On Tue, 2013-01-15 at 12:34 +0200, Dmitry Kasatkin wrote:
> Asymmetric keys were introduced in linux-3.7 to verify the signature on
> signed kernel modules.  The asymmetric keys infrastructure abstracts the
> signature verification from the crypto details.  This patch adds IMA/EVM
> signature verification using asymmetric keys.  Support for additional
> signature verification methods can now be delegated to the asymmetric
> key infrastructure.
> 
> Signed-off-by: Dmitry Kasatkin <dmitry.kasat...@intel.com>
> ---
>  security/integrity/Kconfig  |   12 +++++
>  security/integrity/digsig.c |  103 
> ++++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 114 insertions(+), 1 deletion(-)
> 
> diff --git a/security/integrity/Kconfig b/security/integrity/Kconfig
> index 5bd1cc1..19c4187 100644
> --- a/security/integrity/Kconfig
> +++ b/security/integrity/Kconfig
> @@ -17,5 +17,17 @@ config INTEGRITY_SIGNATURE
>         This is useful for evm and module keyrings, when keys are
>         usually only added from initramfs.
> 
> +config INTEGRITY_ASYMMETRIC_KEYS
> +     boolean "Digital signature verification using asymmetric keys"
> +     depends on INTEGRITY_SIGNATURE
> +     default n
> +        select ASYMMETRIC_KEY_TYPE
> +        select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
> +        select PUBLIC_KEY_ALGO_RSA
> +        select X509_CERTIFICATE_PARSER
> +     help
> +       This option enables digital signature verification support
> +       using asymmetric keys.
> +
>  source security/integrity/ima/Kconfig
>  source security/integrity/evm/Kconfig
> diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
> index 2dc167d..1896537 100644
> --- a/security/integrity/digsig.c
> +++ b/security/integrity/digsig.c
> @@ -15,10 +15,22 @@
>  #include <linux/err.h>
>  #include <linux/rbtree.h>
>  #include <linux/key-type.h>
> +#include <crypto/public_key.h>
> +#include <keys/asymmetric-type.h>
>  #include <linux/digsig.h>
> 
>  #include "integrity.h"
> 
> +/*
> + * signature format v2 - for using with asymmetric keys
> + */
> +struct signature_v2_hdr {
> +     uint8_t version;        /* signature format version */
> +     uint8_t hash_algo;      /* Digest algorithm [enum pkey_hash_algo] */
> +     uint8_t keyid[8];       /* IMA key identifier - not X509/PGP specific*/
> +     uint8_t payload[0];     /* signature payload */
> +} __packed;
> +
>  static struct key *keyring[INTEGRITY_KEYRING_MAX];
> 
>  static const char *keyring_name[INTEGRITY_KEYRING_MAX] = {
> @@ -27,6 +39,91 @@ static const char *keyring_name[INTEGRITY_KEYRING_MAX] = {
>       "_ima",
>  };
> 
> +#ifdef CONFIG_INTEGRITY_ASYMMETRIC_KEYS
> +
> +/*
> + * Request an asymmetric key.
> + */
> +static struct key *request_asymmetric_key(struct key *keyring, uint8_t 
> *keyid)
> +{
> +     struct key *key;
> +     char name[20];
> +
> +     sprintf(name, "%llX", __be64_to_cpup((uint64_t *)keyid));
> +
> +     pr_debug("key search: \"%s\"\n", name);
> +
> +     if (keyring) {
> +             /* search in specific keyring */
> +             key_ref_t kref;
> +             kref = keyring_search(make_key_ref(keyring, 1),
> +                                   &key_type_asymmetric, name);
> +             if (IS_ERR(kref))
> +                     key = ERR_CAST(kref);
> +             else
> +                     key = key_ref_to_ptr(kref);
> +     } else {
> +             key = request_key(&key_type_asymmetric, name, NULL);
> +     }
> +
> +     if (IS_ERR(key)) {
> +             pr_warn("Request for unknown key '%s' err %ld\n",
> +                     name, PTR_ERR(key));
> +             switch (PTR_ERR(key)) {
> +                     /* Hide some search errors */
> +             case -EACCES:
> +             case -ENOTDIR:
> +             case -EAGAIN:
> +                     return ERR_PTR(-ENOKEY);
> +             default:
> +                     return key;
> +             }
> +     }
> +
> +     pr_debug("%s() = 0 [%x]\n", __func__, key_serial(key));
> +
> +     return key;
> +}
> +
> +static int asymmetric_verify(struct key *keyring, const char *sig,
> +                          size_t siglen, const char *data, int datalen)
> +{
> +     struct public_key_signature pks;
> +     struct signature_v2_hdr *hdr = (struct signature_v2_hdr *)sig;
> +     struct key *key;
> +     int ret = -ENOMEM;
> +
> +     if (siglen <= sizeof(*hdr))
> +             return -EBADMSG;
> +
> +     siglen -= sizeof(*hdr);
> +
> +     if (hdr->hash_algo >= PKEY_HASH__LAST)
> +             return -ENOPKG;
> +
> +     key = request_asymmetric_key(keyring, hdr->keyid);
> +     if (IS_ERR(key))
> +             return PTR_ERR(key);
> +
> +     memset(&pks, 0, sizeof(pks));
> +
> +     pks.pkey_hash_algo = hdr->hash_algo;
> +     pks.digest = (u8 *)data;
> +     pks.digest_size = datalen;
> +     pks.nr_mpi = 1;
> +     pks.rsa.s = mpi_read_from_buffer(hdr->payload, &siglen);
> +
> +     if (pks.rsa.s)
> +             ret = verify_signature(key, &pks);
> +
> +     mpi_free(pks.rsa.s);
> +     key_put(key);
> +     pr_debug("%s() = %d\n", __func__, ret);
> +     return ret;
> +}
> +
> +#endif /* CONFIG_INTEGRITY_ASYMMETRIC_KEYS */
> +
>  int integrity_digsig_verify(const unsigned int id, const char *sig, int 
> siglen,
>                                       const char *digest, int digestlen)
>  {
> @@ -43,6 +140,10 @@ int integrity_digsig_verify(const unsigned int id, const 
> char *sig, int siglen,
>                       return err;
>               }
>       }
> -
> +#ifdef CONFIG_INTEGRITY_ASYMMETRIC_KEYS
> +     if (sig[0] == 2)
> +             return asymmetric_verify(keyring[id], sig, siglen,
> +                                      digest, digestlen);
> +#endif
>       return digsig_verify(keyring[id], sig, siglen, digest, digestlen);
>  }

Thanks Dmitry for the patch!  According to
Documentation/SubmittingPatches: section 2.2, #ifdefs are ugly.  I
realize this is a really small '.c' file, and doesn't really hurt
readability, but could you remove the ifdefs anyway?

thanks,

Mimi



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