linux-kernel - Re: [PATCH 01/11] evm: Execute evm_inode_init_security() only when the HMAC key is loaded

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Date:   Fri, 21 Aug 2020 14:30:01 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>, mjg59@...gle.com
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 01/11] evm: Execute evm_inode_init_security() only when
 the HMAC key is loaded

Hi Roberto,

Sorry for the delay in reviewing these patches.   Missing from this
patch set is a cover letter with an explanation for grouping these
patches into a patch set, other than for convenience.  In this case, it
would be along the lines that the original use case for EVM portable
and immutable keys support was for a few critical files, not combined
with an EVM encrypted key type.   This patch set more fully integrates
the initial EVM portable and immutable signature support.

On Thu, 2020-06-18 at 18:01 +0200, Roberto Sassu wrote:
> evm_inode_init_security() requires the HMAC key to calculate the HMAC on
> initial xattrs provided by LSMs. Unfortunately, with the evm_key_loaded()
> check, the function continues even if the HMAC key is not loaded
> (evm_key_loaded() returns true also if EVM has been initialized only with a
> public key). If the HMAC key is not loaded, evm_inode_init_security()
> returns an error later when it calls evm_init_hmac().
> 
> Thus, this patch replaces the evm_key_loaded() check with a check of the
> EVM_INIT_HMAC flag in evm_initialized, so that evm_inode_init_security()
> returns 0 instead of an error.
> 
> Cc: stable@...r.kernel.org # 4.5.x
> Fixes: 26ddabfe96b ("evm: enable EVM when X509 certificate is loaded")
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>

Reviewed-by: Mimi Zohar <zohar@...ux.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 0d36259b690d..744c105b48d1 100644
> --- a/security/integrity/evm/evm_main.c
> +++ b/security/integrity/evm/evm_main.c
> @@ -521,7 +521,8 @@ 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);