linux-kernel - Re: [PATCH v2 08/12] evm: Allow xattr/attr operations for portable signatures if check fails

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <03e55547ff7c8725a73f60c460deb13a5b135531.camel@linux.ibm.com>
Date:   Thu, 17 Sep 2020 08:32:16 -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, silviu.vlasceanu@...wei.com
Subject: Re: [PATCH v2 08/12] evm: Allow xattr/attr operations for portable
 signatures if check fails

Hi Roberto,

"if check fails" in the Subject line is unnecessary.

On Fri, 2020-09-04 at 11:26 +0200, Roberto Sassu wrote:
> If files with portable signatures are copied from one location to another
> or are extracted from an archive, verification can temporarily fail until
> all xattrs/attrs are set in the destination. Only portable signatures may
> be moved or copied from one file to another, as they don't depend on
> system-specific information such as the inode generation. Instead portable
> signatures must include security.ima.
> 
> Unlike other security.evm types, EVM portable signatures are also
> immutable. Thus, it wouldn't be a problem to allow xattr/attr operations
> when verification fails, as portable signatures will never be replaced with
> an HMAC on possibly corrupted xattrs/attrs.
> 
> This patch first introduces a new integrity status called
> INTEGRITY_FAIL_IMMUTABLE, that allows callers of
> evm_verify_current_integrity() to detect that a portable signature didn't
> pass verification and then adds an exception in evm_protect_xattr() and
> evm_inode_setattr() for this status and returns 0 instead of -EPERM.
> 
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>

< snip >

> diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
> index 05be1ad3e6f3..a5dab1ac9374 100644
> --- a/security/integrity/evm/evm_main.c
> +++ b/security/integrity/evm/evm_main.c
> 
> @@ -358,6 +364,12 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
>  				    -EPERM, 0);
>  	}
>  out:
> +	/* Writing other xattrs is safe for portable signatures, as portable
> +	 * signatures are immutable and can never be updated.
> +	 */

This is the second time I'm seeing this comment format style.   Why? 
What changed?

Mimi

> +	if (evm_status == INTEGRITY_FAIL_IMMUTABLE)
> +		return 0;
> +
>  	if (evm_status != INTEGRITY_PASS)
>  		integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
>  				    dentry->d_name.name, "appraise_metadata",