From: "Jarkko Sakkinen" <jarkko@kernel.org>
To: "Eric Biggers" <ebiggers@kernel.org>
Cc: <fsverity@lists.linux.dev>, <keyrings@vger.kernel.org>,
"Victor Hsieh" <victorhsieh@google.com>, <stable@vger.kernel.org>
Subject: Re: [PATCH v2] fsverity: skip PKCS#7 parser when keyring is empty
Date: Wed, 02 Aug 2023 10:43:06 +0300 [thread overview]
Message-ID: <CUHW2GFPQ5KC.3SOJM5AMOZ9T0@suppilovahvero> (raw)
In-Reply-To: <20230802043158.GC1543@sol.localdomain>
On Wed Aug 2, 2023 at 7:31 AM EEST, Eric Biggers wrote:
> On Wed, Aug 02, 2023 at 07:27:15AM +0300, Jarkko Sakkinen wrote:
> > On Wed Aug 2, 2023 at 7:15 AM EEST, Eric Biggers wrote:
> > > From: Eric Biggers <ebiggers@google.com>
> > >
> > > If an fsverity builtin signature is given for a file but the
> > > ".fs-verity" keyring is empty, there's no real reason to run the PKCS#7
> > > parser. Skip this to avoid the PKCS#7 attack surface when builtin
> > > signature support is configured into the kernel but is not being used.
> > >
> > > This is a hardening improvement, not a fix per se, but I've added
> > > Fixes and Cc stable to get it out to more users.
> > >
> > > Fixes: 432434c9f8e1 ("fs-verity: support builtin file signatures")
> > > Cc: stable@vger.kernel.org
> > > Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
> > > Signed-off-by: Eric Biggers <ebiggers@google.com>
> > > ---
> > >
> > > v2: check keyring and return early before allocating formatted digest
> > >
> > > fs/verity/signature.c | 15 +++++++++++++++
> > > 1 file changed, 15 insertions(+)
> > >
> > > diff --git a/fs/verity/signature.c b/fs/verity/signature.c
> > > index b95acae64eac6..8f474702aa249 100644
> > > --- a/fs/verity/signature.c
> > > +++ b/fs/verity/signature.c
> > > @@ -62,6 +62,21 @@ int fsverity_verify_signature(const struct fsverity_info *vi,
> > > return 0;
> > > }
> > >
> > > + if (fsverity_keyring->keys.nr_leaves_on_tree == 0) {
> > > + /*
> > > + * The ".fs-verity" keyring is empty, due to builtin signatures
> > > + * being supported by the kernel but not actually being used.
> > > + * In this case, verify_pkcs7_signature() would always return an
> > > + * error, usually ENOKEY. It could also be EBADMSG if the
> > > + * PKCS#7 is malformed, but that isn't very important to
> > > + * distinguish. So, just skip to ENOKEY to avoid the attack
> > > + * surface of the PKCS#7 parser, which would otherwise be
> > > + * reachable by any task able to execute FS_IOC_ENABLE_VERITY.
> > > + */
> > > + fsverity_err(inode, "fs-verity keyring is empty");
> > > + return -ENOKEY;
> > > + }
> > > +
> > > d = kzalloc(sizeof(*d) + hash_alg->digest_size, GFP_KERNEL);
> > > if (!d)
> > > return -ENOMEM;
> > >
> > > base-commit: 456ae5fe9b448f44ebe98b391a3bae9c75df465e
> > > --
> > > 2.41.0
> >
> > Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
> >
> > applied
> >
> > BR, Jarkko
>
> Hi Jarkko, thanks for the review!
>
> I actually intended to take this through the fsverity tree. Is that okay?
>
> BTW, we could actually make this change to verify_pkcs7_signature() itself.
> I wasn't sure it would be appropriate for all callers, though. Any thoughts?
It is OK for me. I just wanted make sure that I don't get yelled let's
say month from now, why I haven't picked it already. That's why the
"more eager" approach :-)
I'll drop it from my master branch today.
BR, Jarkko
prev parent reply other threads:[~2023-08-02 7:46 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-02 4:15 [PATCH v2] fsverity: skip PKCS#7 parser when keyring is empty Eric Biggers
2023-08-02 4:27 ` Jarkko Sakkinen
2023-08-02 4:31 ` Eric Biggers
2023-08-02 7:43 ` Jarkko Sakkinen [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CUHW2GFPQ5KC.3SOJM5AMOZ9T0@suppilovahvero \
--to=jarkko@kernel.org \
--cc=ebiggers@kernel.org \
--cc=fsverity@lists.linux.dev \
--cc=keyrings@vger.kernel.org \
--cc=stable@vger.kernel.org \
--cc=victorhsieh@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).