From patchwork Wed Aug 2 04:15:03 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Biggers X-Patchwork-Id: 13337611 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 06791110C for ; Wed, 2 Aug 2023 04:15:22 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 355C8C433C7; Wed, 2 Aug 2023 04:15:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1690949722; bh=FwYw1Ys6mearw8rtCro8FNVS+u6xf9XdpTbTQekj87g=; h=From:To:Cc:Subject:Date:From; b=mRdg+NuHMAQD7AwmkHXeiO+PTi0Mx5e7Zk0S0vkZ7vwDNnw7PxJFepqIXyYHYvKgl LtXOf0yCRNyveC9JUWaL2Qqc5RSYwoxWcXpnI+4cgh4/yx3QbgSPWNbsZJvh+dmL3U gxQpBLr3rLOVz8l1EF4ADxzZEh4YFks9xkyrFG6PFG1JW7wZrPXSS1vWiA/mBtws3o 2rv1cVEiVU8XeDHUYQaYbetfl0EHbEAz00OVWi01+chP0MkYNa/hhvwSpyQszO+fXv focjhafydkqJOSbOxBMANzudDhkBhREKLXNmxbm/dUn8ZQzXk5KymNZITBIKTZ3IW3 4B8lEm+bv263Q== From: Eric Biggers To: fsverity@lists.linux.dev Cc: keyrings@vger.kernel.org, Victor Hsieh , stable@vger.kernel.org, Jarkko Sakkinen Subject: [PATCH v2] fsverity: skip PKCS#7 parser when keyring is empty Date: Tue, 1 Aug 2023 21:15:03 -0700 Message-ID: <20230802041503.11530-1-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 Acked-by: Jarkko Sakkinen Signed-off-by: Eric Biggers Reviewed-by: Jarkko Sakkinen --- v2: check keyring and return early before allocating formatted digest fs/verity/signature.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) base-commit: 456ae5fe9b448f44ebe98b391a3bae9c75df465e 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;