From patchwork Tue Apr 26 08:20:52 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 566524 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 AF9ECC4332F for ; Tue, 26 Apr 2022 09:04:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346220AbiDZJHV (ORCPT ); Tue, 26 Apr 2022 05:07:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51282 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1347645AbiDZJGA (ORCPT ); Tue, 26 Apr 2022 05:06:00 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A9FBB15B95B; Tue, 26 Apr 2022 01:45:13 -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 dfw.source.kernel.org (Postfix) with ESMTPS id 39B1B61344; Tue, 26 Apr 2022 08:45:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2D7FBC385A4; Tue, 26 Apr 2022 08:45:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1650962712; bh=Ppg4K5rXXT1fBHaPj0LOmFveIGcPWCF4xXq+qRCLGQU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=RmySi+RxRHvUQEvwvBf2jFVyMc5imgwSf0U4P6/ALJOKtPr/DI26E8HrFmytO1W4s GRrK0Gl4/60lJ5lYg2aMKPuoE9yh8Td/8Ap6FGFTxrc0HkQEfu/NpbkymyYVgctG1r 1sSjS7+5huGlyFIu1RLHj/GGx0WCR6CFYpNZd/l4= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot+cf4cf13056f85dec2c40@syzkaller.appspotmail.com, "Matthew Wilcox (Oracle)" , Sasha Levin Subject: [PATCH 5.17 057/146] XArray: Disallow sibling entries of nodes Date: Tue, 26 Apr 2022 10:20:52 +0200 Message-Id: <20220426081751.671208688@linuxfoundation.org> X-Mailer: git-send-email 2.36.0 In-Reply-To: <20220426081750.051179617@linuxfoundation.org> References: <20220426081750.051179617@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Matthew Wilcox (Oracle) [ Upstream commit 63b1898fffcd8bd81905b95104ecc52b45a97e21 ] There is a race between xas_split() and xas_load() which can result in the wrong page being returned, and thus data corruption. Fortunately, it's hard to hit (syzbot took three months to find it) and often guarded with VM_BUG_ON(). The anatomy of this race is: thread A thread B order-9 page is stored at index 0x200 lookup of page at index 0x274 page split starts load of sibling entry at offset 9 stores nodes at offsets 8-15 load of entry at offset 8 The entry at offset 8 turns out to be a node, and so we descend into it, and load the page at index 0x234 instead of 0x274. This is hard to fix on the split side; we could replace the entire node that contains the order-9 page instead of replacing the eight entries. Fixing it on the lookup side is easier; just disallow sibling entries that point to nodes. This cannot ever be a useful thing as the descent would not know the correct offset to use within the new node. The test suite continues to pass, but I have not added a new test for this bug. Reported-by: syzbot+cf4cf13056f85dec2c40@syzkaller.appspotmail.com Tested-by: syzbot+cf4cf13056f85dec2c40@syzkaller.appspotmail.com Fixes: 6b24ca4a1a8d ("mm: Use multi-index entries in the page cache") Signed-off-by: Matthew Wilcox (Oracle) Signed-off-by: Sasha Levin --- lib/xarray.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/lib/xarray.c b/lib/xarray.c index 88ca87435e3d..32e1669d5b64 100644 --- a/lib/xarray.c +++ b/lib/xarray.c @@ -207,6 +207,8 @@ static void *xas_descend(struct xa_state *xas, struct xa_node *node) if (xa_is_sibling(entry)) { offset = xa_to_sibling(entry); entry = xa_entry(xas->xa, node, offset); + if (node->shift && xa_is_node(entry)) + entry = XA_RETRY_ENTRY; } xas->xa_offset = offset;