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Date: Wed, 23 Jan 2013 11:03:39 +0200
From: "Kasatkin, Dmitry" <dmitry.kasatkin@...el.com>
To: Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc: dhowells@...hat.com, jmorris@...ei.org,
linux-security-module@...r.kernel.org,
linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 1/1] ima: digital signature verification using asymmetric keys
On Wed, Jan 23, 2013 at 12:53 AM, Mimi Zohar <zohar@...ux.vnet.ibm.com> wrote:
> 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.kasatkin@...el.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?
>
Will do it.
- Dmitry
> thanks,
>
> Mimi
>
>
>
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