This patch introduces a blacklist list of kernel module's hash. It check
the blacklist before checking kernel module signature.
It didn't limit what hash algorithm used but the module of hash algorithm
need build-in or put in initrd for verify kernel module in initrd.
v2:
+ Use the digest generated by mod_make_digest() to avoid computing the hash twice.
+ Also check the hash of whole module file is not in the module hash blacklist.
+ Change the statements of information log.
Signed-off-by: Lee, Chun-Yi <jlee@xxxxxxxx>
---
kernel/module-internal.h | 14 ++++++++
kernel/module.c | 9 +++++-
kernel/module_signing.c | 79 ++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 101 insertions(+), 1 deletions(-)
Index: linux-3.12-SLE12/kernel/module-internal.h
===================================================================
--- linux-3.12-SLE12.orig/kernel/module-internal.h
+++ linux-3.12-SLE12/kernel/module-internal.h
@@ -9,4 +9,17 @@
* 2 of the Licence, or (at your option) any later version.
*/
+/*
+ * Module hash.
+ */
+struct module_hash {
+ struct list_head list; /* list of all hashs */
+ u8 hash; /* Hash algorithm [enum pkey_hash_algo] */
+ char *hash_name; /* nams string of hash */
+ size_t size; /* size of hash */
+ u8 hash_data[]; /* Hash data */
+};
+
+extern struct list_head module_hash_blacklist;
+
extern int mod_verify_sig(const void *mod, unsigned long *_modlen);
Index: linux-3.12-SLE12/kernel/module_signing.c
===================================================================
--- linux-3.12-SLE12.orig/kernel/module_signing.c
+++ linux-3.12-SLE12/kernel/module_signing.c
@@ -11,12 +11,15 @@
#include <linux/kernel.h>
#include <linux/err.h>
+#include <linux/module.h>
#include <crypto/public_key.h>
#include <crypto/hash.h>
#include <keys/asymmetric-type.h>
#include <keys/system_keyring.h>
#include "module-internal.h"
+LIST_HEAD(module_hash_blacklist);
+
/*
* Module signature information block.
*
@@ -193,6 +196,82 @@ static struct key *request_asymmetric_ke
return key_ref_to_ptr(key);
}
+static int check_blacklist(const char *hash_algo_name, const void *hash)
+{
+ struct module_hash *module_hash;
+ int ret = 0;
+
+ list_for_each_entry(module_hash, &module_hash_blacklist, list) {
+ if (strcmp(hash_algo_name, module_hash->hash_name))
+ continue;
+
+ if (!memcmp(hash, module_hash->hash_data, module_hash->size)) {
+ ret = -EKEYREJECTED;
+ pr_info("Module hash is in the module hash blacklist: "
+ "%*phN\n", (int)module_hash->size,
+ module_hash->hash_data);
+ break;
+ }
+ }
+
+ return ret;
+}
+
+static int mod_verify_hash(const void *mod, unsigned long modlen,
+ struct public_key_signature *pks)
+{
+ const char *pks_hash_algo = pkey_hash_algo_name[pks->pkey_hash_algo];
+ struct crypto_shash *tfm;
+ struct shash_desc *desc;
+ size_t digest_size, desc_size;
+ u8 *digest;
+ int ret = 0;
+
+ if (list_empty(&module_hash_blacklist))
+ return 0;
+
+ /* check digest of module is not in hash blacklist */
+ ret = check_blacklist(pks_hash_algo, pks->digest);
+ if (ret)
+ goto error_return;
+
+ /* check hash of whole module file */
+ tfm = crypto_alloc_shash(pks_hash_algo, 0, 0);
+ if (IS_ERR(tfm))
+ goto error_return;
+
+ desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
+ digest_size = crypto_shash_digestsize(tfm);
+ digest = kzalloc(digest_size + desc_size, GFP_KERNEL);
+ if (!digest) {
+ pr_err("digest memory buffer allocate fail\n");
+ ret = -ENOMEM;
+ goto error_digest;
+ }
+ desc = (void *)digest + digest_size;
+ desc->tfm = tfm;
+ desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
+ ret = crypto_shash_init(desc);
+ if (ret < 0)
+ goto error_shash;
+
+ ret = crypto_shash_finup(desc, mod, modlen, digest);
+ if (ret < 0)
+ goto error_shash;
+
+ pr_debug("%ld digest: %*phN\n", modlen, (int) digest_size, digest);
+
+ /* check the hash of whole module file including signature */
+ ret = check_blacklist(pks_hash_algo, digest);
+
+error_shash:
+ kfree(digest);
+error_digest:
+ crypto_free_shash(tfm);
+error_return:
+ return ret;
+}
+
/*
* Verify the signature on a module.
*/
@@ -202,7 +281,7 @@ int mod_verify_sig(const void *mod, unsi
struct module_signature ms;
struct key *key;
const void *sig;
- size_t modlen = *_modlen, sig_len;
+ size_t modlen = *_modlen, sig_len, wholelen;
int ret;
pr_devel("==>%s(,%zu)\n", __func__, modlen);
@@ -210,6 +289,7 @@ int mod_verify_sig(const void *mod, unsi
if (modlen <= sizeof(ms))
return -EBADMSG;
+ wholelen = modlen + sizeof(MODULE_SIG_STRING) - 1;
memcpy(&ms, mod + (modlen - sizeof(ms)), sizeof(ms));
modlen -= sizeof(ms);
@@ -252,6 +332,10 @@ int mod_verify_sig(const void *mod, unsi
ret = verify_signature(key, pks);
pr_devel("verify_signature() = %d\n", ret);
+ /* check hash of module not in blacklist */
+ if (!ret)
+ ret = mod_verify_hash(mod, wholelen, pks);
+
error_free_pks:
mpi_free(pks->rsa.s);
kfree(pks);
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