exec: don't turn PF_KTHREAD off when a target command was not found

Presently do_execve() turns PF_KTHREAD off before search_binary_handler().
 THis has a theorical risk of PF_KTHREAD getting lost.  We don't have to
turn PF_KTHREAD off in the ENOEXEC case.

This patch moves this flag modification to after the finding of the
executable file.

This is only a theorical issue because kthreads do not call do_execve()
directly.  But fixing would be better.
Signed-off-by: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: NRoland McGrath <roland@redhat.com>
Acked-by: NOleg Nesterov <oleg@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/exec.c

@@ -1009,7 +1009,7 @@ int flush_old_exec(struct linux_binprm * bprm)
 
 	bprm->mm = NULL;		/* We're using it now */
 
-	current->flags &= ~PF_RANDOMIZE;
+	current->flags &= ~(PF_RANDOMIZE | PF_KTHREAD);
 	flush_thread();
 	current->personality &= ~bprm->per_clear;
 
@@ -1412,7 +1412,6 @@ int do_execve(const char * filename,
 	if (retval < 0)
 		goto out;
 
-	current->flags &= ~PF_KTHREAD;
 	retval = search_binary_handler(bprm,regs);
 	if (retval < 0)
 		goto out;