linux-kernel - Re: [PATCH v3 2/9] ima: Always return a file measurement in ima_file

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Message-ID: <1616eae810986a6570f472b3fa7eb099b3134b4a.camel@linux.ibm.com>
Date:   Sun, 06 Mar 2022 14:31:47 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>, shuah@...nel.org,
        ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        yhs@...com, kpsingh@...nel.org, revest@...omium.org,
        gregkh@...uxfoundation.org
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kselftest@...r.kernel.org, bpf@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/9] ima: Always return a file measurement in
 ima_file_hash()

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@...wei.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@...ux.ibm.com>