From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt1-f200.google.com (mail-qt1-f200.google.com [209.85.160.200]) by kanga.kvack.org (Postfix) with ESMTP id 655BF8E0001 for ; Mon, 17 Dec 2018 23:38:39 -0500 (EST) Received: by mail-qt1-f200.google.com with SMTP id 42so19646879qtr.7 for ; Mon, 17 Dec 2018 20:38:39 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id h14si4570340qvc.2.2018.12.17.20.38.38 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 17 Dec 2018 20:38:38 -0800 (PST) Date: Mon, 17 Dec 2018 23:38:35 -0500 From: "Michael S. Tsirkin" Subject: Re: [PATCH] Export mm_update_next_owner function for unuse_mm. Message-ID: <20181217233821-mutt-send-email-mst@kernel.org> References: <1545104531-30658-1-git-send-email-gchen.guomin@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1545104531-30658-1-git-send-email-gchen.guomin@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: gchen.guomin@gmail.com Cc: Jason Wang , Christoph Hellwig , Andrew Morton , "Luis R. Rodriguez" , guominchen@tencent.com, "Eric W. Biederman" , Dominik Brodowski , Arnd Bergmann , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Tue, Dec 18, 2018 at 11:42:11AM +0800, gchen.guomin@gmail.com wrote: > From: guomin chen > > When mm->owner is modified by exit_mm, if the new owner directly calls > unuse_mm to exit, it will cause Use-After-Free. Due to the unuse_mm() > directly sets tsk->mm=NULL. > > Under normal circumstances,When do_exit exits, mm->owner will > be updated on exit_mm(). but when the kernel process calls > unuse_mm() and then exits,mm->owner cannot be updated. And it > will point to a task that has been released. > > The current issue flow is as follows: > Process C Process A Process B > qemu-system-x86_64: kernel:vhost_net kernel: vhost_net > open /dev/vhost-net > VHOST_SET_OWNER create kthread vhost-%d create kthread vhost-%d > network init use_mm() use_mm() > ... ... > Abnormal exited > ... > do_exit > exit_mm() > update mm->owner to A > exit_files() > close_files() > kthread_should_stop() unuse_mm() > Stop Process A tsk->mm=NULL > do_exit() > can't update owner > A exit completed vhost-%d rcv first package > vhost-%d build rcv buffer for vq > page fault > access mm & mm->owner > NOW,mm->owner still pointer A > kernel UAF > stop Process B > > Although I am having this issue on vhost_net,But it affects all users of > unuse_mm. > > Cc: "Eric W. Biederman" > Cc: Andrew Morton > Cc: "Luis R. Rodriguez" > Cc: Dominik Brodowski > Cc: Arnd Bergmann > Cc: linux-kernel@vger.kernel.org > Cc: linux-mm@kvack.org > Cc: "Michael S. Tsirkin" > Cc: Jason Wang > Cc: Christoph Hellwig > Signed-off-by: guomin chen > --- > kernel/exit.c | 1 + > mm/mmu_context.c | 1 + > 2 files changed, 2 insertions(+) > > diff --git a/kernel/exit.c b/kernel/exit.c > index 0e21e6d..9e046dd 100644 > --- a/kernel/exit.c > +++ b/kernel/exit.c > @@ -486,6 +486,7 @@ void mm_update_next_owner(struct mm_struct *mm) > task_unlock(c); > put_task_struct(c); > } > +EXPORT_SYMBOL(mm_update_next_owner); > #endif /* CONFIG_MEMCG */ > > /* So why export it? Is that still needed? > diff --git a/mm/mmu_context.c b/mm/mmu_context.c > index 3e612ae..9eb81aa 100644 > --- a/mm/mmu_context.c > +++ b/mm/mmu_context.c > @@ -60,5 +60,6 @@ void unuse_mm(struct mm_struct *mm) > /* active_mm is still 'mm' */ > enter_lazy_tlb(mm, tsk); > task_unlock(tsk); > + mm_update_next_owner(mm); > } > EXPORT_SYMBOL_GPL(unuse_mm); > -- > 1.8.3.1