From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754521AbdBUSs0 (ORCPT ); Tue, 21 Feb 2017 13:48:26 -0500 Received: from mail-pg0-f47.google.com ([74.125.83.47]:35771 "EHLO mail-pg0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753343AbdBUSr5 (ORCPT ); Tue, 21 Feb 2017 13:47:57 -0500 From: bsegall@google.com To: linux-kernel@vger.kernel.org, Roland McGrath , Oleg Nesterov Subject: [PATCH] ptrace: fix PTRACE_LISTEN race corrupting task->state Date: Tue, 21 Feb 2017 10:47:54 -0800 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In PT_SEIZED + LISTEN mode SIGSTOP/SIGCONT signals cause a wakeup against __TASK_TRACED. If this races with the ptrace_unfreeze_traced at the end of a PTRACE_LISTEN, this can wake the task /after/ the check against __TASK_TRACED, but before the reset of state to TASK_TRACED. This causes it to instead clobber TASK_WAKING, allowing a subsequent wakeup against TASK_TRACED while the task is still on the rq wake_list, corrupting it. Signed-off-by: Ben Segall --- kernel/ptrace.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 0af928712174..852d71440ded 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -184,10 +184,14 @@ static void ptrace_unfreeze_traced(struct task_struct *task) WARN_ON(!task->ptrace || task->parent != current); + /* + * Double check __TASK_TRACED under the lock to prevent corrupting state + * in case of a ptrace_trap_notify wakeup + */ spin_lock_irq(&task->sighand->siglock); if (__fatal_signal_pending(task)) wake_up_state(task, __TASK_TRACED); - else + else if (task->state == __TASK_TRACED) task->state = TASK_TRACED; spin_unlock_irq(&task->sighand->siglock); } -- 2.11.0.483.g087da7b7c-goog