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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 01/11] evm: Execute evm_inode_init_security() only when an HMAC key is loaded
Date: Wed, 02 Dec 2020 12:03:34 -0500	[thread overview]
Message-ID: <c90746b88ff93402910f03a02ffb555bb781578d.camel@linux.ibm.com> (raw)
In-Reply-To: <20201111092302.1589-2-roberto.sassu@huawei.com>

On Wed, 2020-11-11 at 10:22 +0100, Roberto Sassu wrote:
> evm_inode_init_security() requires an HMAC key to calculate the HMAC on
> initial xattrs provided by LSMs. However, it checks generically whether a
> key has been loaded, including also public keys, which is not correct as
> public keys are not suitable to calculate the HMAC.
> 
> Originally, support for signature verification was introduced to verify a
> possibly immutable initial ram disk, when no new files are created, and to
> switch to HMAC for the root filesystem. By that time, an HMAC key should
> have been loaded and usable to calculate HMACs for new files.
> 
> More recently support for requiring an HMAC key was removed from the
> kernel, so that signature verification can be used alone. Since this is a
> legitimate use case, evm_inode_init_security() should not return an error
> when no HMAC key has been loaded.
> 
> This patch fixes this problem by replacing the evm_key_loaded() check with
> a check of the EVM_INIT_HMAC flag in evm_initialized.
> 
> Cc: stable@vger.kernel.org # 4.5.x
> Fixes: 26ddabfe96b ("evm: enable EVM when X509 certificate is loaded")
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
> ---
>  security/integrity/evm/evm_main.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
> index 76d19146d74b..001e001eae01 100644
> --- a/security/integrity/evm/evm_main.c
> +++ b/security/integrity/evm/evm_main.c
> @@ -530,7 +530,8 @@ int evm_inode_init_security(struct inode *inode,
>  	struct evm_xattr *xattr_data;
>  	int rc;
>  
> -	if (!evm_key_loaded() || !evm_protected_xattr(lsm_xattr->name))
> +	if (!(evm_initialized & EVM_INIT_HMAC) ||
> +	    !evm_protected_xattr(lsm_xattr->name))
>  		return 0;
>  
>  	xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);

Let's update the function description to make it explicit.  Something
like: "evm_inode_init_security - initializes security.evm HMAC value"

Mimi




  reply	other threads:[~2020-12-02 17:04 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 [this message]
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
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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