Re: [PATCH 01/20] KEYS: verify a certificate is signed by a 'trusted' key

[Dmitry Kasatkin]

On 24 April 2014 19:53, Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> wrote:
> On Wed, 2014-04-23 at 16:30 +0300, Dmitry Kasatkin wrote:
>> From: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
>>
>> 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.
>>
>> Changes:
>> - Flaged out the code to prevent build break if system keyring
>>   is not enabled (Dmitry).
>
> An updated version of this patch was posted, which resolves the Kconfig
> issues.  There are a number of other issues which need to be addressed,
> before this patch can be upstreamed.  Please refer to the patch
> description for more details -
> http://marc.info/?l=linux-security-module&m=138672063109662&w=2
>

Oh. I was using this patch from your public tree..
Updated version is missing there and I missed it out.
Will rebase on the top of it as soon as it is available.


> Reminder, as per Documentation/SubmittingPatches: "#ifdefs are ugly",
> please no ifdefs in C code.
>

Right, we know it.

Making separate C file for one function isn't ugly?

- Dmitry

> thanks,
>
> Mimi
>
>>
>> Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
>> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
>> Signed-off-by: Dmitry Kasatkin <d.kasatkin@xxxxxxxxxxx>
>> ---
>>  crypto/asymmetric_keys/x509_public_key.c | 85 +++++++++++++++++++++++++++++++-
>>  1 file changed, 84 insertions(+), 1 deletion(-)
>>
>> diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
>> index 382ef0d..d279f43 100644
>> --- a/crypto/asymmetric_keys/x509_public_key.c
>> +++ b/crypto/asymmetric_keys/x509_public_key.c
>> @@ -18,6 +18,7 @@
>>  #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"
>> @@ -102,6 +103,82 @@ int x509_check_signature(const struct public_key *pub,
>>  }
>>  EXPORT_SYMBOL_GPL(x509_check_signature);
>>
>> +#ifdef CONFIG_SYSTEM_TRUSTED_KEYRING
>> +/*
>> + * 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);
>> +}
>> +
>> +/*
>> + * 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;
>> +
>> +     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;
>> +}
>> +#endif
>> +
>>  /*
>>   * Attempt to parse a data blob for a key as an X509 certificate.
>>   */
>> @@ -155,9 +232,15 @@ 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 {
>> +#ifdef CONFIG_SYSTEM_TRUSTED_KEYRING
>> +             ret = x509_validate_trust(cert, system_trusted_keyring);
>> +             if (!ret)
>> +                     prep->trusted = 1;
>> +#endif
>>       }
>>
>>       /* Propose a description */
>
>
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-- 
Thanks,
Dmitry
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