Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1755626AbcJLQbl (ORCPT <rfc822;w@1wt.eu>);
        Wed, 12 Oct 2016 12:31:41 -0400
Received: from mx3-phx2.redhat.com ([209.132.183.24]:40070 "EHLO
        mx3-phx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1753583AbcJLQbe (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 12 Oct 2016 12:31:34 -0400
Date: Wed, 12 Oct 2016 11:54:17 -0400 (EDT)
From: CAI Qian <caiqian@redhat.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>
Message-ID: <2086376822.528054.1476287657078.JavaMail.zimbra@redhat.com>
In-Reply-To: <1476266223-14325-1-git-send-email-catalin.marinas@arm.com>
References: <1476266223-14325-1-git-send-email-catalin.marinas@arm.com>
Subject: Re: [PATCH] mm: kmemleak: Ensure that the task stack is not freed
 during scanning
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
X-Originating-IP: [10.10.54.9]
X-Mailer: Zimbra 8.0.6_GA_5922 (ZimbraWebClient - SAF10 (Mac)/8.0.6_GA_5922)
Thread-Topic: kmemleak: Ensure that the task stack is not freed during scanning
Thread-Index: gHOiP+eYrzcG8xh1pQWeKeLqD6mAHg==
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 2437
Lines: 68



----- Original Message -----
> From: "Catalin Marinas" <catalin.marinas@arm.com>
> To: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org, "Andrew Morton" <akpm@linux-foundation.org>, "Andy Lutomirski" <luto@kernel.org>,
> "CAI Qian" <caiqian@redhat.com>
> Sent: Wednesday, October 12, 2016 5:57:03 AM
> Subject: [PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning
> 
> Commit 68f24b08ee89 ("sched/core: Free the stack early if
> CONFIG_THREAD_INFO_IN_TASK") may cause the task->stack to be freed
> during kmemleak_scan() execution, leading to either a NULL pointer
> fault (if task->stack is NULL) or kmemleak accessing already freed
> memory. This patch uses the new try_get_task_stack() API to ensure that
> the task stack is not freed during kmemleak stack scanning.
> 
> Fixes: 68f24b08ee89 ("sched/core: Free the stack early if
> CONFIG_THREAD_INFO_IN_TASK")
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: CAI Qian <caiqian@redhat.com>
> Reported-by: CAI Qian <caiqian@redhat.com>
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Tested-by: CAI Qian <caiqian@redhat.com>

> ---
> 
> This was reported in a subsequent comment here:
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=173901
> 
> However, the original bugzilla entry doesn't look related to task stack
> freeing as it was first reported on 4.8-rc8. Andy, sorry for cc'ing you
> to bugzilla, please feel free to remove your email from the bug above (I
> can't seem to be able to do it).
> 
>  mm/kmemleak.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index a5e453cf05c4..e5355a5b423f 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -1453,8 +1453,11 @@ static void kmemleak_scan(void)
>  
>  		read_lock(&tasklist_lock);
>  		do_each_thread(g, p) {
> -			scan_block(task_stack_page(p), task_stack_page(p) +
> -				   THREAD_SIZE, NULL);
> +			void *stack = try_get_task_stack(p);
> +			if (stack) {
> +				scan_block(stack, stack + THREAD_SIZE, NULL);
> +				put_task_stack(p);
> +			}
>  		} while_each_thread(g, p);
>  		read_unlock(&tasklist_lock);
>  	}
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
> 
> 
>