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

[Dmitry Kasatkin <d.kasatkin@samsung.com>]

On 09/06/14 16:48, Mimi Zohar wrote:
> On Mon, 2014-06-09 at 16:13 +0300, Dmitry Kasatkin wrote: 
>> On 07/06/14 00:50, Dmitry Kasatkin wrote:
>>> 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);

I suspect that key_put(key) is missing here...



>>>> +       }
>>>> +       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;
>> Actually this can be like this
>>
>>>> +       } else if (!prep->trusted)
>>>> +               ret = x509_validate_trust(cert,
>> get_system_trusted_keyring());
>>>> +               if (!ret)
>>>> +                       prep->trusted = 1;
>>>>         }
> Fine
>
> Mimi
>
>>>>         /* 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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