fsck: Processes may kill other processes.

A error in disk-utils/fsck.c, if run the fsck -N command, processes
don't execute, just show what would be done. However, the pid whose
value is -1 is added to the instance_list list in the execute
function,if the kill_all function is called later, kill(-1, signum)
is executed, Signals are sent to all processes except the number one
process and itself. Other processes will be killed if they use the
default signal processing function.

Signed-off-by: zhanchengbin <zhanchengbin1@huawei.com>
Reviewed-by: Lukas Czerner <lczerner@redhat.com>

disk-utils/fsck.c

@@ -730,6 +730,8 @@ static int kill_all(int signum)
 	for (inst = instance_list; inst; inst = inst->next) {
 		if (inst->flags & FLAG_DONE)
 			continue;
+		if (inst->pid <= 0)
+			continue;
 		kill(inst->pid, signum);
 		n++;
 	}