From patchwork Sun Aug 20 17:32:36 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Biggers X-Patchwork-Id: 13358855 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 92EE6256D for ; Sun, 20 Aug 2023 17:33:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B3E6BC433C8; Sun, 20 Aug 2023 17:33:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1692552794; bh=WENwwukqvqLnh0i70wqLdjnC9+i3wzyAPZzzsBwu9GM=; h=From:To:Cc:Subject:Date:From; b=eK/Pj2PDOw6jbR+ynm+yECSoWnkZi9Rc3RDtiMFJFwqkdk18F5shl80G1K3gaUhh1 hEdJriIWbIxefsn5Jcn1ai/Fe0pFfibiEBRlVdz+N/UhVfJJtpr48OkuO5vC5tD9z0 7nf3mWpQwAgQ6wJCYC3bvPhwyqfrpej6as3YI4/sdZZMpMHSFb98waMAS7F3HY+hOg gFLw65u0yb4zhJ85XhLme3By0rS6Ql7Ae1rlUHn9+/robFW7syDT/sR1iYnb2EmVUV 7FNeTRfgsJwiMrTBahR5RywGoXA7ezpYINelM8MCdAkM5DB0hpu1ThYtdmfUdvnFvR +DT9QDvFLjmjA== From: Eric Biggers To: fsverity@lists.linux.dev Cc: Victor Hsieh , stable@vger.kernel.org, Jarkko Sakkinen Subject: [PATCH v3] fsverity: skip PKCS#7 parser when keyring is empty Date: Sun, 20 Aug 2023 10:32:36 -0700 Message-ID: <20230820173237.2579-1-ebiggers@kernel.org> X-Mailer: git-send-email 2.41.0 Precedence: bulk X-Mailing-List: fsverity@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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 Reviewed-by: Jarkko Sakkinen Signed-off-by: Eric Biggers Reviewed-by: Jarkko Sakkinen --- v3: improve the error message slightly v2: check keyring and return early before allocating formatted digest fs/verity/signature.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) base-commit: 456ae5fe9b448f44ebe98b391a3bae9c75df465e diff --git a/fs/verity/signature.c b/fs/verity/signature.c index b95acae64eac6..90c07573dd77b 100644 --- a/fs/verity/signature.c +++ b/fs/verity/signature.c @@ -55,20 +55,36 @@ int fsverity_verify_signature(const struct fsverity_info *vi, if (sig_size == 0) { if (fsverity_require_signatures) { fsverity_err(inode, "require_signatures=1, rejecting unsigned file!"); return -EPERM; } 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, rejecting signed file!"); + return -ENOKEY; + } + d = kzalloc(sizeof(*d) + hash_alg->digest_size, GFP_KERNEL); if (!d) return -ENOMEM; memcpy(d->magic, "FSVerity", 8); d->digest_algorithm = cpu_to_le16(hash_alg - fsverity_hash_algs); d->digest_size = cpu_to_le16(hash_alg->digest_size); memcpy(d->digest, vi->file_digest, hash_alg->digest_size); err = verify_pkcs7_signature(d, sizeof(*d) + hash_alg->digest_size, signature, sig_size, fsverity_keyring,