commit 77097ae5 ("most of set_current_blocked() callers want
SIGKILL/SIGSTOP removed from set") removed the initialization of newmask
by accident, causing ltp to complain like this:

  ssetmask01    1  TFAIL  :  sgetmask() failed: TEST_ERRNO=???(0): Success

Restore the proper initialization.
Reported-and-tested-by: CAI Qian <caiqian@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

kernel/signal.c

@@ -3221,6 +3221,7 @@ SYSCALL_DEFINE1(ssetmask, int, newmask)
 	int old = current->blocked.sig[0];
 	sigset_t newset;
 
+	siginitset(&newset, newmask);
 	set_current_blocked(&newset);
 
 	return old;