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(i220-108-176-245.s42.a014.ap.plala.or.jp. [220.108.176.245]) by smtp.gmail.com with ESMTPSA id bi7-20020a170902bf0700b001a9b29b6759sm1724423plb.183.2023.05.09.08.29.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 May 2023 08:29:59 -0700 (PDT) From: Ryusuke Konishi To: Andrew Morton Cc: linux-nilfs@vger.kernel.org, syzbot , syzkaller-bugs@googlegroups.com, linux-kernel@vger.kernel.org Subject: [PATCH] nilfs2: fix use-after-free bug of nilfs_root in nilfs_evict_inode() Date: Wed, 10 May 2023 00:29:56 +0900 Message-Id: <20230509152956.8313-1-konishi.ryusuke@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <00000000000099e5ac05fb1c3b85@google.com> References: <00000000000099e5ac05fb1c3b85@google.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org During unmount process of nilfs2, nothing holds nilfs_root structure after nilfs2 detaches its writer in nilfs_detach_log_writer(). However, since nilfs_evict_inode() uses nilfs_root for some cleanup operations, it may cause use-after-free read if inodes are left in "garbage_list" and released by nilfs_dispose_list() at the end of nilfs_detach_log_writer(). Fix this issue by modifying nilfs_evict_inode() to only clear inode without additional metadata changes that use nilfs_root if the file system is degraded to read-only or the writer is detached. Signed-off-by: Ryusuke Konishi Reported-by: syzbot+78d4495558999f55d1da@syzkaller.appspotmail.com Closes: https://lkml.kernel.org/r/00000000000099e5ac05fb1c3b85@google.com Tested-by: Ryusuke Konishi Cc: stable@vger.kernel.org --- fs/nilfs2/inode.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c index 1310d2d5feb3..a8ce522ac747 100644 --- a/fs/nilfs2/inode.c +++ b/fs/nilfs2/inode.c @@ -917,6 +917,7 @@ void nilfs_evict_inode(struct inode *inode) struct nilfs_transaction_info ti; struct super_block *sb = inode->i_sb; struct nilfs_inode_info *ii = NILFS_I(inode); + struct the_nilfs *nilfs; int ret; if (inode->i_nlink || !ii->i_root || unlikely(is_bad_inode(inode))) { @@ -929,6 +930,23 @@ void nilfs_evict_inode(struct inode *inode) truncate_inode_pages_final(&inode->i_data); + nilfs = sb->s_fs_info; + if (unlikely(sb_rdonly(sb) || !nilfs->ns_writer)) { + /* + * If this inode is about to be disposed after the file system + * has been degraded to read-only due to file system corruption + * or after the writer has been detached, do not make any + * changes that cause writes, just clear it. + * Do this check after read-locking ns_segctor_sem by + * nilfs_transaction_begin() in order to avoid a race with + * the writer detach operation. + */ + clear_inode(inode); + nilfs_clear_inode(inode); + nilfs_transaction_abort(sb); + return; + } + /* TODO: some of the following operations may fail. */ nilfs_truncate_bmap(ii, 0); nilfs_mark_inode_dirty(inode); -- 2.34.1