lkml.org 
[lkml]   [2021]   [Mar]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH v7 1/5] tools/certs: Add print-cert-tbs-hash.sh
    From
    Date

    > On Mar 12, 2021, at 10:12 AM, Mickaël Salaün <mic@digikod.net> wrote:
    >
    > From: Mickaël Salaün <mic@linux.microsoft.com>
    >
    > Add a new helper print-cert-tbs-hash.sh to generate a TBSCertificate
    > hash from a given certificate. This is useful to generate a blacklist
    > key description used to forbid loading a specific certificate in a
    > keyring, or to invalidate a certificate provided by a PKCS#7 file.
    >
    > This kind of hash formatting is required to populate the file pointed
    > out by CONFIG_SYSTEM_BLACKLIST_HASH_LIST, but only the kernel code was
    > available to understand how to effectively create such hash.
    >
    > Cc: David Howells <dhowells@redhat.com>
    > Cc: David Woodhouse <dwmw2@infradead.org>
    > Cc: Eric Snowberg <eric.snowberg@oracle.com>
    > Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
    > Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
    > Link: https://lore.kernel.org/r/20210312171232.2681989-2-mic@digikod.net

    Tested-by: Eric Snowberg <eric.snowberg@oracle.com>

    > ---
    >
    > Changes since v5:
    > * Add Reviewed-by Jarkko.
    >
    > Changes since v3:
    > * Explain in the commit message that this kind of formating is not new
    > but it wasn't documented.
    >
    > Changes since v1:
    > * Fix typo.
    > * Use "if" block instead of "||" .
    > ---
    > MAINTAINERS | 1 +
    > tools/certs/print-cert-tbs-hash.sh | 91 ++++++++++++++++++++++++++++++
    > 2 files changed, 92 insertions(+)
    > create mode 100755 tools/certs/print-cert-tbs-hash.sh
    >
    > diff --git a/MAINTAINERS b/MAINTAINERS
    > index 00836f6452f0..773a362e807f 100644
    > --- a/MAINTAINERS
    > +++ b/MAINTAINERS
    > @@ -4120,6 +4120,7 @@ F: Documentation/admin-guide/module-signing.rst
    > F: certs/
    > F: scripts/extract-cert.c
    > F: scripts/sign-file.c
    > +F: tools/certs/
    >
    > CFAG12864B LCD DRIVER
    > M: Miguel Ojeda Sandonis <miguel.ojeda.sandonis@gmail.com>
    > diff --git a/tools/certs/print-cert-tbs-hash.sh b/tools/certs/print-cert-tbs-hash.sh
    > new file mode 100755
    > index 000000000000..c93df5387ec9
    > --- /dev/null
    > +++ b/tools/certs/print-cert-tbs-hash.sh
    > @@ -0,0 +1,91 @@
    > +#!/bin/bash
    > +# SPDX-License-Identifier: GPL-2.0
    > +#
    > +# Copyright © 2020, Microsoft Corporation. All rights reserved.
    > +#
    > +# Author: Mickaël Salaün <mic@linux.microsoft.com>
    > +#
    > +# Compute and print the To Be Signed (TBS) hash of a certificate. This is used
    > +# as description of keys in the blacklist keyring to identify certificates.
    > +# This output should be redirected, without newline, in a file (hash0.txt) and
    > +# signed to create a PKCS#7 file (hash0.p7s). Both of these files can then be
    > +# loaded in the kernel with.
    > +#
    > +# Exemple on a workstation:
    > +# ./print-cert-tbs-hash.sh certificate-to-invalidate.pem > hash0.txt
    > +# openssl smime -sign -in hash0.txt -inkey builtin-private-key.pem \
    > +# -signer builtin-certificate.pem -certfile certificate-chain.pem \
    > +# -noattr -binary -outform DER -out hash0.p7s
    > +#
    > +# Exemple on a managed system:
    > +# keyctl padd blacklist "$(< hash0.txt)" %:.blacklist < hash0.p7s
    > +
    > +set -u -e -o pipefail
    > +
    > +CERT="${1:-}"
    > +BASENAME="$(basename -- "${BASH_SOURCE[0]}")"
    > +
    > +if [ $# -ne 1 ] || [ ! -f "${CERT}" ]; then
    > + echo "usage: ${BASENAME} <certificate>" >&2
    > + exit 1
    > +fi
    > +
    > +# Checks that it is indeed a certificate (PEM or DER encoded) and exclude the
    > +# optional PEM text header.
    > +if ! PEM="$(openssl x509 -inform DER -in "${CERT}" 2>/dev/null || openssl x509 -in "${CERT}")"; then
    > + echo "ERROR: Failed to parse certificate" >&2
    > + exit 1
    > +fi
    > +
    > +# TBSCertificate starts at the second entry.
    > +# Cf. https://tools.ietf.org/html/rfc3280#section-4.1
    > +#
    > +# Exemple of first lines printed by openssl asn1parse:
    > +# 0:d=0 hl=4 l= 763 cons: SEQUENCE
    > +# 4:d=1 hl=4 l= 483 cons: SEQUENCE
    > +# 8:d=2 hl=2 l= 3 cons: cont [ 0 ]
    > +# 10:d=3 hl=2 l= 1 prim: INTEGER :02
    > +# 13:d=2 hl=2 l= 20 prim: INTEGER :3CEB2CB8818D968AC00EEFE195F0DF9665328B7B
    > +# 35:d=2 hl=2 l= 13 cons: SEQUENCE
    > +# 37:d=3 hl=2 l= 9 prim: OBJECT :sha256WithRSAEncryption
    > +RANGE_AND_DIGEST_RE='
    > +2s/^\s*\([0-9]\+\):d=\s*[0-9]\+\s\+hl=\s*[0-9]\+\s\+l=\s*\([0-9]\+\)\s\+cons:\s*SEQUENCE\s*$/\1 \2/p;
    > +7s/^\s*[0-9]\+:d=\s*[0-9]\+\s\+hl=\s*[0-9]\+\s\+l=\s*[0-9]\+\s\+prim:\s*OBJECT\s*:\(.*\)$/\1/p;
    > +'
    > +
    > +RANGE_AND_DIGEST=($(echo "${PEM}" | \
    > + openssl asn1parse -in - | \
    > + sed -n -e "${RANGE_AND_DIGEST_RE}"))
    > +
    > +if [ "${#RANGE_AND_DIGEST[@]}" != 3 ]; then
    > + echo "ERROR: Failed to parse TBSCertificate." >&2
    > + exit 1
    > +fi
    > +
    > +OFFSET="${RANGE_AND_DIGEST[0]}"
    > +END="$(( OFFSET + RANGE_AND_DIGEST[1] ))"
    > +DIGEST="${RANGE_AND_DIGEST[2]}"
    > +
    > +# The signature hash algorithm is used by Linux to blacklist certificates.
    > +# Cf. crypto/asymmetric_keys/x509_cert_parser.c:x509_note_pkey_algo()
    > +DIGEST_MATCH=""
    > +while read -r DIGEST_ITEM; do
    > + if [ -z "${DIGEST_ITEM}" ]; then
    > + break
    > + fi
    > + if echo "${DIGEST}" | grep -qiF "${DIGEST_ITEM}"; then
    > + DIGEST_MATCH="${DIGEST_ITEM}"
    > + break
    > + fi
    > +done < <(openssl list -digest-commands | tr ' ' '\n' | sort -ur)
    > +
    > +if [ -z "${DIGEST_MATCH}" ]; then
    > + echo "ERROR: Unknown digest algorithm: ${DIGEST}" >&2
    > + exit 1
    > +fi
    > +
    > +echo "${PEM}" | \
    > + openssl x509 -in - -outform DER | \
    > + dd "bs=1" "skip=${OFFSET}" "count=${END}" "status=none" | \
    > + openssl dgst "-${DIGEST_MATCH}" - | \
    > + awk '{printf "tbs:" $2}'
    > --
    > 2.30.2
    >

    \
     
     \ /
      Last update: 2021-03-15 18:10    [W:3.321 / U:0.016 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site