Re: [RFC PATCH v5 2/4] KEYS: verify a certificate is signed by a 'trusted' key

Dmitry Kasatkin
2014-06-06T21:50:09Z

On 3 June 2014 20:58, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote:
> Only public keys, with certificates signed by an existing
> 'trusted' key on the system trusted keyring, should be added
> to a trusted keyring. This patch adds support for verifying
> a certificate's signature.
>
> This is derived from David Howells pkcs7_request_asymmetric_key() patch.
>
> Changelog:
> - define get_system_trusted_keyring() to fix kbuild issues
>
> Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
> Signed-off-by: David Howells <dhowells@redhat.com>

Acked-by: me

> ---
> crypto/asymmetric_keys/x509_public_key.c | 84 +++++++++++++++++++++++++++++++-
> include/keys/system_keyring.h | 10 +++-
> 2 files changed, 92 insertions(+), 2 deletions(-)
>
> diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
> index 382ef0d..1af8a30 100644
> --- a/crypto/asymmetric_keys/x509_public_key.c
> +++ b/crypto/asymmetric_keys/x509_public_key.c
> @@ -18,12 +18,60 @@
> #include <linux/asn1_decoder.h>
> #include <keys/asymmetric-subtype.h>
> #include <keys/asymmetric-parser.h>
> +#include <keys/system_keyring.h>
> #include <crypto/hash.h>
> #include "asymmetric_keys.h"
> #include "public_key.h"
> #include "x509_parser.h"
>
> /*
> + * Find a key in the given keyring by issuer and authority.
> + */
> +static struct key *x509_request_asymmetric_key(
> + struct key *keyring,
> + const char *signer, size_t signer_len,
> + const char *authority, size_t auth_len)
> +{
> + key_ref_t key;
> + char *id;
> +
> + /* Construct an identifier. */
> + id = kmalloc(signer_len + 2 + auth_len + 1, GFP_KERNEL);
> + if (!id)
> + return ERR_PTR(-ENOMEM);
> +
> + memcpy(id, signer, signer_len);
> + id[signer_len + 0] = ':';
> + id[signer_len + 1] = ' ';
> + memcpy(id + signer_len + 2, authority, auth_len);
> + id[signer_len + 2 + auth_len] = 0;
> +
> + pr_debug("Look up: \"%s\"\n", id);
> +
> + key = keyring_search(make_key_ref(keyring, 1),
> + &key_type_asymmetric, id);
> + if (IS_ERR(key))
> + pr_debug("Request for module key '%s' err %ld\n",
> + id, PTR_ERR(key));
> + kfree(id);
> +
> + if (IS_ERR(key)) {
> + switch (PTR_ERR(key)) {
> + /* Hide some search errors */
> + case -EACCES:
> + case -ENOTDIR:
> + case -EAGAIN:
> + return ERR_PTR(-ENOKEY);
> + default:
> + return ERR_CAST(key);
> + }
> + }
> +
> + pr_devel("<==%s() = 0 [%x]\n", __func__, key_serial(key_ref_to_ptr(key)));
> + return key_ref_to_ptr(key);
> +}
> +
> +/*
> * Set up the signature parameters in an X.509 certificate. This involves
> * digesting the signed data and extracting the signature.
> */
> @@ -103,6 +151,36 @@ int x509_check_signature(const struct public_key *pub,
> EXPORT_SYMBOL_GPL(x509_check_signature);
>
> /*
> + * Check the new certificate against the ones in the trust keyring. If one of
> + * those is the signing key and validates the new certificate, then mark the
> + * new certificate as being trusted.
> + *
> + * Return 0 if the new certificate was successfully validated, 1 if we couldn't
> + * find a matching parent certificate in the trusted list and an error if there
> + * is a matching certificate but the signature check fails.
> + */
> +static int x509_validate_trust(struct x509_certificate *cert,
> + struct key *trust_keyring)
> +{
> + const struct public_key *pk;
> + struct key *key;
> + int ret = 1;
> +
> + if (!trust_keyring)
> + return -EOPNOTSUPP;
> +
> + key = x509_request_asymmetric_key(trust_keyring,
> + cert->issuer, strlen(cert->issuer),
> + cert->authority,
> + strlen(cert->authority));
> + if (!IS_ERR(key)) {
> + pk = key->payload.data;
> + ret = x509_check_signature(pk, cert);
> + }
> + return ret;
> +}
> +
> +/*
> * Attempt to parse a data blob for a key as an X509 certificate.
> */
> static int x509_key_preparse(struct key_preparsed_payload *prep)
> @@ -155,9 +233,13 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
> /* Check the signature on the key if it appears to be self-signed */
> if (!cert->authority ||
> strcmp(cert->fingerprint, cert->authority) == 0) {
> - ret = x509_check_signature(cert->pub, cert);
> + ret = x509_check_signature(cert->pub, cert); /* self-signed */
> if (ret < 0)
> goto error_free_cert;
> + } else {
> + ret = x509_validate_trust(cert, get_system_trusted_keyring());
> + if (!ret)
> + prep->trusted = 1;
> }
>
> /* Propose a description */
> diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
> index 8dabc39..72665eb 100644
> --- a/include/keys/system_keyring.h
> +++ b/include/keys/system_keyring.h
> @@ -17,7 +17,15 @@
> #include <linux/key.h>
>
> extern struct key *system_trusted_keyring;
> -
> +static inline struct key *get_system_trusted_keyring(void)
> +{
> + return system_trusted_keyring;
> +}
> +#else
> +static inline struct key *get_system_trusted_keyring(void)
> +{
> + return NULL;
> +}
> #endif
>
> #endif /* _KEYS_SYSTEM_KEYRING_H */
> --
> 1.8.1.4
>
> --
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--
Thanks,
Dmitry