apparmor: add the ability to report a sha1 hash of loaded policy

Provide userspace the ability to introspect a sha1 hash value for each
profile currently loaded.

Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Seth Arnold <seth.arnold@canonical.com>

security/apparmor/crypto.c

@@ -0,0 +1,97 @@
+/*
+ * AppArmor security module
+ *
+ * This file contains AppArmor policy loading interface function definitions.
+ *
+ * Copyright 2013 Canonical Ltd.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation, version 2 of the
+ * License.
+ *
+ * Fns to provide a checksum of policy that has been loaded this can be
+ * compared to userspace policy compiles to check loaded policy is what
+ * it should be.
+ */
+
+#include <linux/crypto.h>
+
+#include "include/apparmor.h"
+#include "include/crypto.h"
+
+static unsigned int apparmor_hash_size;
+
+static struct crypto_hash *apparmor_tfm;
+
+unsigned int aa_hash_size(void)
+{
+	return apparmor_hash_size;
+}
+
+int aa_calc_profile_hash(struct aa_profile *profile, u32 version, void *start,
+			 size_t len)
+{
+	struct scatterlist sg[2];
+	struct hash_desc desc = {
+		.tfm = apparmor_tfm,
+		.flags = 0
+	};
+	int error = -ENOMEM;
+	u32 le32_version = cpu_to_le32(version);
+
+	if (!apparmor_tfm)
+		return 0;
+
+	sg_init_table(sg, 2);
+	sg_set_buf(&sg[0], &le32_version, 4);
+	sg_set_buf(&sg[1], (u8 *) start, len);
+
+	profile->hash = kzalloc(apparmor_hash_size, GFP_KERNEL);
+	if (!profile->hash)
+		goto fail;
+
+	error = crypto_hash_init(&desc);
+	if (error)
+		goto fail;
+	error = crypto_hash_update(&desc, &sg[0], 4);
+	if (error)
+		goto fail;
+	error = crypto_hash_update(&desc, &sg[1], len);
+	if (error)
+		goto fail;
+	error = crypto_hash_final(&desc, profile->hash);
+	if (error)
+		goto fail;
+
+	return 0;
+
+fail:
+	kfree(profile->hash);
+	profile->hash = NULL;
+
+	return error;
+}
+
+static int __init init_profile_hash(void)
+{
+	struct crypto_hash *tfm;
+
+	if (!apparmor_initialized)
+		return 0;
+
+	tfm = crypto_alloc_hash("sha1", 0, CRYPTO_ALG_ASYNC);
+	if (IS_ERR(tfm)) {
+		int error = PTR_ERR(tfm);
+		AA_ERROR("failed to setup profile sha1 hashing: %d\n", error);
+		return error;
+	}
+	apparmor_tfm = tfm;
+	apparmor_hash_size = crypto_hash_digestsize(apparmor_tfm);
+
+	aa_info_message("AppArmor sha1 policy hashing enabled");
+
+	return 0;
+}
+
+late_initcall(init_profile_hash);