From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f199.google.com (mail-qk0-f199.google.com [209.85.220.199]) by kanga.kvack.org (Postfix) with ESMTP id 6DDCB440846 for ; Thu, 24 Aug 2017 09:20:46 -0400 (EDT) Received: by mail-qk0-f199.google.com with SMTP id d190so2691190qkb.6 for ; Thu, 24 Aug 2017 06:20:46 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id w23si3811261qtb.70.2017.08.24.06.20.45 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 24 Aug 2017 06:20:45 -0700 (PDT) Date: Thu, 24 Aug 2017 15:20:41 +0200 From: Oleg Nesterov Subject: Re: [PATCH] fork: fix incorrect fput of ->exe_file causing use-after-free Message-ID: <20170824132041.GA22882@redhat.com> References: <20170823211408.31198-1-ebiggers3@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170823211408.31198-1-ebiggers3@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Eric Biggers Cc: linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org, Dmitry Vyukov , Ingo Molnar , Konstantin Khlebnikov , Michal Hocko , Peter Zijlstra , Vlastimil Babka , stable@vger.kernel.org, Eric Biggers On 08/23, Eric Biggers wrote: > > From: Eric Biggers > > Commit 7c051267931a ("mm, fork: make dup_mmap wait for mmap_sem for > write killable") made it possible to kill a forking task while it is > waiting to acquire its ->mmap_sem for write, in dup_mmap(). However, it > was overlooked that this introduced an new error path before a reference > is taken on the mm_struct's ->exe_file. Hmm. Unless I am totally confused, the same problem with mm->exol_area? I'll recheck.... > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -806,6 +806,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p, > mm_init_cpumask(mm); > mm_init_aio(mm); > mm_init_owner(mm, p); > + RCU_INIT_POINTER(mm->exe_file, NULL); Can't we simply move RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm)); from dup_mmap() here? Afaics this doesn't need mmap_sem. Good catch! Oleg. -- 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: email@kvack.org