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Fri, 6 Nov 2026 17:31:55 +0000 (GMT) Received: from li-43857255-d5e6-4659-90f1-fc5cee4750ad.ibm.com.com (unknown [9.61.47.32]) by smtpav04.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 6 Nov 2026 17:31:55 +0000 (GMT) From: Mimi Zohar To: linux-integrity@vger.kernel.org Cc: Mimi Zohar , Jarkko Sakkinen , David Howells , Roberto Sassu , =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= , keyrings@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 1/3] certs: blacklist: define skid: entries and add is_key_blacklisted() Date: Fri, 6 Nov 2026 12:31:47 -0500 Message-ID: <20261106173149.707244-2-zohar@linux.ibm.com> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261106173149.707244-1-zohar@linux.ibm.com> References: <20261106173149.707244-1-zohar@linux.ibm.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: _av4UAfr_JQG5LfvNCPTAKqq8RrLxJB7 X-Proofpoint-GUID: _av4UAfr_JQG5LfvNCPTAKqq8RrLxJB7 X-Authority-Analysis: v=2.4 cv=MqLHeGae c=1 sm=1 tr=0 ts=6aee0f10 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=zJRp6_cAMcgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VnNF1IyMAAAA:8 a=VWuc2nmrMmYy7wgmrS0A:9 X-Proofpoint-Spam-Info: AW1haW4tMjYxMTA2MDA2OCBTYWx0ZWRfX0CDbhBcG8/Qx Ql2kOzK8xgZgtObyHPR59Jeyf6KCpjWA3nylaG9hwiRSikcuGdOCreu9in6qq6vLdgqUVyp5d7n fDYvM7OGn6wXWYXYS7TavKo9bb50ChU= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMTA2MDA2OCBTYWx0ZWRfX7i7aCxB4hYLp +YQW0Ix1TMs8bchAnxiLYMSAjoDPqNiZLVdN0KZVVi6R4pYJW+xzbhaSC6qAwi2S79RS+5K6DKZ J9IEK8J/VcMav55c4g+SXLaY0wNvgVik1/FdGgtrAfAkjfaepja9Y2rPS3z4FwbzVrvj0zzbwtN 9LWY2PH5crYksfHMsJzBo8mF7fDD2WB4L99PXhwYk+BLOdRgkf9KRpPnt/StH4uVLl56SBWMfro tpAuhhW2B1W7rlBzih8n30i0g8W8B2jJ1DsJ3WxAJCzewDgUr0/0lm4vH6n7ABNlr3eouAdTIOB Pm38Q5HPskq34Qn+R1Y2hfyAHxKyolzW8LBaqfelhRYh6biTNO0uEzf7T7NSqjCqTeZYPHruF4V b4cXtsL0TTbkj1SIh+4vNeFvNOgQOqlxSknTZWHXKjAgoZgSXUpXDGg+W8UKG6p+o8NVeAYcnS7 jkO3sorNyMCDOW1H33Q== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.138,FMLib:17.12.100.49 definitions=2026-11-06_05,2026-11-06_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 phishscore=0 priorityscore=1501 adultscore=0 clxscore=1015 malwarescore=0 impostorscore=0 spamscore=0 lowpriorityscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2611040001 definitions=main-2611060068 A "tbs:" blacklist entry is only compared against certificates being added to a keyring or presented in a signature chain, so it does not stop a key that is already loaded from being used as a trust anchor. Define a new "skid:" blacklist entry, holding a Subject Key Identifier, and add is_key_blacklisted(), which looks up the SKID of an asymmetric key in the system blacklist. Entries are added like "tbs:" and "bin:" entries and are subject to CONFIG_SYSTEM_BLACKLIST_AUTH_UPDATE. blacklist_vet_description() now uses a prefix table, since the prefixes no longer all have the same length. "tbs:" and "bin:" entries behave as before. For example, to add an entry for a certificate (the signed string must not include a trailing newline): skid=$(openssl x509 -in cert.pem -noout -ext subjectKeyIdentifier | sed -n '2s/[ :]//gp' | tr A-F a-f) printf 'skid:%s' "$skid" > skid.txt openssl smime -sign -binary -noattr -in skid.txt -signer signer.crt \ -inkey signer.key -outform DER -out skid.p7s keyctl padd blacklist "skid:$skid" %:.blacklist < skid.p7s The SKID is also the hex string in the description of the key on a keyring, and its last four bytes are the key ID in the security.ima xattr, so an entry is easy to correlate with the key it revokes: # keyctl show %:.ima | grep 073d 927946571 --als--v 0 0 \_ asymmetric: test signing key: b7809c3372a07fe87248dcec7ff047a40fb3073d # keyctl show %:.blacklist | grep skid 1014808518 ----s--v 0 0 \_ blacklist: skid:b7809c3372a07fe87248dcec7ff047a40fb3073d Signed-off-by: Mimi Zohar --- Changelog v1: - Addressed Sashiko issues: drop Kconfig change, linking issues when blacklist support configured, but without CONFIG_ASYMMETRIC_KEY_TYPE configured. certs/blacklist.c | 83 ++++++++++++++++++++++++----------- include/keys/system_keyring.h | 12 +++++ 2 files changed, 70 insertions(+), 25 deletions(-) diff --git a/certs/blacklist.c b/certs/blacklist.c index fa561c12eabf..9158bd9f9fc9 100644 --- a/certs/blacklist.c +++ b/certs/blacklist.c @@ -32,6 +32,7 @@ static const char tbs_prefix[] = "tbs"; static const char bin_prefix[] = "bin"; +static const char skid_prefix[] = "skid"; static struct key *blacklist_keyring; @@ -40,36 +41,30 @@ extern __initconst const u8 revocation_certificate_list[]; extern __initconst const unsigned long revocation_certificate_list_size; #endif +static bool blacklist_prefix_valid(const char *desc, size_t len) +{ + return (len == sizeof(tbs_prefix) - 1 && + !strncmp(desc, tbs_prefix, len)) || + (len == sizeof(bin_prefix) - 1 && + !strncmp(desc, bin_prefix, len)) || + (len == sizeof(skid_prefix) - 1 && + !strncmp(desc, skid_prefix, len)); +} + /* - * The description must be a type prefix, a colon and then an even number of - * hex digits. The hash is kept in the description. + * The description must be a type prefix ("tbs", "bin" or "skid"), a colon and + * then an even number of lower-case hex digits. The hash (or, for "skid", the + * Subject Key Identifier) is kept in the description. */ static int blacklist_vet_description(const char *desc) { - int i, prefix_len, tbs_step = 0, bin_step = 0; - - /* The following algorithm only works if prefix lengths match. */ - BUILD_BUG_ON(sizeof(tbs_prefix) != sizeof(bin_prefix)); - prefix_len = sizeof(tbs_prefix) - 1; - for (i = 0; *desc; desc++, i++) { - if (*desc == ':') { - if (tbs_step == prefix_len) - goto found_colon; - if (bin_step == prefix_len) - goto found_colon; - return -EINVAL; - } - if (i >= prefix_len) - return -EINVAL; - if (*desc == tbs_prefix[i]) - tbs_step++; - if (*desc == bin_prefix[i]) - bin_step++; - } - return -EINVAL; + const char *colon = strchr(desc, ':'); + int i; -found_colon: - desc++; + if (!colon || !blacklist_prefix_valid(desc, colon - desc)) + return -EINVAL; + + desc = colon + 1; for (i = 0; *desc && i < MAX_HASH_LEN; desc++, i++) { if (!isxdigit(*desc) || isupper(*desc)) return -EINVAL; @@ -160,6 +155,10 @@ static char *get_raw_hash(const u8 *hash, size_t hash_len, type_len = sizeof(bin_prefix) - 1; type_prefix = bin_prefix; break; + case BLACKLIST_HASH_SKID: + type_len = sizeof(skid_prefix) - 1; + type_prefix = skid_prefix; + break; default: WARN_ON_ONCE(1); return ERR_PTR(-EINVAL); @@ -244,6 +243,40 @@ int is_hash_blacklisted(const u8 *hash, size_t hash_len, } EXPORT_SYMBOL_GPL(is_hash_blacklisted); +#ifdef CONFIG_ASYMMETRIC_KEY_TYPE +/** + * is_key_blacklisted - Determine if a key is blacklisted by its SKID + * @key: The key to be checked, e.g. a trust anchor found in a keyring + * + * Unlike a "tbs:" entry, which is only compared against certificates being + * added or presented in a chain, this checks a key that is already loaded, so + * that keys that cannot be unlinked from their keyring can still be revoked. + * The identifier is taken from the key itself, not from the caller. + * + * Returns -EKEYREJECTED if the key's Subject Key Identifier is blacklisted, + * 0 if it is not (or the key has no SKID), or another negative error. + */ +int is_key_blacklisted(const struct key *key) +{ + const struct asymmetric_key_ids *kids; + const struct asymmetric_key_id *skid; + + if (!key || key->type != &key_type_asymmetric) + return 0; + + kids = asymmetric_key_ids(key); + if (!kids) + return 0; + + skid = kids->id[1]; + if (!skid || !skid->len) + return 0; + + return is_hash_blacklisted(skid->data, skid->len, BLACKLIST_HASH_SKID); +} +EXPORT_SYMBOL_GPL(is_key_blacklisted); +#endif + int is_binary_blacklisted(const u8 *hash, size_t hash_len) { if (is_hash_blacklisted(hash, hash_len, BLACKLIST_HASH_BINARY) == diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h index a6c2897bcc63..2ac1dae2063a 100644 --- a/include/keys/system_keyring.h +++ b/include/keys/system_keyring.h @@ -15,6 +15,8 @@ enum blacklist_hash_type { BLACKLIST_HASH_X509_TBS = 1, /* Raw data hash */ BLACKLIST_HASH_BINARY = 2, + /* Subject Key Identifier of a key (not a hash) */ + BLACKLIST_HASH_SKID = 3, }; #ifdef CONFIG_SYSTEM_TRUSTED_KEYRING @@ -92,6 +94,16 @@ static inline int is_binary_blacklisted(const u8 *hash, size_t hash_len) } #endif +#if defined(CONFIG_SYSTEM_BLACKLIST_KEYRING) && \ + defined(CONFIG_ASYMMETRIC_KEY_TYPE) +extern int is_key_blacklisted(const struct key *key); +#else +static inline int is_key_blacklisted(const struct key *key) +{ + return 0; +} +#endif + struct pkcs7_message; #ifdef CONFIG_SYSTEM_REVOCATION_LIST extern int add_key_to_revocation_list(const char *data, size_t size); -- 2.56.0