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Subject[PATCH v6 10/12] ima: Add functions to read and verify a modsig signature
Date
This is the code needed by IMA-appraise to work with modsig signatures.
It will be used by the next two patches.

Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
---
security/integrity/ima/Kconfig | 3 +
security/integrity/ima/ima.h | 41 ++++++++
security/integrity/ima/ima_modsig.c | 181 ++++++++++++++++++++++++++++++++++++
security/integrity/integrity.h | 1 +
4 files changed, 226 insertions(+)

diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index ee278189e0bb..306601d62f0b 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -167,6 +167,9 @@ 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 c61d8fc5190d..49aef56dc96d 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -301,11 +301,52 @@ static inline 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,
+ const u8 **hash, u8 *len);
+int ima_modsig_serialize_data(struct evm_ima_xattr_data **data, int *data_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);
#else
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, const u8 **hash,
+ u8 *len)
+{
+ return -ENOTSUPP;
+}
+
+static inline int ima_modsig_serialize_data(struct evm_ima_xattr_data **data,
+ int *data_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 /* CONFIG_IMA_APPRAISE_MODSIG */

/* LSM based policy rules require audit */
diff --git a/security/integrity/ima/ima_modsig.c b/security/integrity/ima/ima_modsig.c
index d8ea811b6f74..105fd04d585e 100644
--- a/security/integrity/ima/ima_modsig.c
+++ b/security/integrity/ima/ima_modsig.c
@@ -8,8 +8,25 @@
* Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
*/

+#include <linux/types.h>
+#include <linux/module_signature.h>
+#include <keys/asymmetric-type.h>
+#include <crypto/pkcs7.h>
+
#include "ima.h"

+struct modsig_hdr {
+ uint8_t type; /* Should be IMA_MODSIG. */
+ struct pkcs7_message *pkcs7_msg;
+ int raw_pkcs7_len;
+
+ /*
+ * This is what will go to the measurement list if the template requires
+ * storing the signature.
+ */
+ struct evm_ima_xattr_data raw_pkcs7;
+};
+
/**
* ima_hook_supports_modsig - can the policy allow modsig for this hook?
*
@@ -29,3 +46,167 @@ bool ima_hook_supports_modsig(enum ima_hooks func)
return false;
}
}
+
+static bool modsig_has_known_key(struct modsig_hdr *hdr)
+{
+ const struct public_key_signature *pks;
+ struct key *keyring;
+ struct key *key;
+
+ keyring = integrity_keyring_from_id(INTEGRITY_KEYRING_IMA);
+ if (IS_ERR(keyring))
+ return false;
+
+ pks = pkcs7_get_message_sig(hdr->pkcs7_msg);
+ if (!pks)
+ return false;
+
+ key = find_asymmetric_key(keyring, pks->auth_ids[0], NULL, false);
+ if (IS_ERR(key))
+ return false;
+
+ key_put(key);
+
+ return true;
+}
+
+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);
+
+ /* Allocate sig_len additional bytes to hold the raw PKCS#7 data. */
+ hdr = kmalloc(sizeof(*hdr) + sig_len, 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);
+ goto err_no_msg;
+ }
+
+ rc = pkcs7_supply_detached_data(hdr->pkcs7_msg, buf, buf_len);
+ if (rc)
+ goto err;
+
+ if (!modsig_has_known_key(hdr)) {
+ rc = -ENOKEY;
+ goto err;
+ }
+
+ memcpy(hdr->raw_pkcs7.data, buf + buf_len, sig_len);
+ hdr->raw_pkcs7_len = sig_len + 1;
+ hdr->raw_pkcs7.type = IMA_MODSIG;
+
+ hdr->type = IMA_MODSIG;
+
+ *xattr_value = (typeof(*xattr_value)) hdr;
+ *xattr_len = sizeof(*hdr);
+
+ return 0;
+
+ err:
+ pkcs7_free_message(hdr->pkcs7_msg);
+ err_no_msg:
+ kfree(hdr);
+ return rc;
+}
+
+int ima_get_modsig_hash(struct evm_ima_xattr_data *hdr, enum hash_algo *algo,
+ const u8 **hash, u8 *len)
+{
+ struct modsig_hdr *modsig = (typeof(modsig)) hdr;
+ const struct public_key_signature *pks;
+ int i;
+
+ if (!hdr || hdr->type != IMA_MODSIG)
+ return -EINVAL;
+
+ 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;
+
+ return pkcs7_get_digest(modsig->pkcs7_msg, hash, len);
+}
+
+int ima_modsig_serialize_data(struct evm_ima_xattr_data **data, int *data_len)
+{
+ struct modsig_hdr *modsig = (struct modsig_hdr *) *data;
+
+ if (!*data || (*data)->type != IMA_MODSIG)
+ return -EINVAL;
+
+ *data = &modsig->raw_pkcs7;
+ *data_len = modsig->raw_pkcs7_len;
+
+ 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 *keyring;
+
+ if (!hdr || hdr->type != IMA_MODSIG)
+ return -EINVAL;
+
+ keyring = integrity_keyring_from_id(keyring_id);
+ if (IS_ERR(keyring))
+ return PTR_ERR(keyring);
+
+ return verify_pkcs7_message_sig(NULL, 0, modsig->pkcs7_msg, keyring,
+ 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 6643c6550787..4acb1fb86b3b 100644
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -74,6 +74,7 @@ enum evm_ima_xattr_type {
EVM_IMA_XATTR_DIGSIG,
IMA_XATTR_DIGEST_NG,
EVM_XATTR_PORTABLE_DIGSIG,
+ IMA_MODSIG,
IMA_XATTR_LAST
};

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