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

Dmitry Kasatkin
2014-06-09T14:58:23Z

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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>>>
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