From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 12DC6111B for ; Wed, 2 Aug 2023 04:27:19 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CB901C433C7; Wed, 2 Aug 2023 04:27:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1690950439; bh=hX4+BBNpY6v9V9yZmshvQoS2ubWChKYDj6zUT1dKWf0=; h=Date:Cc:Subject:From:To:References:In-Reply-To:From; b=bSxZK9xs07htwRlGuKQb9U2jFQkdd+JKtZYkj+yJEcR44l8EqDG1BjPOtF+4W2jn3 wykaCI70IJb3VLGc85XnN8GzZXv6RbmV5T5CJ4t7SQ3WWZUArbOrtG2nZUMnZ4LOd9 UagH0QAmYhqQxETcZlp1l4L1URn4Foxi+Fh3+nBzHop3PgHCrHIK9XklKMUgIetOGH oRGyd7XXqlxvrhOhFpM5FkG6nkW4P737UzLaOxq6rrtFfhlaLIsMmVN8q3hqNpe6mn zSQwVjbhZn4K2TvzW3Fk4EJzLjXfYZk6Wv5tOPu2aNKG6LTQ/QIq19rMqZOHPO5rQA lONsz3hkckJHg== Precedence: bulk X-Mailing-List: fsverity@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Wed, 02 Aug 2023 07:27:15 +0300 Message-Id: Cc: , "Victor Hsieh" , Subject: Re: [PATCH v2] fsverity: skip PKCS#7 parser when keyring is empty From: "Jarkko Sakkinen" To: "Eric Biggers" , X-Mailer: aerc 0.14.0 References: <20230802041503.11530-1-ebiggers@kernel.org> In-Reply-To: <20230802041503.11530-1-ebiggers@kernel.org> On Wed Aug 2, 2023 at 7:15 AM EEST, Eric Biggers wrote: > From: Eric Biggers > > 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 > Signed-off-by: Eric Biggers > --- > > 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_in= fo *vi, > return 0; > } > =20 > + if (fsverity_keyring->keys.nr_leaves_on_tree =3D=3D 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 =3D kzalloc(sizeof(*d) + hash_alg->digest_size, GFP_KERNEL); > if (!d) > return -ENOMEM; > > base-commit: 456ae5fe9b448f44ebe98b391a3bae9c75df465e > --=20 > 2.41.0 Reviewed-by: Jarkko Sakkinen applied BR, Jarkko