[PATCH v5 16/18] ima: Add functions to read and verify a modsig signature

Thiago Jung Bauermann
2017-10-18T00:56:19Z

This is the code needed by IMA-appraise to work with modsig signatures.
It will be used by the next patch.

Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
---
security/integrity/ima/Kconfig | 3 +
security/integrity/ima/ima.h | 34 +++++++++++
security/integrity/ima/ima_modsig.c | 119 ++++++++++++++++++++++++++++++++++++
security/integrity/integrity.h | 1 +
4 files changed, 157 insertions(+)

diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 40c6618d00e6..55f734a6124b 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -166,6 +166,9 @@ config IMA_APPRAISE_BOOTPARAM
config IMA_APPRAISE_MODSIG
bool "Support module-style signatures for appraisal"
depends on IMA_APPRAISE
+ depends on INTEGRITY_ASYMMETRIC_KEYS
+ select PKCS7_MESSAGE_PARSER
+ select MODULE_SIG_FORMAT
default n
help
Adds support for signatures appended to files. The format of the
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 156ba218e0b6..eb58af06566f 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -257,6 +257,14 @@ int ima_read_xattr(struct dentry *dentry,

#ifdef CONFIG_IMA_APPRAISE_MODSIG
bool ima_hook_supports_modsig(enum ima_hooks func);
+int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
+ struct evm_ima_xattr_data **xattr_value,
+ int *xattr_len);
+int ima_get_modsig_hash(struct evm_ima_xattr_data *hdr, enum hash_algo *algo,
+ void const **hash, u8 *len);
+int ima_modsig_verify(const unsigned int keyring_id,
+ struct evm_ima_xattr_data *hdr);
+void ima_free_xattr_data(struct evm_ima_xattr_data *hdr);
#endif

#else
@@ -307,6 +315,32 @@ static inline bool ima_hook_supports_modsig(enum ima_hooks func)
{
return false;
}
+
+static inline int ima_read_modsig(enum ima_hooks func, const void *buf,
+ loff_t buf_len,
+ struct evm_ima_xattr_data **xattr_value,
+ int *xattr_len)
+{
+ return -ENOTSUPP;
+}
+
+static inline int ima_get_modsig_hash(struct evm_ima_xattr_data *hdr,
+ enum hash_algo *algo, void const **hash,
+ u8 *len)
+{
+ return -ENOTSUPP;
+}
+
+static inline int ima_modsig_verify(const unsigned int keyring_id,
+ struct evm_ima_xattr_data *hdr)
+{
+ return -ENOTSUPP;
+}
+
+static inline void ima_free_xattr_data(struct evm_ima_xattr_data *hdr)
+{
+ kfree(hdr);
+}
#endif

/* LSM based policy rules require audit */
diff --git a/security/integrity/ima/ima_modsig.c b/security/integrity/ima/ima_modsig.c
index 452ce6048a7e..2786aa97060e 100644
--- a/security/integrity/ima/ima_modsig.c
+++ b/security/integrity/ima/ima_modsig.c
@@ -16,8 +16,19 @@
* GNU General Public License for more details.
*/

+#include <linux/types.h>
+#include <linux/module_signature.h>
+#include <crypto/pkcs7.h>
+
#include "ima.h"

+struct modsig_hdr {
+ uint8_t type; /* Should be IMA_MODSIG. */
+ const void *data; /* Pointer to data covered by pkcs7_msg. */
+ size_t data_len;
+ struct pkcs7_message *pkcs7_msg;
+};
+
/**
* ima_hook_supports_modsig - can the policy allow modsig for this hook?
*
@@ -37,3 +48,111 @@ bool ima_hook_supports_modsig(enum ima_hooks func)
return false;
}
}
+
+int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
+ struct evm_ima_xattr_data **xattr_value,
+ int *xattr_len)
+{
+ const size_t marker_len = sizeof(MODULE_SIG_STRING) - 1;
+ const struct module_signature *sig;
+ struct modsig_hdr *hdr;
+ size_t sig_len;
+ const void *p;
+ int rc;
+
+ /*
+ * Not supposed to happen. Hooks that support modsig are
+ * whitelisted when parsing the policy using
+ * ima_hooks_supports_modsig.
+ */
+ if (!buf || !buf_len) {
+ WARN_ONCE(true, "%s doesn't support modsig\n",
+ func_tokens[func]);
+ return -ENOENT;
+ } else if (buf_len <= marker_len + sizeof(*sig))
+ return -ENOENT;
+
+ p = buf + buf_len - marker_len;
+ if (memcmp(p, MODULE_SIG_STRING, marker_len))
+ return -ENOENT;
+
+ buf_len -= marker_len;
+ sig = (const struct module_signature *) (p - sizeof(*sig));
+
+ rc = validate_module_sig(sig, buf_len);
+ if (rc)
+ return rc;
+
+ sig_len = be32_to_cpu(sig->sig_len);
+ buf_len -= sig_len + sizeof(*sig);
+
+ hdr = kmalloc(sizeof(*hdr), GFP_KERNEL);
+ if (!hdr)
+ return -ENOMEM;
+
+ hdr->pkcs7_msg = pkcs7_parse_message(buf + buf_len, sig_len);
+ if (IS_ERR(hdr->pkcs7_msg)) {
+ rc = PTR_ERR(hdr->pkcs7_msg);
+ kfree(hdr);
+ return rc;
+ }
+
+ hdr->type = IMA_MODSIG;
+ hdr->data = buf;
+ hdr->data_len = buf_len;
+
+ *xattr_value = (typeof(*xattr_value)) hdr;
+ *xattr_len = sizeof(*hdr);
+
+ return 0;
+}
+
+int ima_get_modsig_hash(struct evm_ima_xattr_data *hdr, enum hash_algo *algo,
+ void const **hash, u8 *len)
+{
+ const struct public_key_signature *pks;
+ struct modsig_hdr *modsig = (typeof(modsig)) hdr;
+ int i;
+
+ pks = pkcs7_get_message_sig(modsig->pkcs7_msg);
+ if (!pks)
+ return -EBADMSG;
+
+ for (i = 0; i < HASH_ALGO__LAST; i++)
+ if (!strcmp(hash_algo_name[i], pks->hash_algo))
+ break;
+
+ *algo = i;
+ *hash = pks->digest;
+ *len = pks->digest_size;
+
+ return 0;
+}
+
+int ima_modsig_verify(const unsigned int keyring_id,
+ struct evm_ima_xattr_data *hdr)
+{
+ struct modsig_hdr *modsig = (struct modsig_hdr *) hdr;
+ struct key *trusted_keys = integrity_keyring_from_id(keyring_id);
+
+ if (IS_ERR(trusted_keys))
+ return -EINVAL;
+
+ return verify_pkcs7_message_sig(modsig->data, modsig->data_len,
+ modsig->pkcs7_msg, trusted_keys,
+ VERIFYING_MODULE_SIGNATURE, NULL, NULL);
+}
+
+void ima_free_xattr_data(struct evm_ima_xattr_data *hdr)
+{
+ if (!hdr)
+ return;
+
+ if (hdr->type == IMA_MODSIG) {
+ struct modsig_hdr *modsig = (struct modsig_hdr *) hdr;
+
+ pkcs7_free_message(modsig->pkcs7_msg);
+ }
+
+ kfree(hdr);
+}
diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index da709558ec8b..ce2bd9d5afa5 100644
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -59,6 +59,7 @@ enum evm_ima_xattr_type {
EVM_XATTR_HMAC,
EVM_IMA_XATTR_DIGSIG,
IMA_XATTR_DIGEST_NG,
+ IMA_MODSIG,
IMA_XATTR_LAST
};