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Date: Wed, 07 Feb 2024 22:18:54 -0500
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From: Paul Moore <paul@paul-moore.com>
To: Roberto Sassu <roberto.sassu@huaweicloud.com>, viro@zeniv.linux.org.uk, brauner@kernel.org, chuck.lever@oracle.com, jlayton@kernel.org, neilb@suse.de, kolga@netapp.com, Dai.Ngo@oracle.com, tom@talpey.com, jmorris@namei.org, serge@hallyn.com, zohar@linux.ibm.com, dmitry.kasatkin@gmail.com, eric.snowberg@oracle.com, dhowells@redhat.com, jarkko@kernel.org, stephen.smalley.work@gmail.com, eparis@parisplace.org, casey@schaufler-ca.com, shuah@kernel.org, mic@digikod.net
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-security-module@vger.kernel.org, linux-integrity@vger.kernel.org, keyrings@vger.kernel.org, selinux@vger.kernel.org, linux-kselftest@vger.kernel.org, Roberto Sassu <roberto.sassu@huawei.com>
Subject: Re: [PATCH v9 23/25] evm: Make it independent from 'integrity' LSM
References: <20240115181809.885385-24-roberto.sassu@huaweicloud.com>
In-Reply-To: <20240115181809.885385-24-roberto.sassu@huaweicloud.com>

On Jan 15, 2024 Roberto Sassu <roberto.sassu@huaweicloud.com> wrote:
> 
> 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@huawei.com>
> Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>
> ---
>  include/linux/evm.h                   |  8 +--
>  security/integrity/evm/Kconfig        |  1 +
>  security/integrity/evm/evm.h          | 19 +++++++
>  security/integrity/evm/evm_crypto.c   |  4 +-
>  security/integrity/evm/evm_main.c     | 76 ++++++++++++++++++++-------
>  security/integrity/ima/ima_appraise.c |  2 +-
>  security/integrity/integrity.h        |  1 -
>  security/security.c                   |  4 +-
>  8 files changed, 83 insertions(+), 32 deletions(-)

Acked-by: Paul Moore <paul@paul-moore.com>

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