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=-19.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT 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 35D40C4161D for ; Mon, 10 May 2021 10:56:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0B89961624 for ; Mon, 10 May 2021 10:56:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234687AbhEJK4v (ORCPT ); Mon, 10 May 2021 06:56:51 -0400 Received: from mail.kernel.org ([198.145.29.99]:57152 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233066AbhEJKpB (ORCPT ); Mon, 10 May 2021 06:45:01 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id A60D761624; Mon, 10 May 2021 10:34:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1620642875; bh=HjluC2N3I32cUFD4y6+oqHofg8Wl0e8qOQOIPhatPTo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=EupUWmZyWX7aO+5ZUkRR97qT37TnZ/XJsU/AnFTFhh9M6z+bAoJCNUc4SHecxuTvP 7Tx5HDvsumwS/KuxIJhjmibMzztbLeQSYjKaDaKAmMpv+wp1X7tIx1PwYM2bcOa6CJ 3cJFe/eN20iJHHfS1aqkGzgq0JOfCDMC0IEcm4ak= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Josef Bacik , Qu Wenruo , David Sterba Subject: [PATCH 5.10 043/299] btrfs: handle remount to no compress during compression Date: Mon, 10 May 2021 12:17:20 +0200 Message-Id: <20210510102006.275929345@linuxfoundation.org> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210510102004.821838356@linuxfoundation.org> References: <20210510102004.821838356@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: Qu Wenruo commit 1d8ba9e7e785b6625f4d8e978e8a284b144a7077 upstream. [BUG] When running btrfs/071 with inode_need_compress() removed from compress_file_range(), we got the following crash: BUG: kernel NULL pointer dereference, address: 0000000000000018 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page Workqueue: btrfs-delalloc btrfs_work_helper [btrfs] RIP: 0010:compress_file_range+0x476/0x7b0 [btrfs] Call Trace: ? submit_compressed_extents+0x450/0x450 [btrfs] async_cow_start+0x16/0x40 [btrfs] btrfs_work_helper+0xf2/0x3e0 [btrfs] process_one_work+0x278/0x5e0 worker_thread+0x55/0x400 ? process_one_work+0x5e0/0x5e0 kthread+0x168/0x190 ? kthread_create_worker_on_cpu+0x70/0x70 ret_from_fork+0x22/0x30 ---[ end trace 65faf4eae941fa7d ]--- This is already after the patch "btrfs: inode: fix NULL pointer dereference if inode doesn't need compression." [CAUSE] @pages is firstly created by kcalloc() in compress_file_extent(): pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS); Then passed to btrfs_compress_pages() to be utilized there: ret = btrfs_compress_pages(... pages, &nr_pages, ...); btrfs_compress_pages() will initialize each page as output, in zlib_compress_pages() we have: pages[nr_pages] = out_page; nr_pages++; Normally this is completely fine, but there is a special case which is in btrfs_compress_pages() itself: switch (type) { default: return -E2BIG; } In this case, we didn't modify @pages nor @out_pages, leaving them untouched, then when we cleanup pages, the we can hit NULL pointer dereference again: if (pages) { for (i = 0; i < nr_pages; i++) { WARN_ON(pages[i]->mapping); put_page(pages[i]); } ... } Since pages[i] are all initialized to zero, and btrfs_compress_pages() doesn't change them at all, accessing pages[i]->mapping would lead to NULL pointer dereference. This is not possible for current kernel, as we check inode_need_compress() before doing pages allocation. But if we're going to remove that inode_need_compress() in compress_file_extent(), then it's going to be a problem. [FIX] When btrfs_compress_pages() hits its default case, modify @out_pages to 0 to prevent such problem from happening. Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=212331 CC: stable@vger.kernel.org # 5.10+ Reviewed-by: Josef Bacik Signed-off-by: Qu Wenruo Reviewed-by: David Sterba Signed-off-by: David Sterba Signed-off-by: Greg Kroah-Hartman --- fs/btrfs/compression.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) --- a/fs/btrfs/compression.c +++ b/fs/btrfs/compression.c @@ -80,10 +80,15 @@ static int compression_compress_pages(in case BTRFS_COMPRESS_NONE: default: /* - * This can't happen, the type is validated several times - * before we get here. As a sane fallback, return what the - * callers will understand as 'no compression happened'. + * This can happen when compression races with remount setting + * it to 'no compress', while caller doesn't call + * inode_need_compress() to check if we really need to + * compress. + * + * Not a big deal, just need to inform caller that we + * haven't allocated any pages yet. */ + *out_pages = 0; return -E2BIG; } }