Re: [PATCH v8 19/24] ima: Move to LSM infrastructure

[Mimi Zohar]

On Thu, 2023-12-14 at 18:08 +0100, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> 
> Move hardcoded IMA function calls (not appraisal-specific functions) from
> various places in the kernel to the LSM infrastructure, by introducing a
> new LSM named 'ima' (at the end of the LSM list and always enabled like
> 'integrity').
> 
> Having IMA before EVM in the Makefile is sufficient to preserve the
> relative order of the new 'ima' LSM in respect to the upcoming 'evm' LSM,
> and thus the order of IMA and EVM function calls as when they were
> hardcoded.
> 
> Make moved functions as static (except ima_post_key_create_or_update(),
> which is not in ima_main.c), and register them as implementation of the
> respective hooks in the new function init_ima_lsm().
> 
> A slight difference is that IMA and EVM functions registered for the
> inode_post_setattr, inode_post_removexattr, path_post_mknod,
> inode_post_create_tmpfile, inode_post_set_acl and inode_post_remove_acl
> won't be executed for private inodes. Since those inodes are supposed to be
> fs-internal, they should not be of interest of IMA or EVM. The S_PRIVATE
> flag is used for anonymous inodes, hugetlbfs, reiserfs xattrs, XFS scrub
> and kernel-internal tmpfs files.
> 
> Conditionally register ima_post_path_mknod() if CONFIG_SECURITY_PATH is
> enabled, otherwise the path_post_mknod hook won't be available.

Up to this point, enabling CONFIG_SECURITY_PATH was not required.  By
making it conditional on CONFIG_SECURITY_PATH, anyone enabling IMA will
also need to enable CONFIG_SECURITY_PATH.  Without it, new files will
not be tagged as a "new" file.

Casey, Paul, how common is it today not to enable CONFIG_SECURITY_PATH?
Will enabling it just for IMA be a problem?

> 
> Also, conditionally register ima_post_key_create_or_update() if
> CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS is enabled.
> 
> Move integrity_kernel_module_request() to IMA and name it
> ima_kernel_module_request(), as only appraisal is affected by the crypto
> subsystem trying to load kernel modules. Conditionally register
> ima_kernel_module_request() if CONFIG_INTEGRITY_ASYMMETRIC_KEYS is
> enabled.

The previous version was so clean. 
Moving integrity_kernel_module_request() to IMA should be a separate
patch, probably a prereq.  Then like the other functions convert it to
an LSM hook.

Please include a line explaning why the original EVM signature is not
affected.

> 
> Finally, add the LSM_ID_IMA case in lsm_list_modules_test.c.
> 
> Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> Acked-by: Chuck Lever <chuck.lever@xxxxxxxxxx>

-- 
thanks,

Mimi