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    Subject[PATCH v6 5/6] KEYS: CA link restriction
    Date
    Add a new link restriction.  Restrict the addition of keys in a keyring
    based on the key to be added being a CA.

    Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
    Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
    ---
    crypto/asymmetric_keys/restrict.c | 42 +++++++++++++++++++++++++++++++
    include/crypto/public_key.h | 15 +++++++++++
    2 files changed, 57 insertions(+)

    diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
    index 6b1ac5f5896a..dd9ced32c8a1 100644
    --- a/crypto/asymmetric_keys/restrict.c
    +++ b/crypto/asymmetric_keys/restrict.c
    @@ -108,6 +108,48 @@ int restrict_link_by_signature(struct key *dest_keyring,
    return ret;
    }

    +/**
    + * restrict_link_by_ca - Restrict additions to a ring of CA keys
    + * @dest_keyring: Keyring being linked to.
    + * @type: The type of key being added.
    + * @payload: The payload of the new key.
    + * @trust_keyring: Unused.
    + *
    + * Check if the new certificate is a CA. If it is a CA, then mark the new
    + * certificate as being ok to link.
    + *
    + * Returns 0 if the new certificate was accepted, -ENOKEY if the
    + * certificate is not a CA. -ENOPKG if the signature uses unsupported
    + * crypto, or some other error if there is a matching certificate but
    + * the signature check cannot be performed.
    + */
    +int restrict_link_by_ca(struct key *dest_keyring,
    + const struct key_type *type,
    + const union key_payload *payload,
    + struct key *trust_keyring)
    +{
    + const struct public_key *pkey;
    +
    + if (type != &key_type_asymmetric)
    + return -EOPNOTSUPP;
    +
    + pkey = payload->data[asym_crypto];
    +
    + if (!pkey)
    + return -ENOPKG;
    +
    + if (!test_bit(KEY_EFLAG_CA, &pkey->key_eflags))
    + return -ENOKEY;
    +
    + if (!test_bit(KEY_EFLAG_KEYCERTSIGN, &pkey->key_eflags))
    + return -ENOKEY;
    +
    + if (test_bit(KEY_EFLAG_DIGITALSIG, &pkey->key_eflags))
    + return -ENOKEY;
    +
    + return 0;
    +}
    +
    static bool match_either_id(const struct asymmetric_key_id **pair,
    const struct asymmetric_key_id *single)
    {
    diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
    index 03c3fb990d59..653992a6e941 100644
    --- a/include/crypto/public_key.h
    +++ b/include/crypto/public_key.h
    @@ -75,6 +75,21 @@ extern int restrict_link_by_key_or_keyring_chain(struct key *trust_keyring,
    const union key_payload *payload,
    struct key *trusted);

    +#if IS_REACHABLE(CONFIG_ASYMMETRIC_KEY_TYPE)
    +extern int restrict_link_by_ca(struct key *dest_keyring,
    + const struct key_type *type,
    + const union key_payload *payload,
    + struct key *trust_keyring);
    +#else
    +static inline int restrict_link_by_ca(struct key *dest_keyring,
    + const struct key_type *type,
    + const union key_payload *payload,
    + struct key *trust_keyring)
    +{
    + return 0;
    +}
    +#endif
    +
    extern int query_asymmetric_key(const struct kernel_pkey_params *,
    struct kernel_pkey_query *);

    --
    2.27.0
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