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=-9.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,USER_AGENT_GIT autolearn=ham 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 995BFC4360F for ; Wed, 20 Feb 2019 06:55:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6AE532183F for ; Wed, 20 Feb 2019 06:55:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550645715; bh=pQGi1F1UQ5iygO0I/HeMTMFMllZgYXcN2XSBk1OeH24=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=mhpMUv34T9GkDH+2Wootn6Luhy6+2WCtpgnM6Uw77MyO3EG2pXcIux8vOvyG36Fli DZ2bmG0Np4mQWZ2lAEMcRxWnlgvjte0FbI047Uqq5eiN8g2qtK+uTBqIkOpdHf3de5 9XaqELLGjM6Cg6Umgl6QNGplIVVHFf4cBMidef9Q= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730543AbfBTGzO (ORCPT ); Wed, 20 Feb 2019 01:55:14 -0500 Received: from mail.kernel.org ([198.145.29.99]:54402 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730654AbfBTGym (ORCPT ); Wed, 20 Feb 2019 01:54:42 -0500 Received: from sol.localdomain (c-107-3-167-184.hsd1.ca.comcast.net [107.3.167.184]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AF89121917; Wed, 20 Feb 2019 06:54:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1550645682; bh=pQGi1F1UQ5iygO0I/HeMTMFMllZgYXcN2XSBk1OeH24=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=PZontyBXZBYfDlmWUy8JIpGmo5IELJ+2TrvYpyZmOq2te5DOeLdTIcpSlTNPbsRAI ceJ9kIN+WQNBBytMXerUHZO/ZS/NdFPoT4+xv/FfOkD9C2Dop9p1Sk8iMZsxq5bUcE IDPgiVI+YkEwneLLMUU9bHFC1XSv5kVrBZ8QqSJU= From: Eric Biggers To: linux-fscrypt@vger.kernel.org Cc: Satya Tangirala , linux-api@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, keyrings@vger.kernel.org, linux-mtd@lists.infradead.org, linux-crypto@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, Paul Crowley Subject: [RFC PATCH v3 14/18] fscrypt: require that key be added when setting a v2 encryption policy Date: Tue, 19 Feb 2019 22:52:45 -0800 Message-Id: <20190220065249.32099-15-ebiggers@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190220065249.32099-1-ebiggers@kernel.org> References: <20190220065249.32099-1-ebiggers@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Eric Biggers By looking up the master keys in a filesystem-level keyring rather than in the calling processes' key hierarchy, it becomes possible for a user to set an encryption policy which refers to some key they don't actually know, then encrypt their files using that key. Cryptographically this isn't much of a problem, but the semantics of this would be a bit weird. Thus, enforce that a v2 encryption policy can only be set if the user has previously added the key, or has capable(CAP_FOWNER). We tolerate that this problem will continue to exist for v1 encryption policies, however; there is no way around that. Signed-off-by: Eric Biggers --- fs/crypto/fscrypt_private.h | 3 +++ fs/crypto/keyring.c | 47 +++++++++++++++++++++++++++++++++++++ fs/crypto/policy.c | 6 +++++ 3 files changed, 56 insertions(+) diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h index b81d4a59056d..881b43cb1d59 100644 --- a/fs/crypto/fscrypt_private.h +++ b/fs/crypto/fscrypt_private.h @@ -409,6 +409,9 @@ extern struct key * fscrypt_find_master_key(struct super_block *sb, const struct fscrypt_key_specifier *mk_spec); +extern int fscrypt_verify_key_added(struct super_block *sb, + const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]); + extern int __init fscrypt_init_keyring(void); extern void fscrypt_exit_keyring(void); diff --git a/fs/crypto/keyring.c b/fs/crypto/keyring.c index 48e7ab8a42e5..dae4423c6657 100644 --- a/fs/crypto/keyring.c +++ b/fs/crypto/keyring.c @@ -556,6 +556,53 @@ int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg) } EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key); +/* + * Verify that the current user has added a master key with the given identifier + * (returns -ENOKEY if not). This is needed to prevent a user from encrypting + * their files using some other user's key which they don't actually know. + * Cryptographically this isn't much of a problem, but the semantics of this + * would be a bit weird, so it's best to just forbid it. + * + * The system administrator (CAP_FOWNER) can override this, which should be + * enough for any use cases where encryption policies are being set using keys + * that were chosen ahead of time but aren't available at the moment. + * + * Note that the key may have already removed by the time this returns, but + * that's okay; we just care whether the key was there at some point. + * + * Return: 0 if the key is added, -ENOKEY if it isn't, or another -errno code + */ +int fscrypt_verify_key_added(struct super_block *sb, + const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]) +{ + struct fscrypt_key_specifier mk_spec; + struct key *key, *mk_user; + struct fscrypt_master_key *mk; + int err; + + mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER; + memcpy(mk_spec.u.identifier, identifier, FSCRYPT_KEY_IDENTIFIER_SIZE); + + key = fscrypt_find_master_key(sb, &mk_spec); + if (IS_ERR(key)) { + err = PTR_ERR(key); + goto out; + } + mk = key->payload.data[0]; + mk_user = find_master_key_user(mk); + if (IS_ERR(mk_user)) { + err = PTR_ERR(mk_user); + } else { + key_put(mk_user); + err = 0; + } + key_put(key); +out: + if (err == -ENOKEY && capable(CAP_FOWNER)) + err = 0; + return err; +} + static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk) { struct fscrypt_info *ci; diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c index 07fec2f7fc72..456c25796844 100644 --- a/fs/crypto/policy.c +++ b/fs/crypto/policy.c @@ -209,6 +209,7 @@ static int set_encryption_policy(struct inode *inode, { union fscrypt_context ctx; int ctxsize; + int err; if (!fscrypt_supported_policy(policy)) return -EINVAL; @@ -227,6 +228,11 @@ static int set_encryption_policy(struct inode *inode, */ pr_warn_once("%s (pid %d) is setting deprecated v1 encryption policy; recommend upgrading to v2.\n", current->comm, current->pid); + } else { + err = fscrypt_verify_key_added(inode->i_sb, + policy->v2.master_key_identifier); + if (err) + return err; } ctxsize = fscrypt_new_context_from_policy(&ctx, policy); -- 2.20.1