From patchwork Wed Oct 19 16:38:20 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nikolaus Voss X-Patchwork-Id: 13012173 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B8EA0C433FE for ; Wed, 19 Oct 2022 16:45:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229592AbiJSQph (ORCPT ); Wed, 19 Oct 2022 12:45:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40432 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229497AbiJSQpg (ORCPT ); Wed, 19 Oct 2022 12:45:36 -0400 Received: from mail.steuer-voss.de (mail.steuer-voss.de [85.183.69.95]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7AF9DB6D; Wed, 19 Oct 2022 09:45:31 -0700 (PDT) X-Virus-Scanned: Debian amavisd-new at mail.steuer-voss.de Received: by mail.steuer-voss.de (Postfix, from userid 1000) id B70DF1C59; Wed, 19 Oct 2022 18:45:26 +0200 (CEST) From: Nikolaus Voss To: Mimi Zohar , David Howells , Jarkko Sakkinen , James Morris , "Serge E. Hallyn" , Yael Tzur , Cyril Hrubis , Petr Vorel Cc: linux-integrity@vger.kernel.org, keyrings@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Date: Wed, 19 Oct 2022 18:38:20 +0200 Subject: [PATCH v6] KEYS: encrypted: fix key instantiation with user-provided data Message-Id: <20221019164526.B70DF1C59@mail.steuer-voss.de> Precedence: bulk List-ID: Commit cd3bc044af48 ("KEYS: encrypted: Instantiate key with user-provided decrypted data") added key instantiation with user provided decrypted data. The user data is hex-ascii-encoded but was just memcpy'ed to the binary buffer. Fix this to use hex2bin instead. Old keys created from user provided decrypted data saved with "keyctl pipe" are still valid, however if the key is recreated from decrypted data the old key must be converted to the correct format. This can be done with a small shell script, e.g.: BROKENKEY=abcdefABCDEF1234567890aaaaaaaaaa NEWKEY=$(echo -ne $BROKENKEY | xxd -p -c32) keyctl add user masterkey "$(cat masterkey.bin)" @u keyctl add encrypted testkey "new user:masterkey 32 $NEWKEY" @u However, NEWKEY is still broken: If for BROKENKEY 32 bytes were specified, a brute force attacker knowing the key properties would only need to try at most 2^(16*8) keys, as if the key was only 16 bytes long. The security issue is a result of the combination of limiting the input range to hex-ascii and using memcpy() instead of hex2bin(). It could have been fixed either by allowing binary input or using hex2bin() (and doubling the ascii input key length). This patch implements the latter. The corresponding test for the Linux Test Project ltp has also been fixed (see link below). Fixes: cd3bc044af48 ("KEYS: encrypted: Instantiate key with user-provided decrypted data") Cc: stable@kernel.org Link: https://lore.kernel.org/ltp/20221006081709.92303897@mail.steuer-voss.de/ Reviewed-by: Mimi Zohar Signed-off-by: Nikolaus Voss --- Changes ======= v6: - fix checkpatch warnings v5: - explain security issue in commit message, add Reviewd-by v4: - change "Link:" address v3: - use generated random key in example, reformat commit message v2: - clarify commit message, add example to recover old/broken keys - improve example in Documentation/security/keys/trusted-encrypted.rst - add link to ltp patch Documentation/security/keys/trusted-encrypted.rst | 3 ++- security/keys/encrypted-keys/encrypted.c | 6 +++--- 2 files changed, 5 insertions(+), 4 deletions(-) diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst index 0bfb4c339748..9bc9db8ec651 100644 --- a/Documentation/security/keys/trusted-encrypted.rst +++ b/Documentation/security/keys/trusted-encrypted.rst @@ -350,7 +350,8 @@ Load an encrypted key "evm" from saved blob:: Instantiate an encrypted key "evm" using user-provided decrypted data:: - $ keyctl add encrypted evm "new default user:kmk 32 `cat evm_decrypted_data.blob`" @u + $ evmkey=$(dd if=/dev/urandom bs=1 count=32 | xxd -c32 -p) + $ keyctl add encrypted evm "new default user:kmk 32 $evmkey" @u 794890253 $ keyctl print 794890253 diff --git a/security/keys/encrypted-keys/encrypted.c b/security/keys/encrypted-keys/encrypted.c index e05cfc2e49ae..1e313982af02 100644 --- a/security/keys/encrypted-keys/encrypted.c +++ b/security/keys/encrypted-keys/encrypted.c @@ -627,7 +627,7 @@ static struct encrypted_key_payload *encrypted_key_alloc(struct key *key, pr_err("encrypted key: instantiation of keys using provided decrypted data is disabled since CONFIG_USER_DECRYPTED_DATA is set to false\n"); return ERR_PTR(-EINVAL); } - if (strlen(decrypted_data) != decrypted_datalen) { + if (strlen(decrypted_data) != decrypted_datalen * 2) { pr_err("encrypted key: decrypted data provided does not match decrypted data length provided\n"); return ERR_PTR(-EINVAL); } @@ -791,8 +791,8 @@ static int encrypted_init(struct encrypted_key_payload *epayload, ret = encrypted_key_decrypt(epayload, format, hex_encoded_iv); } else if (decrypted_data) { get_random_bytes(epayload->iv, ivsize); - memcpy(epayload->decrypted_data, decrypted_data, - epayload->decrypted_datalen); + ret = hex2bin(epayload->decrypted_data, decrypted_data, + epayload->decrypted_datalen); } else { get_random_bytes(epayload->iv, ivsize); get_random_bytes(epayload->decrypted_data, epayload->decrypted_datalen);