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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C36A4C433EF for ; Tue, 8 Mar 2022 11:54:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346612AbiCHLzb (ORCPT ); Tue, 8 Mar 2022 06:55:31 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55630 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235676AbiCHLz3 (ORCPT ); Tue, 8 Mar 2022 06:55:29 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8BB8F2DD5F; Tue, 8 Mar 2022 03:54:32 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 02D12616B4; Tue, 8 Mar 2022 11:54:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0E320C340EE; Tue, 8 Mar 2022 11:54:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1646740471; bh=mK13UO2icdJkbKzDbJRR7VE/cOk6rGlpu6tEY0bGCuI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Re5QDj7KRYzTymY4POCxVl1W2LAH0TjcmZxoB7Lcljws/4CY5LeietEgW+tc6LQ+S iEDz677lvA1j7kmfIoqfKmPa6Hury9ctUNCbbdkWgNYiR8vMexjRRBCKxXMwAvIrMd r4nrMUUZWzdOlzGP56ssPqA4ZqGCiEiOFibWz8STmwMRuF/FCDiFMaFnB6V2aZjFfY vZHLYQJ7a2GAk2LM0Q8tGJ63WFN4b9hLuLGFe9aXqKjJcMtxNvFapkaomSWGx75JhS hk2bDSCmqbjAsjtsygHOFwRdfHqTi8Kwoz6hQHGpEum45KLH7qoxv7a66TY5iCYe40 X7BOwDpy4dnNw== Date: Tue, 8 Mar 2022 13:53:50 +0200 From: Jarkko Sakkinen To: =?iso-8859-1?Q?Micka=EBl_Sala=FCn?= Cc: David Howells , David Woodhouse , "David S . Miller" , Eric Snowberg , Herbert Xu , James Morris , =?iso-8859-1?Q?Micka=EBl_Sala=FCn?= , Mimi Zohar , "Serge E . Hallyn" , Tyler Hicks , keyrings@vger.kernel.org, linux-crypto@vger.kernel.org, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org Subject: Re: [PATCH v8 5/5] certs: Allow root user to append signed hashes to the blacklist keyring Message-ID: References: <20210712170313.884724-1-mic@digikod.net> <20210712170313.884724-6-mic@digikod.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20210712170313.884724-6-mic@digikod.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 12, 2021 at 07:03:13PM +0200, Mickaël Salaün wrote: > From: Mickaël Salaün > > Add a kernel option SYSTEM_BLACKLIST_AUTH_UPDATE to enable the root user > to dynamically add new keys to the blacklist keyring. This enables to > invalidate new certificates, either from being loaded in a keyring, or > from being trusted in a PKCS#7 certificate chain. This also enables to > add new file hashes to be denied by the integrity infrastructure. > > Being able to untrust a certificate which could have normaly been > trusted is a sensitive operation. This is why adding new hashes to the > blacklist keyring is only allowed when these hashes are signed and > vouched by the builtin trusted keyring. A blacklist hash is stored as a > key description. The PKCS#7 signature of this description must be > provided as the key payload. > > Marking a certificate as untrusted should be enforced while the system > is running. It is then forbiden to remove such blacklist keys. > > Update blacklist keyring, blacklist key and revoked certificate access rights: > * allows the root user to search for a specific blacklisted hash, which > make sense because the descriptions are already viewable; > * forbids key update (blacklist and asymmetric ones); > * restricts kernel rights on the blacklist keyring to align with the > root user rights. > > See help in tools/certs/print-cert-tbs-hash.sh . > > Cc: David Howells > Cc: David Woodhouse > Cc: Eric Snowberg > Cc: Jarkko Sakkinen > Signed-off-by: Mickaël Salaün > Link: https://lore.kernel.org/r/20210712170313.884724-6-mic@digikod.net > --- > > Changes since v6: > * Rebase on keys-cve-2020-26541-v3: commit ebd9c2ae369a ("integrity: > Load mokx variables into the blacklist keyring"). > > Changes since v5: > * Rebase on keys-next, fix Kconfig conflict, and update the asymmetric > key rights added to the blacklist keyring by the new > add_key_to_revocation_list(): align with blacklist key rights by > removing KEY_POS_WRITE as a safeguard, and add > KEY_ALLOC_BYPASS_RESTRICTION to not be subject to > restrict_link_for_blacklist() that only allows blacklist key types to > be added to the keyring. > * Change the return code for restrict_link_for_blacklist() from -EPERM > to -EOPNOTSUPP to align with asymmetric key keyrings. > > Changes since v3: > * Update commit message for print-cert-tbs-hash.sh . > > Changes since v2: > * Add comment for blacklist_key_instantiate(). > --- > certs/Kconfig | 10 +++++ > certs/blacklist.c | 96 ++++++++++++++++++++++++++++++++++++----------- > 2 files changed, 85 insertions(+), 21 deletions(-) > > diff --git a/certs/Kconfig b/certs/Kconfig > index 0fbe184ceca5..e0e524b7eff9 100644 > --- a/certs/Kconfig > +++ b/certs/Kconfig > @@ -103,4 +103,14 @@ config SYSTEM_REVOCATION_KEYS > containing X.509 certificates to be included in the default blacklist > keyring. > > +config SYSTEM_BLACKLIST_AUTH_UPDATE > + bool "Allow root to add signed blacklist keys" > + depends on SYSTEM_BLACKLIST_KEYRING > + depends on SYSTEM_DATA_VERIFICATION > + help > + If set, provide the ability to load new blacklist keys at run time if > + they are signed and vouched by a certificate from the builtin trusted > + keyring. The PKCS#7 signature of the description is set in the key > + payload. Blacklist keys cannot be removed. > + > endmenu > diff --git a/certs/blacklist.c b/certs/blacklist.c > index b254c87ceb3a..486ce0dd8e9c 100644 > --- a/certs/blacklist.c > +++ b/certs/blacklist.c > @@ -15,6 +15,7 @@ > #include > #include > #include > +#include > #include > #include "blacklist.h" > #include "common.h" > @@ -26,6 +27,9 @@ > */ > #define MAX_HASH_LEN 128 > > +#define BLACKLIST_KEY_PERM (KEY_POS_SEARCH | KEY_POS_VIEW | \ > + KEY_USR_SEARCH | KEY_USR_VIEW) > + > static const char tbs_prefix[] = "tbs"; > static const char bin_prefix[] = "bin"; > > @@ -80,19 +84,51 @@ static int blacklist_vet_description(const char *desc) > return 0; > } > > -/* > - * The hash to be blacklisted is expected to be in the description. There will > - * be no payload. > - */ > -static int blacklist_preparse(struct key_preparsed_payload *prep) > +static int blacklist_key_instantiate(struct key *key, > + struct key_preparsed_payload *prep) > { > - if (prep->datalen > 0) > - return -EINVAL; > - return 0; > +#ifdef CONFIG_SYSTEM_BLACKLIST_AUTH_UPDATE > + int err; > +#endif > + > + /* Sets safe default permissions for keys loaded by user space. */ > + key->perm = BLACKLIST_KEY_PERM; > + > + /* > + * Skips the authentication step for builtin hashes, they are not > + * signed but still trusted. > + */ > + if (key->flags & (1 << KEY_FLAG_BUILTIN)) > + goto out; > + > +#ifdef CONFIG_SYSTEM_BLACKLIST_AUTH_UPDATE > + /* > + * Verifies the description's PKCS#7 signature against the builtin > + * trusted keyring. > + */ > + err = verify_pkcs7_signature(key->description, > + strlen(key->description), prep->data, prep->datalen, > + NULL, VERIFYING_UNSPECIFIED_SIGNATURE, NULL, NULL); > + if (err) > + return err; > +#else > + /* > + * It should not be possible to come here because the keyring doesn't > + * have KEY_USR_WRITE and the only other way to call this function is > + * for builtin hashes. > + */ > + WARN_ON_ONCE(1); > + return -EPERM; > +#endif > + > +out: > + return generic_key_instantiate(key, prep); > } > > -static void blacklist_free_preparse(struct key_preparsed_payload *prep) > +static int blacklist_key_update(struct key *key, > + struct key_preparsed_payload *prep) > { > + return -EPERM; > } > > static void blacklist_describe(const struct key *key, struct seq_file *m) > @@ -103,9 +139,8 @@ static void blacklist_describe(const struct key *key, struct seq_file *m) > static struct key_type key_type_blacklist = { > .name = "blacklist", > .vet_description = blacklist_vet_description, > - .preparse = blacklist_preparse, > - .free_preparse = blacklist_free_preparse, > - .instantiate = generic_key_instantiate, > + .instantiate = blacklist_key_instantiate, > + .update = blacklist_key_update, > .describe = blacklist_describe, > }; > > @@ -154,8 +189,7 @@ static int mark_raw_hash_blacklisted(const char *hash) > hash, > NULL, > 0, > - ((KEY_POS_ALL & ~KEY_POS_SETATTR) | > - KEY_USR_VIEW), > + BLACKLIST_KEY_PERM, > KEY_ALLOC_NOT_IN_QUOTA | > KEY_ALLOC_BUILT_IN); > if (IS_ERR(key)) { > @@ -232,8 +266,10 @@ int add_key_to_revocation_list(const char *data, size_t size) > NULL, > data, > size, > - ((KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_VIEW), > - KEY_ALLOC_NOT_IN_QUOTA | KEY_ALLOC_BUILT_IN); > + KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH > + | KEY_USR_VIEW, > + KEY_ALLOC_NOT_IN_QUOTA | KEY_ALLOC_BUILT_IN > + | KEY_ALLOC_BYPASS_RESTRICTION); > > if (IS_ERR(key)) { > pr_err("Problem with revocation key (%ld)\n", PTR_ERR(key)); > @@ -260,25 +296,43 @@ int is_key_on_revocation_list(struct pkcs7_message *pkcs7) > } > #endif > > +static int restrict_link_for_blacklist(struct key *dest_keyring, > + const struct key_type *type, const union key_payload *payload, > + struct key *restrict_key) > +{ > + if (type == &key_type_blacklist) > + return 0; > + return -EOPNOTSUPP; > +} > + > /* > * Initialise the blacklist > */ > static int __init blacklist_init(void) > { > const char *const *bl; > + struct key_restriction *restriction; > > if (register_key_type(&key_type_blacklist) < 0) > panic("Can't allocate system blacklist key type\n"); > > + restriction = kzalloc(sizeof(*restriction), GFP_KERNEL); > + if (!restriction) > + panic("Can't allocate blacklist keyring restriction\n"); This prevents me from taking this to my pull request. In moderns standards, no new BUG_ON(), panic() etc. should never added to the kernel. I missed this in my review. This should rather be e.g. restriction = kzalloc(sizeof(*restriction), GFP_KERNEL); if (!restriction) { pr_err("Can't allocate blacklist keyring restriction\n"); return 0; } Unfortunately I need to drop this patch set, because adding new panic() is simply a no-go. BR, Jarkko