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 AE12E4C8F for ; Wed, 2 Aug 2023 07:43:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 82271C433CA; Wed, 2 Aug 2023 07:43:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1690962191; bh=uliLFqbyfAo8ZWX8SKLjPrgv/IXg23iwEndg0QZY4NE=; h=Date:Cc:Subject:From:To:References:In-Reply-To:From; b=BBV4dJjCqOVG5TcNj0S/19UTgWEwPQmIUTarzCPUbgVhaALhKERTC0cYDc+r0xaLy IC4n2ymPEsesVEKYK78KfLCJozVt4XNCYvASWYdZCVcini0GY8qVDbpvaM7OsYRxC+ 7v90t9YDyV0EBdFkYNKUyOXKRQWqG1JL3APDJe5Dmk6QoOZIg91zohVYlz+6pSfuuJ Dkn94uDQTaBMdy1ThqVrpM0XR23HKdY8vsQWXYfFRInEWGE5VJYcu4jEQYYoOSu5bZ 3BLFiuTdiZm5cE//ujN+IimL0uisdPWLnV4zUfwjdXKkujOVvc/CnLBuN0TVkKrRNd 8xgimMD7NETWA== 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 10:43:06 +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> <20230802043158.GC1543@sol.localdomain> 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 > > > > > > 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 fsverit= y_info *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 > >=20 > > Reviewed-by: Jarkko Sakkinen > >=20 > > applied > >=20 > > 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() itsel= f. > I wasn't sure it would be appropriate for all callers, though. Any thoug= hts? 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