linux-kernel - Re: [RFC][PATCH 2/5] fsverity: Revalidate built-in signatures at file open

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Message-ID: <YY69NaucW+0t474Q@gmail.com>
Date:   Fri, 12 Nov 2021 11:15:01 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Roberto Sassu <roberto.sassu@...wei.com>
Cc:     tytso@....edu, corbet@....net, viro@...iv.linux.org.uk,
        hughd@...gle.com, akpm@...ux-foundation.org,
        linux-fscrypt@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 2/5] fsverity: Revalidate built-in signatures at
 file open

On Fri, Nov 12, 2021 at 01:44:08PM +0100, Roberto Sassu wrote:
> Fsverity signatures are validated only upon request by the user by setting
> the requirement through procfs or sysctl.
> 
> However, signatures are validated only when the fsverity-related
> initialization is performed on the file. If the initialization happened
> while the signature requirement was disabled, the signature is not
> validated again.

I'm not sure this really matters.  If someone has started using a verity file
before the require_signatures sysctl was set, then there is already a race
condition; this patch doesn't fix that.  Don't you need to set the
require_signatures sysctl early enough anyway?

- Eric