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=-17.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,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 30278C433E9 for ; Tue, 26 Jan 2021 09:03:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F00BC230FE for ; Tue, 26 Jan 2021 09:03:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390764AbhAZJDx (ORCPT ); Tue, 26 Jan 2021 04:03:53 -0500 Received: from mx2.suse.de ([195.135.220.15]:43818 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390779AbhAZJD3 (ORCPT ); Tue, 26 Jan 2021 04:03:29 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1611651761; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=NsFq767DqicIMWlEoRO8qS5sRG2PXynXtaLFhjmIEu4=; b=pXCeu/qY9Thk2TpbX9OBgHX7yOO6B+LqzOa/F98n4jBDXcTEakop0P7Ii1VUxst+eWc8vH wJ7CnhgvomD/LBMjTg/Kx23cGzPN+pH2V3e7xbuFSASPRRCuBfI+QCqV8n1sAd4HtBsWbf g5f91bdTOwFYLCwA73diJ/TDFwBgC1w= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id C746EAC4F; Tue, 26 Jan 2021 09:02:41 +0000 (UTC) Subject: Re: [PATCH] btrfs: avoid double put of block group when emptying cluster To: Josef Bacik , linux-btrfs@vger.kernel.org, kernel-team@fb.com Cc: stable@vger.kernel.org References: <5ca694ff4f8cff4c0ef6896593a1f1d01fbe956d.1611610947.git.josef@toxicpanda.com> From: Nikolay Borisov Autocrypt: addr=nborisov@suse.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <5ca694ff4f8cff4c0ef6896593a1f1d01fbe956d.1611610947.git.josef@toxicpanda.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 25.01.21 г. 23:42 ч., Josef Bacik wrote: > In __btrfs_return_cluster_to_free_space we will bail doing the cleanup > of the cluster if the block group we passed in doesn't match the block > group on the cluster. However we drop a reference to block_group, as > the cluster holds a reference to the block group while it's attached to > the cluster. If cluster->block_group != block_group however then this > is an extra put, which means we'll go negative and free this block group > down the line, leading to a UAF. Was this found by code inspection or did you hit in production. Also why in btrfs_remove_free_space_cache just before __btrfs_return_cluster_to_free_space there is: WARN_ON(cluster->block_group != block_group); IMO this patch should also remove the WARN_ON if it's a valid condition to have the passed bg be different than the one in the cluster. Also that WARN_ON is likely racy since it's done outside of cluster->lock. > > Fix this by simply bailing if the block group we passed in does not > match the block group on the cluster. > > CC: stable@vger.kernel.org > Fixes: fa9c0d795f7b ("Btrfs: rework allocation clustering") > Signed-off-by: Josef Bacik > --- > fs/btrfs/free-space-cache.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c > index 0d6dcb5ff963..8be36cc6cbd8 100644 > --- a/fs/btrfs/free-space-cache.c > +++ b/fs/btrfs/free-space-cache.c > @@ -2711,8 +2711,10 @@ static void __btrfs_return_cluster_to_free_space( > struct rb_node *node; > > spin_lock(&cluster->lock); > - if (cluster->block_group != block_group) > - goto out; > + if (cluster->block_group != block_group) { > + spin_unlock(&cluster->lock); > + return; > + } > > cluster->block_group = NULL; > cluster->window_start = 0; > @@ -2750,8 +2752,6 @@ static void __btrfs_return_cluster_to_free_space( > entry->offset, &entry->offset_index, bitmap); > } > cluster->root = RB_ROOT; > - > -out: > spin_unlock(&cluster->lock); > btrfs_put_block_group(block_group); > } >