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=-9.8 required=3.0 tests=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_GIT autolearn=ham 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 B8EBBC352B6 for ; Tue, 14 Apr 2020 07:56:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 949562074D for ; Tue, 14 Apr 2020 07:56:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=bytedance-com.20150623.gappssmtp.com header.i=@bytedance-com.20150623.gappssmtp.com header.b="c2dnPZDN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2406935AbgDNH44 (ORCPT ); Tue, 14 Apr 2020 03:56:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33980 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S2406749AbgDNH4w (ORCPT ); Tue, 14 Apr 2020 03:56:52 -0400 Received: from mail-pj1-x1042.google.com (mail-pj1-x1042.google.com [IPv6:2607:f8b0:4864:20::1042]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 59217C0A3BDC for ; Tue, 14 Apr 2020 00:56:52 -0700 (PDT) Received: by mail-pj1-x1042.google.com with SMTP id nu11so4883726pjb.1 for ; Tue, 14 Apr 2020 00:56:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=I3PJsIbLnGG+0LNZvpyyPpJKrgmiHJsFy1tLFZ5G7hg=; b=c2dnPZDNCBzzLF/SNgoQWxW/orovCCc+Q/60foy/H9tCof4ofS6NSGK24IxzzfHMq8 vLEVxD1O+wF9gfufRz9gW/l7P0zwkZDzAjvjjLtAecSy+8V6C1dmTz7e/Ztf+yiXfysA jbc3C9WOKMF65vZE4IUUx4f0VMSye4Su9wFOHt3NtmEBLhHhl768i8rZMsbM4Rd9vZEU BhbmS/FmUemOC0oO5F4WTejs0OUXbEmyc4trzUikxxcFvnzN1TNZ9Bp3PFkKE6uhZwy8 9nDP/wZ13X4Ve/arW/Puhsm/4jeSsLHX1+iXSGeQOjlmZHDQFH64cEDx8SG3/3igwwVP q9WA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=I3PJsIbLnGG+0LNZvpyyPpJKrgmiHJsFy1tLFZ5G7hg=; b=JXL6Fr0UTQ9RhLpMdFbZ38wyS+BJ5tcPGRODjdiy0O+dD4CKmsuKM4Ayc0KuSC3FKN qZEtrT6C9Xjazc6PJqcvicr8bCY9fIlFaedjOzh3JlhxDdznN8fIbgPY1iFpEaTu11aU 8+5QE93fd0pwVLbaJeXnrgs/iXezNeC3WJ1tNP3p1+NG0VajMV79/nRWqkXNrHQl1WkF wRfb/JUk7Iut2kBejBPqNB6W24uHcm7wZVkT6MylUgOCyc9lIX5HhJPbJYlt9+IGQ+iA DmaDPeuXJu90tsDCr/5tYLFdihE93lpyWc3YYOZ+pGQn4gq9PxeXKuX0CuHgJ1pseLwi 9EVg== X-Gm-Message-State: AGi0PuZO2R4THJVUXzmih+YmAsPifXKGbd4El/WD8lWev9z6kZBDnIaK 0iPnjQyQd8QKF2oVy3+V82dWQA== X-Google-Smtp-Source: APiQypKpKG9coUBFC0Wb+ShFX1kW+n7CuUoWRS/IMPrXMqWW92Hl10XH9jEO4rfStFoJfPYhH6HyLg== X-Received: by 2002:a17:90a:bf8c:: with SMTP id d12mr26893363pjs.11.1586851011729; Tue, 14 Apr 2020 00:56:51 -0700 (PDT) Received: from Smcdef-MBP.local.net ([103.136.220.69]) by smtp.gmail.com with ESMTPSA id c201sm10568346pfc.73.2020.04.14.00.56.48 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Tue, 14 Apr 2020 00:56:51 -0700 (PDT) From: Muchun Song To: akpm@linux-foundation.org, Markus.Elfring@web.de Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Muchun Song , Xiongchun Duan Subject: [PATCH v2] mm/ksm: Fix NULL pointer dereference when KSM zero page is enabled Date: Tue, 14 Apr 2020 15:56:22 +0800 Message-Id: <20200414075622.69822-1-songmuchun@bytedance.com> X-Mailer: git-send-email 2.21.0 (Apple Git-122) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The find_mergeable_vma can return NULL. In this case, it leads to crash when we access vma->vm_mm(its offset is 0x40) later in write_protect_page. And this case did happen on our server. The following calltrace is captured in kernel 4.19 with KSM zero page enabled. So add a vma check to fix it. -------------------------------------------------------------------------- BUG: unable to handle kernel NULL pointer dereference at 0000000000000040 PGD 0 P4D 0 Oops: 0000 [#1] SMP NOPTI CPU: 9 PID: 510 Comm: ksmd Kdump: loaded Tainted: G OE 4.19.36.bsk.9-amd64 #4.19.36.bsk.9 Hardware name: FOXCONN R-5111/GROOT, BIOS IC1B111F 08/17/2019 RIP: 0010:try_to_merge_one_page+0xc7/0x760 Code: 24 58 65 48 33 34 25 28 00 00 00 89 e8 0f 85 a3 06 00 00 48 83 c4 60 5b 5d 41 5c 41 5d 41 5e 41 5f c3 48 8b 46 08 a8 01 75 b8 <49> 8b 44 24 40 4c 8d 7c 24 20 b9 07 00 00 00 4c 89 e6 4c 89 ff 48 RSP: 0018:ffffadbdd9fffdb0 EFLAGS: 00010246 RAX: ffffda83ffd4be08 RBX: ffffda83ffd4be40 RCX: 0000002c6e800000 RDX: 0000000000000000 RSI: ffffda83ffd4be40 RDI: 0000000000000000 RBP: ffffa11939f02ec0 R08: 0000000094e1a447 R09: 00000000abe76577 R10: 0000000000000962 R11: 0000000000004e6a R12: 0000000000000000 R13: ffffda83b1e06380 R14: ffffa18f31f072c0 R15: ffffda83ffd4be40 FS: 0000000000000000(0000) GS:ffffa0da43b80000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000040 CR3: 0000002c77c0a003 CR4: 00000000007626e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: ? follow_page_pte+0x36d/0x5e0 ksm_scan_thread+0x115e/0x1960 ? remove_wait_queue+0x60/0x60 kthread+0xf5/0x130 ? try_to_merge_with_ksm_page+0x90/0x90 ? kthread_create_worker_on_cpu+0x70/0x70 ret_from_fork+0x1f/0x30 -------------------------------------------------------------------------- Fixes: e86c59b1b12d ("mm/ksm: improve deduplication of zero pages with colouring") Signed-off-by: Muchun Song Signed-off-by: Xiongchun Duan --- Change in v2: Update commit message and patch subject. mm/ksm.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/mm/ksm.c b/mm/ksm.c index a558da9e71770..69b2f85e22d5b 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -2112,8 +2112,11 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) down_read(&mm->mmap_sem); vma = find_mergeable_vma(mm, rmap_item->address); - err = try_to_merge_one_page(vma, page, - ZERO_PAGE(rmap_item->address)); + if (vma) + err = try_to_merge_one_page(vma, page, + ZERO_PAGE(rmap_item->address)); + else + err = -EFAULT; up_read(&mm->mmap_sem); /* * In case of failure, the page was not really empty, so we -- 2.11.0