From: Mimi Zohar <zohar@linux.ibm.com>
To: Roberto Sassu <roberto.sassu@huawei.com>, mjg59@google.com
Cc: linux-integrity@vger.kernel.org,
linux-security-module@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
silviu.vlasceanu@huawei.com, stable@vger.kernel.org
Subject: Re: [PATCH v3 03/11] evm: Refuse EVM_ALLOW_METADATA_WRITES only if an HMAC key is loaded
Date: Wed, 02 Dec 2020 16:07:27 -0500 [thread overview]
Message-ID: <a84520e3c7de9c767cbbc17e8ad894525043e211.camel@linux.ibm.com> (raw)
In-Reply-To: <20201111092302.1589-4-roberto.sassu@huawei.com>
On Wed, 2020-11-11 at 10:22 +0100, Roberto Sassu wrote:
> EVM_ALLOW_METADATA_WRITES is an EVM initialization flag that can be set to
> temporarily disable metadata verification until all xattrs/attrs necessary
> to verify an EVM portable signature are copied to the file. This flag is
> cleared when EVM is initialized with an HMAC key, to avoid that the HMAC is
> calculated on unverified xattrs/attrs.
>
> Currently EVM unnecessarily denies setting this flag if EVM is initialized
> with a public key, which is not a concern as it cannot be used to trust
> xattrs/attrs updates. This patch removes this limitation.
>
> Cc: stable@vger.kernel.org # 4.16.x
> Fixes: ae1ba1676b88e ("EVM: Allow userland to permit modification of EVM-protected metadata")
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> ---
> Documentation/ABI/testing/evm | 5 +++--
> security/integrity/evm/evm_secfs.c | 2 +-
> 2 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/ABI/testing/evm b/Documentation/ABI/testing/evm
> index 3c477ba48a31..eb6d70fd6fa2 100644
> --- a/Documentation/ABI/testing/evm
> +++ b/Documentation/ABI/testing/evm
> @@ -49,8 +49,9 @@ Description:
> modification of EVM-protected metadata and
> disable all further modification of policy
>
> - Note that once a key has been loaded, it will no longer be
> - possible to enable metadata modification.
> + Note that once an HMAC key has been loaded, it will no longer
> + be possible to enable metadata modification and, if it is
> + already enabled, it will be disabled.
>
> Until key loading has been signaled EVM can not create
> or validate the 'security.evm' xattr, but returns
> diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c
> index cfc3075769bb..92fe26ace797 100644
> --- a/security/integrity/evm/evm_secfs.c
> +++ b/security/integrity/evm/evm_secfs.c
> @@ -84,7 +84,7 @@ static ssize_t evm_write_key(struct file *file, const char __user *buf,
> * keys are loaded.
> */
> if ((i & EVM_ALLOW_METADATA_WRITES) &&
> - ((evm_initialized & EVM_KEY_MASK) != 0) &&
> + ((evm_initialized & EVM_INIT_HMAC) != 0) &&
> !(evm_initialized & EVM_ALLOW_METADATA_WRITES))
> return -EPERM;
>
If an HMAC key is loaded EVM_ALLOW_METADATA_WRITES should already be
disabled. Testing EVM_ALLOW_METADATA_WRITES shouldn't be needed.
Please update the comment: "Don't allow a request to freshly enable
metadata writes if keys are loaded."
thanks,
Mimi
next prev parent reply other threads:[~2020-12-02 21:10 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-11 9:22 [PATCH v3 00/11] evm: Improve usability of portable signatures Roberto Sassu
2020-11-11 9:22 ` [PATCH v3 01/11] evm: Execute evm_inode_init_security() only when an HMAC key is loaded Roberto Sassu
2020-12-02 17:03 ` Mimi Zohar
2020-11-11 9:22 ` [PATCH v3 02/11] evm: Load EVM key in ima_load_x509() to avoid appraisal Roberto Sassu
2020-12-02 17:27 ` Mimi Zohar
2021-03-01 18:06 ` Mimi Zohar
2020-11-11 9:22 ` [PATCH v3 03/11] evm: Refuse EVM_ALLOW_METADATA_WRITES only if an HMAC key is loaded Roberto Sassu
2020-12-02 21:07 ` Mimi Zohar [this message]
2020-11-11 9:22 ` [PATCH v3 04/11] ima: Move ima_reset_appraise_flags() call to post hooks Roberto Sassu
2020-12-02 11:56 ` Roberto Sassu
2020-12-03 20:43 ` Mimi Zohar
2020-11-11 9:22 ` [PATCH v3 05/11] evm: Introduce evm_status_revalidate() Roberto Sassu
2020-11-11 9:22 ` [PATCH v3 06/11] evm: Ignore INTEGRITY_NOLABEL if no HMAC key is loaded Roberto Sassu
2020-12-03 20:42 ` Mimi Zohar
2020-12-04 8:05 ` Roberto Sassu
2020-12-04 13:04 ` Mimi Zohar
2020-12-04 14:59 ` Roberto Sassu
2020-11-11 9:22 ` [PATCH v3 07/11] evm: Allow xattr/attr operations for portable signatures Roberto Sassu
2020-11-11 9:22 ` [PATCH v3 08/11] evm: Allow setxattr() and setattr() for unmodified metadata Roberto Sassu
2020-11-18 17:58 ` kernel test robot
2020-11-11 9:23 ` [PATCH v3 09/11] ima: Allow imasig requirement to be satisfied by EVM portable signatures Roberto Sassu
2020-11-11 9:23 ` [PATCH v3 10/11] ima: Introduce template field evmsig and write to field sig as fallback Roberto Sassu
2020-11-11 9:23 ` [PATCH v3 11/11] ima: Don't remove security.ima if file must not be appraised Roberto Sassu
2020-12-01 20:52 ` [PATCH v3 00/11] evm: Improve usability of portable signatures Mimi Zohar
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