linux-ext4 - Re: [PATCH] fsverity: don't check builtin signatures when require

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Message-ID: <CAMw=ZnS5mXpQYtGHEK7-Q-VEojhooXiQVsGPT3e8NCW8uxnWyA@mail.gmail.com>
Date:   Sat, 17 Dec 2022 02:06:04 +0000
From:   Luca Boccassi <bluca@...ian.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-fscrypt@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-btrfs@...r.kernel.org, linux-integrity@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] fsverity: don't check builtin signatures when require_signatures=0

On Fri, 16 Dec 2022 at 21:06, Eric Biggers <ebiggers@...nel.org> wrote:
>
> On Thu, Dec 08, 2022 at 08:42:56PM +0000, Luca Boccassi wrote:
> > On Thu, 8 Dec 2022 at 03:35, Eric Biggers <ebiggers@...nel.org> wrote:
> > >
> > > From: Eric Biggers <ebiggers@...gle.com>
> > >
> > > An issue that arises when migrating from builtin signatures to userspace
> > > signatures is that existing files that have builtin signatures cannot be
> > > opened unless either CONFIG_FS_VERITY_BUILTIN_SIGNATURES is disabled or
> > > the signing certificate is left in the .fs-verity keyring.
> > >
> > > Since builtin signatures provide no security benefit when
> > > fs.verity.require_signatures=0 anyway, let's just skip the signature
> > > verification in this case.
> > >
> > > Fixes: 432434c9f8e1 ("fs-verity: support builtin file signatures")
> > > Cc: <stable@...r.kernel.org> # v5.4+
> > > Signed-off-by: Eric Biggers <ebiggers@...gle.com>
> > > ---
> > >  fs/verity/signature.c | 18 ++++++++++++++++--
> > >  1 file changed, 16 insertions(+), 2 deletions(-)
> >
> > Acked-by: Luca Boccassi <bluca@...ian.org>
>
> So if I can't apply
> https://lore.kernel.org/linux-fscrypt/20221208033548.122704-1-ebiggers@kernel.org
> ("fsverity: mark builtin signatures as deprecated") due to IPE, wouldn't I not
> be able to apply this patch either?  Surely IPE isn't depending on
> fs.verity.require_signatures=1, given that it enforces the policy itself?

I'm not sure what you mean? Skipping verification when this syscfg is
disabled makes sense to me, as you noted it doesn't serve any purpose
in that case.

Kind regards,
Luca Boccassi