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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9E11EC4332F for ; Tue, 5 Apr 2022 13:48:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1391002AbiDENqf (ORCPT ); Tue, 5 Apr 2022 09:46:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44156 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1347339AbiDEJ0B (ORCPT ); Tue, 5 Apr 2022 05:26:01 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 707E2DE92D; Tue, 5 Apr 2022 02:15:22 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 7B72EB81B75; Tue, 5 Apr 2022 09:15:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CCCF6C385A0; Tue, 5 Apr 2022 09:15:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1649150119; bh=a6oPxCJzwFg+auaLybS3Cz5xCfoOmB6qPAWpGmmbt78=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=SvMPhZaRdqwzMm7sQTiiU53rPmf6/jFTSm5IWaUHQM1601SGqxAcpNS0xcczTdauh s4qRps5G30Krs9YD3Dwl7hxZzkroZ0EncoML4wm8y85AuDS66bNBcSgI0clvoL/5fG ie6IAaGCOaKDihgKGIOkxH36SfUrEJXKErlbFYQo= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot+0d2b0bf32ca5cfd09f2e@syzkaller.appspotmail.com, "Matthew Wilcox (Oracle)" Subject: [PATCH 5.16 0922/1017] XArray: Fix xas_create_range() when multi-order entry present Date: Tue, 5 Apr 2022 09:30:35 +0200 Message-Id: <20220405070421.586364516@linuxfoundation.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220405070354.155796697@linuxfoundation.org> References: <20220405070354.155796697@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Matthew Wilcox (Oracle) commit 3e3c658055c002900982513e289398a1aad4a488 upstream. If there is already an entry present that is of order >= XA_CHUNK_SHIFT when we call xas_create_range(), xas_create_range() will misinterpret that entry as a node and dereference xa_node->parent, generally leading to a crash that looks something like this: general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] CPU: 0 PID: 32 Comm: khugepaged Not tainted 5.17.0-rc8-syzkaller-00003-g56e337f2cf13 #0 RIP: 0010:xa_parent_locked include/linux/xarray.h:1207 [inline] RIP: 0010:xas_create_range+0x2d9/0x6e0 lib/xarray.c:725 It's deterministically reproducable once you know what the problem is, but producing it in a live kernel requires khugepaged to hit a race. While the problem has been present since xas_create_range() was introduced, I'm not aware of a way to hit it before the page cache was converted to use multi-index entries. Fixes: 6b24ca4a1a8d ("mm: Use multi-index entries in the page cache") Reported-by: syzbot+0d2b0bf32ca5cfd09f2e@syzkaller.appspotmail.com Signed-off-by: Matthew Wilcox (Oracle) Signed-off-by: Greg Kroah-Hartman --- lib/test_xarray.c | 22 ++++++++++++++++++++++ lib/xarray.c | 2 ++ 2 files changed, 24 insertions(+) --- a/lib/test_xarray.c +++ b/lib/test_xarray.c @@ -1463,6 +1463,25 @@ unlock: XA_BUG_ON(xa, !xa_empty(xa)); } +static noinline void check_create_range_5(struct xarray *xa, + unsigned long index, unsigned int order) +{ + XA_STATE_ORDER(xas, xa, index, order); + unsigned int i; + + xa_store_order(xa, index, order, xa_mk_index(index), GFP_KERNEL); + + for (i = 0; i < order + 10; i++) { + do { + xas_lock(&xas); + xas_create_range(&xas); + xas_unlock(&xas); + } while (xas_nomem(&xas, GFP_KERNEL)); + } + + xa_destroy(xa); +} + static noinline void check_create_range(struct xarray *xa) { unsigned int order; @@ -1490,6 +1509,9 @@ static noinline void check_create_range( check_create_range_4(xa, (3U << order) + 1, order); check_create_range_4(xa, (3U << order) - 1, order); check_create_range_4(xa, (1U << 24) + 1, order); + + check_create_range_5(xa, 0, order); + check_create_range_5(xa, (1U << order), order); } check_create_range_3(); --- a/lib/xarray.c +++ b/lib/xarray.c @@ -722,6 +722,8 @@ void xas_create_range(struct xa_state *x for (;;) { struct xa_node *node = xas->xa_node; + if (node->shift >= shift) + break; xas->xa_node = xa_parent_locked(xas->xa, node); xas->xa_offset = node->offset - 1; if (node->offset != 0)