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/Kconfig

@@ -29,3 +29,15 @@ config SECURITY_APPARMOR_BOOTPARAM_VALUE
 	  boot.
 
 	  If you are unsure how to answer this question, answer 1.
+
+config SECURITY_APPARMOR_HASH
+	bool "SHA1 hash of loaded profiles"
+	depends on SECURITY_APPARMOR
+	depends on CRYPTO
+	select CRYPTO_SHA1
+	default y
+
+	help
+	  This option selects whether sha1 hashing is done against loaded
+          profiles and exported for inspection to user space via the apparmor
+          filesystem.

security/apparmor/Makefile

@@ -5,6 +5,7 @@ obj-$(CONFIG_SECURITY_APPARMOR) += apparmor.o
 apparmor-y := apparmorfs.o audit.o capability.o context.o ipc.o lib.o match.o \
               path.o domain.o policy.o policy_unpack.o procattr.o lsm.o \
               resource.o sid.o file.o
+apparmor-$(CONFIG_SECURITY_APPARMOR_HASH) += crypto.o
 
 clean-files := capability_names.h rlim_names.h
 

security/apparmor/apparmorfs.c

@@ -26,6 +26,7 @@
 #include "include/apparmorfs.h"
 #include "include/audit.h"
 #include "include/context.h"
+#include "include/crypto.h"
 #include "include/policy.h"
 #include "include/resource.h"
 
@@ -319,6 +320,34 @@ static const struct file_operations aa_fs_profattach_fops = {
 	.release	= aa_fs_seq_profile_release,
 };
 
+static int aa_fs_seq_hash_show(struct seq_file *seq, void *v)
+{
+	struct aa_replacedby *r = seq->private;
+	struct aa_profile *profile = aa_get_profile_rcu(&r->profile);
+	unsigned int i, size = aa_hash_size();
+
+	if (profile->hash) {
+		for (i = 0; i < size; i++)
+			seq_printf(seq, "%.2x", profile->hash[i]);
+		seq_puts(seq, "\n");
+	}
+
+	return 0;
+}
+
+static int aa_fs_seq_hash_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, aa_fs_seq_hash_show, inode->i_private);
+}
+
+static const struct file_operations aa_fs_seq_hash_fops = {
+	.owner		= THIS_MODULE,
+	.open		= aa_fs_seq_hash_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
 /** fns to setup dynamic per profile/namespace files **/
 void __aa_fs_profile_rmdir(struct aa_profile *profile)
 {
@@ -420,6 +449,14 @@ int __aa_fs_profile_mkdir(struct aa_profile *profile, struct dentry *parent)
 		goto fail;
 	profile->dents[AAFS_PROF_ATTACH] = dent;
 
+	if (profile->hash) {
+		dent = create_profile_file(dir, "sha1", profile,
+					   &aa_fs_seq_hash_fops);
+		if (IS_ERR(dent))
+			goto fail;
+		profile->dents[AAFS_PROF_HASH] = dent;
+	}
+
 	list_for_each_entry(child, &profile->base.profiles, base.list) {
 		error = __aa_fs_profile_mkdir(child, prof_child_dir(profile));
 		if (error)

security/apparmor/crypto.c

+/*
+ * 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);

security/apparmor/include/apparmorfs.h

@@ -82,6 +82,7 @@ enum aafs_prof_type {
 	AAFS_PROF_NAME,
 	AAFS_PROF_MODE,
 	AAFS_PROF_ATTACH,
+	AAFS_PROF_HASH,
 	AAFS_PROF_SIZEOF,
 };
 

security/apparmor/include/crypto.h

+/*
+ * 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.
+ */
+
+#ifndef __APPARMOR_CRYPTO_H
+#define __APPARMOR_CRYPTO_H
+
+#include "policy.h"
+
+#ifdef CONFIG_SECURITY_APPARMOR_HASH
+unsigned int aa_hash_size(void);
+int aa_calc_profile_hash(struct aa_profile *profile, u32 version, void *start,
+			 size_t len);
+#else
+static inline int aa_calc_profile_hash(struct aa_profile *profile, u32 version,
+				       void *start, size_t len)
+{
+	return 0;
+}
+
+static inline unsigned int aa_hash_size(void)
+{
+	return 0;
+}
+#endif
+
+#endif /* __APPARMOR_CRYPTO_H */

security/apparmor/include/policy.h

@@ -219,6 +219,7 @@ struct aa_profile {
 	struct aa_caps caps;
 	struct aa_rlimit rlimits;
 
+	unsigned char *hash;
 	char *dirname;
 	struct dentry *dents[AAFS_PROF_SIZEOF];
 };

security/apparmor/policy_unpack.c

@@ -24,6 +24,7 @@
 #include "include/apparmor.h"
 #include "include/audit.h"
 #include "include/context.h"
+#include "include/crypto.h"
 #include "include/match.h"
 #include "include/policy.h"
 #include "include/policy_unpack.h"
@@ -758,10 +759,12 @@ int aa_unpack(void *udata, size_t size, struct list_head *lh, const char **ns)
 
 	*ns = NULL;
 	while (e.pos < e.end) {
+		void *start;
 		error = verify_header(&e, e.pos == e.start, ns);
 		if (error)
 			goto fail;
 
+		start = e.pos;
 		profile = unpack_profile(&e);
 		if (IS_ERR(profile)) {
 			error = PTR_ERR(profile);
@@ -769,16 +772,18 @@ int aa_unpack(void *udata, size_t size, struct list_head *lh, const char **ns)
 		}
 
 		error = verify_profile(profile);
-		if (error) {
-			aa_free_profile(profile);
-			goto fail;
-		}
+		if (error)
+			goto fail_profile;
+
+		error = aa_calc_profile_hash(profile, e.version, start,
+					     e.pos - start);
+		if (error)
+			goto fail_profile;
 
 		ent = aa_load_ent_alloc();
 		if (!ent) {
 			error = -ENOMEM;
-			aa_put_profile(profile);
-			goto fail;
+			goto fail_profile;
 		}
 
 		ent->new = profile;
@@ -787,6 +792,9 @@ int aa_unpack(void *udata, size_t size, struct list_head *lh, const char **ns)
 
 	return 0;
 
+fail_profile:
+	aa_put_profile(profile);
+
 fail:
 	list_for_each_entry_safe(ent, tmp, lh, list) {
 		list_del_init(&ent->list);