From patchwork Mon Jun 24 21:03:05 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ajay Kaher X-Patchwork-Id: 11013045 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id CDA321580 for ; Mon, 24 Jun 2019 13:03:17 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C06BB28779 for ; Mon, 24 Jun 2019 13:03:17 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B3EBD28852; Mon, 24 Jun 2019 13:03:17 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.0 required=2.0 tests=BAYES_00,DATE_IN_FUTURE_06_12, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id F0500288E1 for ; Mon, 24 Jun 2019 13:03:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730541AbfFXNDL (ORCPT ); Mon, 24 Jun 2019 09:03:11 -0400 Received: from ex13-edg-ou-002.vmware.com ([208.91.0.190]:28307 "EHLO EX13-EDG-OU-002.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729130AbfFXNDL (ORCPT ); Mon, 24 Jun 2019 09:03:11 -0400 Received: from sc9-mailhost3.vmware.com (10.113.161.73) by EX13-EDG-OU-002.vmware.com (10.113.208.156) with Microsoft SMTP Server id 15.0.1156.6; Mon, 24 Jun 2019 06:03:08 -0700 Received: from akaher-lnx-dev.eng.vmware.com (unknown [10.110.19.203]) by sc9-mailhost3.vmware.com (Postfix) with ESMTP id 69A894135D; Mon, 24 Jun 2019 06:03:03 -0700 (PDT) From: Ajay Kaher To: , , , , , , CC: , , , , , , , , , , , , , , , , , , , , , Hugh Dickins , Mike Rapoport , Linus Torvalds , Greg Kroah-Hartman Subject: [PATCH v4 3/3] [v4.9.y] coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping Date: Tue, 25 Jun 2019 02:33:05 +0530 Message-ID: <1561410186-3919-3-git-send-email-akaher@vmware.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1561410186-3919-1-git-send-email-akaher@vmware.com> References: <1561410186-3919-1-git-send-email-akaher@vmware.com> MIME-Version: 1.0 Received-SPF: None (EX13-EDG-OU-002.vmware.com: akaher@vmware.com does not designate permitted sender hosts) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Andrea Arcangeli coredump: fix race condition between collapse_huge_page() and core dumping commit 59ea6d06cfa9247b586a695c21f94afa7183af74 upstream. When fixing the race conditions between the coredump and the mmap_sem holders outside the context of the process, we focused on mmget_not_zero()/get_task_mm() callers in 04f5866e41fb70 ("coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping"), but those aren't the only cases where the mmap_sem can be taken outside of the context of the process as Michal Hocko noticed while backporting that commit to older -stable kernels. If mmgrab() is called in the context of the process, but then the mm_count reference is transferred outside the context of the process, that can also be a problem if the mmap_sem has to be taken for writing through that mm_count reference. khugepaged registration calls mmgrab() in the context of the process, but the mmap_sem for writing is taken later in the context of the khugepaged kernel thread. collapse_huge_page() after taking the mmap_sem for writing doesn't modify any vma, so it's not obvious that it could cause a problem to the coredump, but it happens to modify the pmd in a way that breaks an invariant that pmd_trans_huge_lock() relies upon. collapse_huge_page() needs the mmap_sem for writing just to block concurrent page faults that call pmd_trans_huge_lock(). Specifically the invariant that "!pmd_trans_huge()" cannot become a "pmd_trans_huge()" doesn't hold while collapse_huge_page() runs. The coredump will call __get_user_pages() without mmap_sem for reading, which eventually can invoke a lockless page fault which will need a functional pmd_trans_huge_lock(). So collapse_huge_page() needs to use mmget_still_valid() to check it's not running concurrently with the coredump... as long as the coredump can invoke page faults without holding the mmap_sem for reading. This has "Fixes: khugepaged" to facilitate backporting, but in my view it's more a bug in the coredump code that will eventually have to be rewritten to stop invoking page faults without the mmap_sem for reading. So the long term plan is still to drop all mmget_still_valid(). Link: http://lkml.kernel.org/r/20190607161558.32104-1-aarcange@redhat.com Fixes: ba76149f47d8 ("thp: khugepaged") Signed-off-by: Andrea Arcangeli Reported-by: Michal Hocko Acked-by: Michal Hocko Acked-by: Kirill A. Shutemov Cc: Oleg Nesterov Cc: Jann Horn Cc: Hugh Dickins Cc: Mike Rapoport Cc: Mike Kravetz Cc: Peter Xu Cc: Jason Gunthorpe Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman [Ajay: Just adjusted to apply on v4.9] Signed-off-by: Ajay Kaher --- include/linux/mm.h | 4 ++++ mm/khugepaged.c | 3 +++ 2 files changed, 7 insertions(+) diff --git a/include/linux/mm.h b/include/linux/mm.h index c239984..8852158 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1194,6 +1194,10 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma, * followed by taking the mmap_sem for writing before modifying the * vmas or anything the coredump pretends not to change from under it. * + * It also has to be called when mmgrab() is used in the context of + * the process, but then the mm_count refcount is transferred outside + * the context of the process to run down_write() on that pinned mm. + * * NOTE: find_extend_vma() called from GUP context is the only place * that can modify the "mm" (notably the vm_start/end) under mmap_sem * for reading and outside the context of the process, so it is also diff --git a/mm/khugepaged.c b/mm/khugepaged.c index e0cfc3a..8217ee5 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1004,6 +1004,9 @@ static void collapse_huge_page(struct mm_struct *mm, * handled by the anon_vma lock + PG_lock. */ down_write(&mm->mmap_sem); + result = SCAN_ANY_PROCESS; + if (!mmget_still_valid(mm)) + goto out; result = hugepage_vma_revalidate(mm, address, &vma); if (result) goto out;