linux-kernel - Re: [PATCH v6 03/20] evm: re-release

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Message-ID: <20110602223803.GA23700@mail.hallyn.com>
Date:	Thu, 2 Jun 2011 17:38:03 -0500
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	James Morris <jmorris@...ei.org>,
	David Safford <safford@...son.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <greg@...ah.com>,
	Dmitry Kasatkin <dmitry.s.kasatkin@...il.com>,
	Mimi Zohar <zohar@...ibm.com>
Subject: Re: [PATCH v6 03/20] evm: re-release

Quoting Mimi Zohar (zohar@...ux.vnet.ibm.com):
> EVM protects a file's security extended attributes(xattrs) against integrity
> attacks.  This patchset provides the framework and an initial method.  The
> initial method maintains an HMAC-sha1 value across the security extended
> attributes, storing the HMAC value as the extended attribute 'security.evm'.
> Other methods of validating the integrity of a file's metadata will be posted
> separately (eg. EVM-digital-signatures).
> 
> While this patchset does authenticate the security xattrs, and
> cryptographically binds them to the inode, coming extensions will bind other
> directory and inode metadata for more complete protection.  To help simplify
> the review and upstreaming process, each extension will be posted separately
> (eg. IMA-appraisal, IMA-appraisal-directory).  For a general overview of the
> proposed Linux integrity subsystem, refer to Dave Safford's whitepaper:
> http://downloads.sf.net/project/linux-ima/linux-ima/Integrity_overview.pdf.
> 
> EVM depends on the Kernel Key Retention System to provide it with a
> trusted/encrypted key for the HMAC-sha1 operation. The key is loaded onto the
> root's keyring using keyctl.  Until EVM receives notification that the key has
> been successfully loaded onto the keyring (echo 1 > <securityfs>/evm), EVM can
> not create or validate the 'security.evm' xattr, but returns INTEGRITY_UNKNOWN.
> Loading the key and signaling EVM should be done as early as possible. Normally
> this is done in the initramfs, which has already been measured as part of the
> trusted boot.  For more information on creating and loading existing
> trusted/encrypted keys, refer to Documentation/keys-trusted-encrypted.txt.
> 
> Based on the LSMs enabled, the set of EVM protected security xattrs is defined
> at compile.  EVM adds the following three calls to the existing security hooks:
> evm_inode_setxattr(), evm_inode_post_setxattr(), and evm_inode_removexattr.  To
> initialize and update the 'security.evm' extended attribute, EVM defines three
> calls: evm_inode_post_init(), evm_inode_post_setattr() and
> evm_inode_post_removexattr() hooks.  To verify the integrity of a security
> xattr, EVM exports evm_verifyxattr().
> 
> Changelog v6: (based on Serge Hallyn's review)
> - fix URL in patch description

It's still wrong in Documentation/ABI/testing/evm...

> - remove evm_hmac_size definition
> - use SHA1_DIGEST_SIZE (removed both MAX_DIGEST_SIZE and evm_hmac_size)
> - moved linux include before other includes
> - test for crypto_hash_setkey failure
> - fail earlier for invalid key
> - clear entire encrypted key, even on failure
> - check xattr name length before comparing xattr names

The rest looks good, thanks

Acked-by: Serge Hallyn <serge.hallyn@...onical.com>

-serge
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