Re: [PATCH v3 2/9] ima: Always return a file measurement in ima_file_hash()

Mimi Zohar
2022-03-06T19:32:25Z

On Wed, 2022-03-02 at 12:13 +0100, Roberto Sassu wrote:
> __ima_inode_hash() checks if a digest has been already calculated by
> looking for the integrity_iint_cache structure associated to the passed
> inode.
>
> Users of ima_file_hash() (e.g. eBPF) might be interested in obtaining the
> information without having to setup an IMA policy so that the digest is
> always available at the time they call this function.
>
> In addition, they likely expect the digest to be fresh, e.g. recalculated
> by IMA after a file write. Although getting the digest from the
> bprm_committed_creds hook (as in the eBPF test) ensures that the digest is
> fresh, as the IMA hook is executed before that hook, this is not always the
> case (e.g. for the mmap_file hook).
>
> Call ima_collect_measurement() in __ima_inode_hash(), if the file
> descriptor is available (passed by ima_file_hash()) and the digest is not
> available/not fresh, and store the file measurement in a temporary
> integrity_iint_cache structure.
>
> This change does not cause memory usage increase, due to using the
> temporary integrity_iint_cache structure, and due to freeing the
> ima_digest_data structure inside integrity_iint_cache before exiting from
> __ima_inode_hash().
>
> For compatibility reasons, the behavior of ima_inode_hash() remains
> unchanged.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>

The patch itself is fine, but with great hesitancy due to the existing
eBPF integrity gaps and how these functions are planned to be used,

Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>