From patchwork Mon Dec 28 19:12:08 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Biggers X-Patchwork-Id: 352930 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=-19.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, 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 1B25FC4332E for ; Mon, 28 Dec 2020 19:14:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E023B229EF for ; Mon, 28 Dec 2020 19:13:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729051AbgL1TN6 (ORCPT ); Mon, 28 Dec 2020 14:13:58 -0500 Received: from mail.kernel.org ([198.145.29.99]:41784 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729001AbgL1TN5 (ORCPT ); Mon, 28 Dec 2020 14:13:57 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 8D43022AEC; Mon, 28 Dec 2020 19:13:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1609182796; bh=CSH3X564W0JPlwNl9CEL8TvVblDR1cIHbVAcwArSnWE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=px2NTNVbrivYq0hGtt+5pRW95Kf6LA2VeVdzzT0yLUD/z6qMDjgt7t/yqoCFDtA5C xtpHUHBScrWM5BzOmvbAIjmWUvnddqm2YO17xPBIR8qUzHGOahkiYAa60g5gbIKC2v B2jEVE/VaAHlbBRs62CkYYrbGMmkJOHBb84bvAHovicqy8eW/1aok6YcPZXq1ztE8D 08clrSfTt5XLcPZX51tXQafkaDxZesLtyD7bFBL0wpMMxcivbZlTzvRvaGIV0iAcM+ cOvqIiXCVT1SdHuOghXDeVU0C7+6DGJtR1KebzUBVdTHczWBX8tWx5TUiV+9KXuNLw w0KMlTNxU4N/g== From: Eric Biggers To: stable@vger.kernel.org Cc: linux-fscrypt@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-mtd@lists.infradead.org Subject: [PATCH 4.19 1/4] fscrypt: add fscrypt_is_nokey_name() Date: Mon, 28 Dec 2020 11:12:08 -0800 Message-Id: <20201228191211.138300-2-ebiggers@kernel.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201228191211.138300-1-ebiggers@kernel.org> References: <20201228191211.138300-1-ebiggers@kernel.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Eric Biggers commit 159e1de201b6fca10bfec50405a3b53a561096a8 upstream. It's possible to create a duplicate filename in an encrypted directory by creating a file concurrently with adding the encryption key. Specifically, sys_open(O_CREAT) (or sys_mkdir(), sys_mknod(), or sys_symlink()) can lookup the target filename while the directory's encryption key hasn't been added yet, resulting in a negative no-key dentry. The VFS then calls ->create() (or ->mkdir(), ->mknod(), or ->symlink()) because the dentry is negative. Normally, ->create() would return -ENOKEY due to the directory's key being unavailable. However, if the key was added between the dentry lookup and ->create(), then the filesystem will go ahead and try to create the file. If the target filename happens to already exist as a normal name (not a no-key name), a duplicate filename may be added to the directory. In order to fix this, we need to fix the filesystems to prevent ->create(), ->mkdir(), ->mknod(), and ->symlink() on no-key names. (->rename() and ->link() need it too, but those are already handled correctly by fscrypt_prepare_rename() and fscrypt_prepare_link().) In preparation for this, add a helper function fscrypt_is_nokey_name() that filesystems can use to do this check. Use this helper function for the existing checks that fs/crypto/ does for rename and link. Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20201118075609.120337-2-ebiggers@kernel.org Signed-off-by: Eric Biggers --- fs/crypto/hooks.c | 10 +++++----- include/linux/fscrypt_notsupp.h | 5 +++++ include/linux/fscrypt_supp.h | 29 +++++++++++++++++++++++++++++ 3 files changed, 39 insertions(+), 5 deletions(-) diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c index 042d5b44f4ed9..aa86cb2db8236 100644 --- a/fs/crypto/hooks.c +++ b/fs/crypto/hooks.c @@ -58,8 +58,8 @@ int __fscrypt_prepare_link(struct inode *inode, struct inode *dir, if (err) return err; - /* ... in case we looked up ciphertext name before key was added */ - if (dentry->d_flags & DCACHE_ENCRYPTED_NAME) + /* ... in case we looked up no-key name before key was added */ + if (fscrypt_is_nokey_name(dentry)) return -ENOKEY; if (!fscrypt_has_permitted_context(dir, inode)) @@ -83,9 +83,9 @@ int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry, if (err) return err; - /* ... in case we looked up ciphertext name(s) before key was added */ - if ((old_dentry->d_flags | new_dentry->d_flags) & - DCACHE_ENCRYPTED_NAME) + /* ... in case we looked up no-key name(s) before key was added */ + if (fscrypt_is_nokey_name(old_dentry) || + fscrypt_is_nokey_name(new_dentry)) return -ENOKEY; if (old_dir != new_dir) { diff --git a/include/linux/fscrypt_notsupp.h b/include/linux/fscrypt_notsupp.h index 24b261e49dc14..93304cfeb6016 100644 --- a/include/linux/fscrypt_notsupp.h +++ b/include/linux/fscrypt_notsupp.h @@ -24,6 +24,11 @@ static inline bool fscrypt_dummy_context_enabled(struct inode *inode) return false; } +static inline bool fscrypt_is_nokey_name(const struct dentry *dentry) +{ + return false; +} + /* crypto.c */ static inline void fscrypt_enqueue_decrypt_work(struct work_struct *work) { diff --git a/include/linux/fscrypt_supp.h b/include/linux/fscrypt_supp.h index 8641e20694ce9..0409c14ae1de4 100644 --- a/include/linux/fscrypt_supp.h +++ b/include/linux/fscrypt_supp.h @@ -58,6 +58,35 @@ static inline bool fscrypt_dummy_context_enabled(struct inode *inode) inode->i_sb->s_cop->dummy_context(inode); } +/** + * fscrypt_is_nokey_name() - test whether a dentry is a no-key name + * @dentry: the dentry to check + * + * This returns true if the dentry is a no-key dentry. A no-key dentry is a + * dentry that was created in an encrypted directory that hasn't had its + * encryption key added yet. Such dentries may be either positive or negative. + * + * When a filesystem is asked to create a new filename in an encrypted directory + * and the new filename's dentry is a no-key dentry, it must fail the operation + * with ENOKEY. This includes ->create(), ->mkdir(), ->mknod(), ->symlink(), + * ->rename(), and ->link(). (However, ->rename() and ->link() are already + * handled by fscrypt_prepare_rename() and fscrypt_prepare_link().) + * + * This is necessary because creating a filename requires the directory's + * encryption key, but just checking for the key on the directory inode during + * the final filesystem operation doesn't guarantee that the key was available + * during the preceding dentry lookup. And the key must have already been + * available during the dentry lookup in order for it to have been checked + * whether the filename already exists in the directory and for the new file's + * dentry not to be invalidated due to it incorrectly having the no-key flag. + * + * Return: %true if the dentry is a no-key name + */ +static inline bool fscrypt_is_nokey_name(const struct dentry *dentry) +{ + return dentry->d_flags & DCACHE_ENCRYPTED_NAME; +} + /* crypto.c */ extern void fscrypt_enqueue_decrypt_work(struct work_struct *); extern struct fscrypt_ctx *fscrypt_get_ctx(const struct inode *, gfp_t);