From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C019BC433FF for ; Fri, 2 Aug 2019 07:51:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9806C2086A for ; Fri, 2 Aug 2019 07:51:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564732289; bh=kzEEtbjjrdPAyzxrRRGRUcKmUt5I/OGfmVyN7CZTUMo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=COZs+GB13k12U88TsgHvoziCXjpBbd8tpJP73iJVFHdp2N1arYjsKKhMxfDq7K59N lGz3dcwZ/SXB2CdnK3Y4SSNOvufp54HdDYqs4yejX7Abn9KTQ3Ft0C9Fy6r4Hy4hUA lCSVgfsCSYKSdmyRECfqQqjFsbaURKaUtg9fHstc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389415AbfHBHv3 (ORCPT ); Fri, 2 Aug 2019 03:51:29 -0400 Received: from mail.kernel.org ([198.145.29.99]:47576 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729283AbfHBHv2 (ORCPT ); Fri, 2 Aug 2019 03:51:28 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AAAA220644; Fri, 2 Aug 2019 07:51:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564732287; bh=kzEEtbjjrdPAyzxrRRGRUcKmUt5I/OGfmVyN7CZTUMo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KBK3hTK/g/w1aS9eKJB4kyQ5nqJ6ZCuZXyoR+ReQBa1K4Bu7vGSDPSACtOCtfACHo a1B7nFMVv3skMPHQKGVGcFCv4Rbo6B9rHuqN756eyGLeuLaLvYRgs0qCHfIJBDNutS RXDR6sYF4uSLMhhhCLYAW7jWbFfdigVvBzm6JRxw= Date: Fri, 2 Aug 2019 09:51:24 +0200 From: Greg KH To: Ajay Kaher Cc: aarcange@redhat.com, jannh@google.com, oleg@redhat.com, peterx@redhat.com, rppt@linux.ibm.com, jgg@mellanox.com, mhocko@suse.com, jglisse@redhat.com, akpm@linux-foundation.org, mike.kravetz@oracle.com, viro@zeniv.linux.org.uk, riandrews@android.com, arve@android.com, yishaih@mellanox.com, dledford@redhat.com, sean.hefty@intel.com, hal.rosenstock@gmail.com, matanb@mellanox.com, leonro@mellanox.com, torvalds@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, devel@driverdev.osuosl.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, srivatsab@vmware.com, amakhalov@vmware.com Subject: Re: [PATCH v5 1/3] [v4.9.y] coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping Message-ID: <20190802075124.GG26174@kroah.com> References: <1562005928-1929-1-git-send-email-akaher@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1562005928-1929-1-git-send-email-akaher@vmware.com> User-Agent: Mutt/1.12.1 (2019-06-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 02, 2019 at 12:02:05AM +0530, Ajay Kaher wrote: > From: Andrea Arcangeli > > commit 04f5866e41fb70690e28397487d8bd8eea7d712a upstream. > > The core dumping code has always run without holding the mmap_sem for > writing, despite that is the only way to ensure that the entire vma > layout will not change from under it. Only using some signal > serialization on the processes belonging to the mm is not nearly enough. > This was pointed out earlier. For example in Hugh's post from Jul 2017: > > https://lkml.kernel.org/r/alpine.LSU.2.11.1707191716030.2055@eggly.anvils > > "Not strictly relevant here, but a related note: I was very surprised > to discover, only quite recently, how handle_mm_fault() may be called > without down_read(mmap_sem) - when core dumping. That seems a > misguided optimization to me, which would also be nice to correct" > > In particular because the growsdown and growsup can move the > vm_start/vm_end the various loops the core dump does around the vma will > not be consistent if page faults can happen concurrently. > > Pretty much all users calling mmget_not_zero()/get_task_mm() and then > taking the mmap_sem had the potential to introduce unexpected side > effects in the core dumping code. > > Adding mmap_sem for writing around the ->core_dump invocation is a > viable long term fix, but it requires removing all copy user and page > faults and to replace them with get_dump_page() for all binary formats > which is not suitable as a short term fix. > > For the time being this solution manually covers the places that can > confuse the core dump either by altering the vma layout or the vma flags > while it runs. Once ->core_dump runs under mmap_sem for writing the > function mmget_still_valid() can be dropped. > > Allowing mmap_sem protected sections to run in parallel with the > coredump provides some minor parallelism advantage to the swapoff code > (which seems to be safe enough by never mangling any vma field and can > keep doing swapins in parallel to the core dumping) and to some other > corner case. > > In order to facilitate the backporting I added "Fixes: 86039bd3b4e6" > however the side effect of this same race condition in /proc/pid/mem > should be reproducible since before 2.6.12-rc2 so I couldn't add any > other "Fixes:" because there's no hash beyond the git genesis commit. > > Because find_extend_vma() is the only location outside of the process > context that could modify the "mm" structures under mmap_sem for > reading, by adding the mmget_still_valid() check to it, all other cases > that take the mmap_sem for reading don't need the new check after > mmget_not_zero()/get_task_mm(). The expand_stack() in page fault > context also doesn't need the new check, because all tasks under core > dumping are frozen. > > Link: http://lkml.kernel.org/r/20190325224949.11068-1-aarcange@redhat.com > Fixes: 86039bd3b4e6 ("userfaultfd: add new syscall to provide memory externalization") > Signed-off-by: Andrea Arcangeli > Reported-by: Jann Horn > Suggested-by: Oleg Nesterov > Acked-by: Peter Xu > Reviewed-by: Mike Rapoport > Reviewed-by: Oleg Nesterov > Reviewed-by: Jann Horn > Acked-by: Jason Gunthorpe > Acked-by: Michal Hocko > Cc: > Signed-off-by: Andrew Morton > Signed-off-by: Linus Torvalds > Signed-off-by: Greg Kroah-Hartman > [akaher@vmware.com: stable 4.9 backport > - handle binder_update_page_range - mhocko@suse.com] > Signed-off-by: Ajay Kaher > --- > drivers/android/binder.c | 6 ++++++ > fs/proc/task_mmu.c | 18 ++++++++++++++++++ > fs/userfaultfd.c | 9 +++++++++ > include/linux/mm.h | 21 +++++++++++++++++++++ > mm/mmap.c | 6 +++++- > 5 files changed, 59 insertions(+), 1 deletion(-) > > diff --git a/drivers/android/binder.c b/drivers/android/binder.c > index 80499f4..f05ab8f 100644 > --- a/drivers/android/binder.c > +++ b/drivers/android/binder.c > @@ -581,6 +581,12 @@ static int binder_update_page_range(struct binder_proc *proc, int allocate, > if (mm) { > down_write(&mm->mmap_sem); > + if (!mmget_still_valid(mm)) { > + if (allocate == 0) > + goto free_range; > + goto err_no_vma; > + } > + > vma = proc->vma; > if (vma && mm != proc->vma_vm_mm) { > pr_err("%d: vma mm and task mm mismatch\n", > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 5138e78..4b207b1 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -1057,6 +1057,24 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf, This patch is oddly corrupted, and I can't figure out how to fix it up. When applying it, I get following error: patching file drivers/android/binder.c patch: **** malformed patch at line 102: diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c So something is odd here. Can you please fix this up, and resend the series so that they can be applied? thanks, greg k-h