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@xxxxxxxxx>
---
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);
}
--
1.7.10.4
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