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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 745F2C15505 for ; Thu, 4 Mar 2021 00:11:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5FAC564EDF for ; Thu, 4 Mar 2021 00:11:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354775AbhCDAK6 (ORCPT ); Wed, 3 Mar 2021 19:10:58 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:52257 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1392012AbhCCXAY (ORCPT ); Wed, 3 Mar 2021 18:00:24 -0500 Received: from 1.general.cking.uk.vpn ([10.172.193.212]) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1lHaSm-0004sy-9V; Wed, 03 Mar 2021 22:59:28 +0000 Subject: Re: f2fs_convert_inline_inode causing rebalance based on random uninitialized value in dn.node_changed To: Jaegeuk Kim Cc: Changman Lee , Chao Yu , linux-f2fs-devel@lists.sourceforge.net, "linux-kernel@vger.kernel.org" References: <9fcca081-9a60-8ae3-5cac-d8aa38c38ff2@canonical.com> From: Colin Ian King Message-ID: <9b586bbb-bb94-6fdf-c9a4-9415dbc6d8d0@canonical.com> Date: Wed, 3 Mar 2021 22:59:27 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/03/2021 19:44, Jaegeuk Kim wrote: > On 03/02, Colin Ian King wrote: >> Hi, >> >> Static analysis on linux-next detected a potential uninitialized >> variable dn.node_changed that does not get set when a call to >> f2fs_get_node_page() fails. This uninitialized value gets used in the >> call to f2fs_balance_fs() that may or not may not balances dirty node >> and dentry pages depending on the uninitialized state of the variable. >> >> I believe the issue was introduced by commit: >> >> commit 2a3407607028f7c780f1c20faa4e922bf631d340 >> Author: Jaegeuk Kim >> Date: Tue Dec 22 13:23:35 2015 -0800 >> >> f2fs: call f2fs_balance_fs only when node was changed >> >> >> The analysis is a follows: >> >> 184 int f2fs_convert_inline_inode(struct inode *inode) >> 185 { >> 186 struct f2fs_sb_info *sbi = F2FS_I_SB(inode); >> >> 1. var_decl: Declaring variable dn without initializer. >> >> 187 struct dnode_of_data dn; >> >> NOTE dn is not initialized here. >> >> 188 struct page *ipage, *page; >> 189 int err = 0; >> 190 >> >> 2. Condition !f2fs_has_inline_data(inode), taking false branch. >> 3. Condition f2fs_hw_is_readonly(sbi), taking false branch. >> 4. Condition f2fs_readonly(sbi->sb), taking false branch. >> >> 191 if (!f2fs_has_inline_data(inode) || >> 192 f2fs_hw_is_readonly(sbi) || >> f2fs_readonly(sbi->sb)) >> 193 return 0; >> 194 >> 195 err = dquot_initialize(inode); >> >> 5. Condition err, taking false branch. >> >> 196 if (err) >> 197 return err; >> 198 >> 199 page = f2fs_grab_cache_page(inode->i_mapping, 0, false); >> >> 6. Condition !page, taking false branch. >> >> 200 if (!page) >> 201 return -ENOMEM; >> 202 >> 203 f2fs_lock_op(sbi); >> 204 >> 205 ipage = f2fs_get_node_page(sbi, inode->i_ino); >> >> 7. Condition IS_ERR(ipage), taking true branch. >> >> 206 if (IS_ERR(ipage)) { >> 207 err = PTR_ERR(ipage); >> >> 8. Jumping to label out. >> >> 208 goto out; >> 209 } >> 210 >> >> NOTE: set_new_dnode memset's dn so sets the flag to false, but we >> don't get to this memset if IS_ERR(ipage) above is true. >> >> 211 set_new_dnode(&dn, inode, ipage, ipage, 0); >> 212 >> 213 if (f2fs_has_inline_data(inode)) >> 214 err = f2fs_convert_inline_page(&dn, page); >> 215 >> 216 f2fs_put_dnode(&dn); >> 217 out: >> 218 f2fs_unlock_op(sbi); >> 219 >> 220 f2fs_put_page(page, 1); >> 221 >> >> Uninitialized scalar variable: >> >> 9. uninit_use_in_call: Using uninitialized value dn.node_changed when >> calling f2fs_balance_fs. >> >> 222 f2fs_balance_fs(sbi, dn.node_changed); >> 223 >> 224 return err; >> 225 } >> >> I think a suitable fix will be to set dn.node_changed to false on in >> line 207-208 but I'm concerned if I'm missing something subtle to the >> rebalancing if I do this. >> >> Comments? > > Thank you for the report. Yes, it seems that's a right call and we need to > check the error to decide calling f2fs_balance_fs() in line 222, since > set_new_dnode() is used to set all the fields in dnode_of_data. So, if you > don't mind, could you please post a patch? Just to clarify, just setting dn.node_changes to false is enough? I'm not entirely sure what you meant when you wrote "and we need to check the error to decide calling f2fs_balance_fs() in line 222". Colin > > Thanks, > >> >> Colin >>