linux-kernel - Re: [PATCH v9 23/25] evm: Make it independent from 'integrity' LSM

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Date: Mon, 12 Feb 2024 14:13:17 -0500
From: Stefan Berger <stefanb@...ux.ibm.com>
To: Roberto Sassu <roberto.sassu@...weicloud.com>, viro@...iv.linux.org.uk,
        brauner@...nel.org, chuck.lever@...cle.com, jlayton@...nel.org,
        neilb@...e.de, kolga@...app.com, Dai.Ngo@...cle.com, tom@...pey.com,
        paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com,
        zohar@...ux.ibm.com, dmitry.kasatkin@...il.com,
        eric.snowberg@...cle.com, dhowells@...hat.com, jarkko@...nel.org,
        stephen.smalley.work@...il.com, eparis@...isplace.org,
        casey@...aufler-ca.com, shuah@...nel.org, mic@...ikod.net
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
        selinux@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [PATCH v9 23/25] evm: Make it independent from 'integrity' LSM



On 1/15/24 13:18, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@...wei.com>
> 
> Define a new structure for EVM-specific metadata, called evm_iint_cache,
> and embed it in the inode security blob. Introduce evm_iint_inode() to
> retrieve metadata, and register evm_inode_alloc_security() for the
> inode_alloc_security LSM hook, to initialize the structure (before
> splitting metadata, this task was done by iint_init_always()).
> 
> Keep the non-NULL checks after calling evm_iint_inode() except in
> evm_inode_alloc_security(), to take into account inodes for which
> security_inode_alloc() was not called. When using shared metadata,
> obtaining a NULL pointer from integrity_iint_find() meant that the file
> wasn't in the IMA policy. Now, because IMA and EVM use disjoint metadata,
> the EVM status has to be stored for every inode regardless of the IMA
> policy.
> 
> Given that from now on EVM relies on its own metadata, remove the iint
> parameter from evm_verifyxattr(). Also, directly retrieve the iint in
> evm_verify_hmac(), called by both evm_verifyxattr() and
> evm_verify_current_integrity(), since now there is no performance penalty
> in retrieving EVM metadata (constant time).
> 
> Replicate the management of the IMA_NEW_FILE flag, by introducing
> evm_post_path_mknod() and evm_file_release() to respectively set and clear
> the newly introduced flag EVM_NEW_FILE, at the same time IMA does. Like for
> IMA, select CONFIG_SECURITY_PATH when EVM is enabled, to ensure that files
> are marked as new.
> 
> Unlike ima_post_path_mknod(), evm_post_path_mknod() cannot check if a file
> must be appraised. Thus, it marks all affected files. Also, it does not
> clear EVM_NEW_FILE depending on i_version, but that is not a problem
> because IMA_NEW_FILE is always cleared when set in ima_check_last_writer().
> 
> Move the EVM-specific flag EVM_IMMUTABLE_DIGSIG to
> security/integrity/evm/evm.h, since that definition is now unnecessary in
> the common integrity layer.
> 
> Finally, switch to the LSM reservation mechanism for the EVM xattr, and
> consequently decrement by one the number of xattrs to allocate in
> security_inode_init_security().
> 
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>

Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>