Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753363AbdFGXlm (ORCPT ); Wed, 7 Jun 2017 19:41:42 -0400 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:50584 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752979AbdFGXE0 (ORCPT ); Wed, 7 Jun 2017 19:04:26 -0400 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux@roeck-us.net Cc: "bsegall@google.com" , Andrew Morton , Linus Torvalds , Willy Tarreau Subject: [PATCH 3.10 200/250] ptrace: fix PTRACE_LISTEN race corrupting task->state Date: Thu, 8 Jun 2017 00:59:46 +0200 Message-Id: <1496876436-32402-201-git-send-email-w@1wt.eu> X-Mailer: git-send-email 2.8.0.rc2.1.gbe9624a In-Reply-To: <1496876436-32402-1-git-send-email-w@1wt.eu> References: <1496876436-32402-1-git-send-email-w@1wt.eu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2234 Lines: 59 From: "bsegall@google.com" commit 5402e97af667e35e54177af8f6575518bf251d51 upstream. In PT_SEIZED + LISTEN mode STOP/CONT 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 TRACED while the task is still on the rq wake_list, corrupting it. Oleg said: "The kernel can crash or this can lead to other hard-to-debug problems. In short, "task->state = TASK_TRACED" in ptrace_unfreeze_traced() assumes that nobody else can wake it up, but PTRACE_LISTEN breaks the contract. Obviusly it is very wrong to manipulate task->state if this task is already running, or WAKING, or it sleeps again" [akpm@linux-foundation.org: coding-style fixes] Fixes: 9899d11f ("ptrace: ensure arch_ptrace/ptrace_request can never race with SIGKILL") Link: http://lkml.kernel.org/r/xm26y3vfhmkp.fsf_-_@bsegall-linux.mtv.corp.google.com Signed-off-by: Ben Segall Acked-by: Oleg Nesterov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Willy Tarreau --- kernel/ptrace.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 72b0b3e..d34c05a 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -150,11 +150,17 @@ static void ptrace_unfreeze_traced(struct task_struct *task) WARN_ON(!task->ptrace || task->parent != current); + /* + * PTRACE_LISTEN can allow ptrace_trap_notify to wake us up remotely. + * Recheck state under the lock to close this race. + */ spin_lock_irq(&task->sighand->siglock); - if (__fatal_signal_pending(task)) - wake_up_state(task, __TASK_TRACED); - else - task->state = TASK_TRACED; + if (task->state == __TASK_TRACED) { + if (__fatal_signal_pending(task)) + wake_up_state(task, __TASK_TRACED); + else + task->state = TASK_TRACED; + } spin_unlock_irq(&task->sighand->siglock); } -- 2.8.0.rc2.1.gbe9624a