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Date: Tue, 22 Jan 2013 17:53:48 -0500
From: Mimi Zohar <zohar@...ux.vnet.ibm.com>
To: Dmitry Kasatkin <dmitry.kasatkin@...el.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 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?
thanks,
Mimi
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