netdev - Re: [PATCH] ima: Calculate digest in ima_inode

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Date:   Tue, 15 Feb 2022 06:16:52 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "andrii@...nel.org" <andrii@...nel.org>,
        "kpsingh@...nel.org" <kpsingh@...nel.org>,
        Florent Revest <revest@...omium.org>
Cc:     "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ima: Calculate digest in ima_inode_hash() if not
 available

On Tue, 2022-02-15 at 08:00 +0000, Roberto Sassu wrote:
> > >
> > > I found that just checking that iint->ima_hash is not NULL is not enough
> > > (ima_inode_hash() might still return the old digest after a file write).
> > > Should I replace that check with !(iint->flags & IMA_COLLECTED)?
> > > Or should I do only for ima_file_hash() and recalculate the digest
> > > if necessary?
> > 
> > Updating the file hash after each write would really impact IMA
> > performance.  If you really want to detect any file change, no matter
> > how frequently it occurs, your best bet would be to track i_generation
> > and i_version.  Stefan is already adding "i_generation" for IMA
> > namespacing.
> 
> I just wanted the ability to get a fresh digest after a file opened
> for writing is closed. Since in my use case I would not use an IMA
> policy, that would not be a problem.

As I recall, the __fput() delay was to prevent locking ordering issues
- inode, iint.

-- 
thanks,

Mimi