certs: Allow root user to append signed hashes to the blacklist keyring
Add a kernel option SYSTEM_BLACKLIST_AUTH_UPDATE to enable the root user to dynamically add new keys to the blacklist keyring. This enables to invalidate new certificates, either from being loaded in a keyring, or from being trusted in a PKCS#7 certificate chain. This also enables to add new file hashes to be denied by the integrity infrastructure. Being able to untrust a certificate which could have normaly been trusted is a sensitive operation. This is why adding new hashes to the blacklist keyring is only allowed when these hashes are signed and vouched by the builtin trusted keyring. A blacklist hash is stored as a key description. The PKCS#7 signature of this description must be provided as the key payload. Marking a certificate as untrusted should be enforced while the system is running. It is then forbiden to remove such blacklist keys. Update blacklist keyring, blacklist key and revoked certificate access rights: * allows the root user to search for a specific blacklisted hash, which make sense because the descriptions are already viewable; * forbids key update (blacklist and asymmetric ones); * restricts kernel rights on the blacklist keyring to align with the root user rights. See help in tools/certs/print-cert-tbs-hash.sh . Cc: David Howells <dhowells@redhat.com> Cc: David Woodhouse <dwmw2@infradead.org> Cc: Eric Snowberg <eric.snowberg@oracle.com> Cc: Jarkko Sakkinen <jarkko@kernel.org> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com> Link: https://lore.kernel.org/r/20210712170313.884724-6-mic@digikod.net Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org> Tested-by: Jarkko Sakkinen <jarkko@kernel.org> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
This commit is contained in:
Mickaël Salaün
Jarkko Sakkinen
parent
addf466389
commit
6364d106e0
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@ -127,4 +127,14 @@ config SYSTEM_REVOCATION_KEYS
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containing X.509 certificates to be included in the default blacklist
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keyring.
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config SYSTEM_BLACKLIST_AUTH_UPDATE
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bool "Allow root to add signed blacklist keys"
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depends on SYSTEM_BLACKLIST_KEYRING
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depends on SYSTEM_DATA_VERIFICATION
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help
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If set, provide the ability to load new blacklist keys at run time if
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they are signed and vouched by a certificate from the builtin trusted
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keyring. The PKCS#7 signature of the description is set in the key
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payload. Blacklist keys cannot be removed.
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endmenu
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@ -15,6 +15,7 @@
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#include <linux/err.h>
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#include <linux/seq_file.h>
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#include <linux/uidgid.h>
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#include <linux/verification.h>
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#include <keys/system_keyring.h>
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#include "blacklist.h"
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#include "common.h"
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@ -26,6 +27,9 @@
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*/
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#define MAX_HASH_LEN 128
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#define BLACKLIST_KEY_PERM (KEY_POS_SEARCH | KEY_POS_VIEW | \
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KEY_USR_SEARCH | KEY_USR_VIEW)
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static const char tbs_prefix[] = "tbs";
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static const char bin_prefix[] = "bin";
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@ -80,19 +84,51 @@ found_colon:
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return 0;
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}
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/*
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* The hash to be blacklisted is expected to be in the description. There will
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* be no payload.
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*/
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static int blacklist_preparse(struct key_preparsed_payload *prep)
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static int blacklist_key_instantiate(struct key *key,
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struct key_preparsed_payload *prep)
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{
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if (prep->datalen > 0)
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return -EINVAL;
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return 0;
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#ifdef CONFIG_SYSTEM_BLACKLIST_AUTH_UPDATE
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int err;
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#endif
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/* Sets safe default permissions for keys loaded by user space. */
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key->perm = BLACKLIST_KEY_PERM;
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/*
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* Skips the authentication step for builtin hashes, they are not
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* signed but still trusted.
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*/
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if (key->flags & (1 << KEY_FLAG_BUILTIN))
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goto out;
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#ifdef CONFIG_SYSTEM_BLACKLIST_AUTH_UPDATE
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/*
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* Verifies the description's PKCS#7 signature against the builtin
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* trusted keyring.
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*/
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err = verify_pkcs7_signature(key->description,
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strlen(key->description), prep->data, prep->datalen,
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NULL, VERIFYING_UNSPECIFIED_SIGNATURE, NULL, NULL);
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if (err)
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return err;
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#else
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/*
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* It should not be possible to come here because the keyring doesn't
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* have KEY_USR_WRITE and the only other way to call this function is
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* for builtin hashes.
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*/
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WARN_ON_ONCE(1);
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return -EPERM;
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#endif
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out:
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return generic_key_instantiate(key, prep);
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}
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static void blacklist_free_preparse(struct key_preparsed_payload *prep)
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static int blacklist_key_update(struct key *key,
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struct key_preparsed_payload *prep)
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{
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return -EPERM;
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}
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static void blacklist_describe(const struct key *key, struct seq_file *m)
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@ -103,9 +139,8 @@ static void blacklist_describe(const struct key *key, struct seq_file *m)
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static struct key_type key_type_blacklist = {
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.name = "blacklist",
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.vet_description = blacklist_vet_description,
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.preparse = blacklist_preparse,
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.free_preparse = blacklist_free_preparse,
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.instantiate = generic_key_instantiate,
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.instantiate = blacklist_key_instantiate,
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.update = blacklist_key_update,
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.describe = blacklist_describe,
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};
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@ -154,8 +189,7 @@ static int mark_raw_hash_blacklisted(const char *hash)
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hash,
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NULL,
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0,
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((KEY_POS_ALL & ~KEY_POS_SETATTR) |
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KEY_USR_VIEW),
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BLACKLIST_KEY_PERM,
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KEY_ALLOC_NOT_IN_QUOTA |
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KEY_ALLOC_BUILT_IN);
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if (IS_ERR(key)) {
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@ -232,8 +266,10 @@ int add_key_to_revocation_list(const char *data, size_t size)
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NULL,
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data,
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size,
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((KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_VIEW),
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KEY_ALLOC_NOT_IN_QUOTA | KEY_ALLOC_BUILT_IN);
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KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH
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| KEY_USR_VIEW,
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KEY_ALLOC_NOT_IN_QUOTA | KEY_ALLOC_BUILT_IN
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| KEY_ALLOC_BYPASS_RESTRICTION);
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if (IS_ERR(key)) {
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pr_err("Problem with revocation key (%ld)\n", PTR_ERR(key));
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@ -260,25 +296,43 @@ int is_key_on_revocation_list(struct pkcs7_message *pkcs7)
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}
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#endif
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static int restrict_link_for_blacklist(struct key *dest_keyring,
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const struct key_type *type, const union key_payload *payload,
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struct key *restrict_key)
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{
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if (type == &key_type_blacklist)
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return 0;
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return -EOPNOTSUPP;
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}
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/*
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* Initialise the blacklist
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*/
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static int __init blacklist_init(void)
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{
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const char *const *bl;
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struct key_restriction *restriction;
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if (register_key_type(&key_type_blacklist) < 0)
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panic("Can't allocate system blacklist key type\n");
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restriction = kzalloc(sizeof(*restriction), GFP_KERNEL);
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if (!restriction)
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panic("Can't allocate blacklist keyring restriction\n");
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restriction->check = restrict_link_for_blacklist;
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blacklist_keyring =
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keyring_alloc(".blacklist",
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GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(),
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(KEY_POS_ALL & ~KEY_POS_SETATTR) |
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KEY_USR_VIEW | KEY_USR_READ |
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KEY_USR_SEARCH,
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KEY_ALLOC_NOT_IN_QUOTA |
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KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH |
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KEY_POS_WRITE |
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KEY_USR_VIEW | KEY_USR_READ | KEY_USR_SEARCH
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#ifdef CONFIG_SYSTEM_BLACKLIST_AUTH_UPDATE
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| KEY_USR_WRITE
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#endif
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, KEY_ALLOC_NOT_IN_QUOTA |
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KEY_ALLOC_SET_KEEP,
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NULL, NULL);
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restriction, NULL);
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if (IS_ERR(blacklist_keyring))
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panic("Can't allocate system blacklist keyring\n");
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