apparmor: Initial support for compressed policies

This patch allows policies to be compressed in userspace and be sent to
the kernel through the existing ".load" and ".replace" kernel interfaces.

The benefits of this approach are:
 - Save kernel time when loading policies
 - Allow userspace to provide a higher level of compression than the one
   provided by the kernel (ZSTD_CLEVEL_DEFAULT), thus saving space.
 - Allow small embedded systems to only store the compressed version of
   policies in userspace, saving memory.

Userspace-compressed policies improve system time by up to ~30% for big
profiles.

Signed-off-by: Maxime Bélair <maxime.belair@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/apparmorfs.c

@@ -482,6 +482,69 @@ static struct aa_loaddata *aa_simple_write_to_buffer(const char __user *userbuf,
 
 	return data;
 }
+static int decompress_zstd(char *src, size_t slen, char *dst, size_t dlen);
+/**
+ * aa_get_data_from_compressed - common routine for getting compressed policy
+ * from user and get both compressed and uncompressed version.
+ * @userbuf: user buffer to copy data from  (NOT NULL)
+ * @buffer_size: size of user buffer
+ * @pos: position write is at in the file (NOT NULL)
+ * @compressed_data Ptr on compressed data. *compressed_data is allocated there
+ *
+ * Returns: kernel buffer containing copy of user buffer data or an
+ *          ERR_PTR on failure.
+ */
+
+static struct aa_loaddata *aa_get_data_from_compressed(const char __user *userbuf,
+						  size_t buffer_size,
+						  loff_t *pos,
+						  char **compressed_data)
+{
+	struct aa_loaddata *data;
+	zstd_frame_header header;
+	int error;
+
+	if (!userbuf || !pos)
+		return ERR_PTR(-EINVAL);
+	if (*pos)
+		return ERR_PTR(-ESPIPE);
+
+	*compressed_data = kvmalloc(buffer_size, GFP_KERNEL);
+	if (!*compressed_data)
+		return ERR_PTR(-ENOMEM);
+	error = copy_from_user(*compressed_data, userbuf, buffer_size);
+	if (error)
+		goto fail;
+
+	error = zstd_get_frame_header(&header, *compressed_data, buffer_size);
+	if (error || header.frameContentSize == ZSTD_CONTENTSIZE_UNKNOWN ||
+	    header.frameContentSize == ZSTD_CONTENTSIZE_ERROR) {
+		error = -EINVAL;
+		goto fail;
+	}
+
+	data = aa_loaddata_alloc(header.frameContentSize);
+	if (IS_ERR(data)) {
+		error = PTR_ERR(data);
+		goto fail;
+	}
+
+	// We then decompress the data
+	error = decompress_zstd(*compressed_data, buffer_size, data->data,
+				header.frameContentSize);
+	if (error)
+		goto fail_decompress;
+
+	data->size = header.frameContentSize;
+	return data;
+
+fail_decompress:
+	aa_put_i_loaddata(data);
+fail:
+	kvfree(*compressed_data);
+	return ERR_PTR(error);
+
+}
 
 static ssize_t policy_update(u32 mask, const char __user *buf, size_t size,
 			     loff_t *pos, struct aa_ns *ns,
@@ -490,6 +553,9 @@ static ssize_t policy_update(u32 mask, const char __user *buf, size_t size,
 	struct aa_loaddata *data;
 	struct aa_label *label;
 	ssize_t error;
+	char *compressed_data = NULL;
+	__le32 magic_le;
+	bool is_compressed;
 
 	label = begin_current_label_crit_section();
 
@@ -500,10 +566,33 @@ static ssize_t policy_update(u32 mask, const char __user *buf, size_t size,
 	if (error)
 		goto end_section;
 
-	data = aa_simple_write_to_buffer(buf, size, size, pos);
-	error = PTR_ERR(data);
+	/* If the policy is userspace compressed we start by decompressing it
+	 * to make the required checks (computing hash, verifying profile, ...)
+	 *
+	 * Getting a userspace-compressed version then decompressing it in the
+	 * kernel actually makes sense since zstd decompression is ~3.5x faster
+	 * than compression. This also allow to increase the compression level.
+	 */
+
+	if (size >= sizeof(__le32) &&
+	    !copy_from_user(&magic_le, buf, sizeof(magic_le)) &&
+	    le32_to_cpu(magic_le) == ZSTD_MAGICNUMBER)
+		is_compressed = true;
+	else
+		is_compressed = false;
+
+	if (is_compressed) {
+
+		data = aa_get_data_from_compressed(buf, size, pos, &compressed_data);
+		error = PTR_ERR(data);
+	} else {
+		data = aa_simple_write_to_buffer(buf, size, size, pos);
+		error = PTR_ERR(data);
+	}
+
 	if (!IS_ERR(data)) {
-		error = aa_replace_profiles(ns, label, mask, data);
+		error = aa_replace_profiles(ns, label, mask, data,
+					    compressed_data, size);
 		/* put pcount, which will put count and free if no
 		 * profiles referencing it.
 		 */
@@ -550,6 +639,7 @@ static const struct file_operations aa_fs_profile_replace = {
 	.llseek = default_llseek,
 };
 
+
 /* .remove file hook fn to remove loaded policy */
 static ssize_t profile_remove(struct file *f, const char __user *buf,
 			      size_t size, loff_t *pos)
@@ -2484,6 +2574,7 @@ static struct aa_sfs_entry aa_sfs_entry_policy[] = {
 	AA_SFS_FILE_STRING("permstable32", PERMS32STR),
 	AA_SFS_FILE_U64("state32",	1),
 	AA_SFS_DIR("unconfined_restrictions",   aa_sfs_entry_unconfined),
+	AA_SFS_FILE_BOOLEAN("compressed_load",	1),
 	{ }
 };
 

security/apparmor/include/policy.h

@@ -304,7 +304,8 @@ struct aa_profile *aa_fqlookupn_profile(struct aa_label *base,
 					const char *fqname, size_t n);
 
 ssize_t aa_replace_profiles(struct aa_ns *view, struct aa_label *label,
-			    u32 mask, struct aa_loaddata *udata);
+			    u32 mask, struct aa_loaddata *udata,
+			    char *compressed_profile, size_t compressed_size);
 ssize_t aa_remove_profiles(struct aa_ns *view, struct aa_label *label,
 			   char *name, size_t size);
 void __aa_profile_list_release(struct list_head *head);

security/apparmor/include/policy_unpack.h

@@ -129,7 +129,8 @@ struct aa_loaddata {
 	char *data;
 };
 
-int aa_unpack(struct aa_loaddata *udata, struct list_head *lh, const char **ns);
+int aa_unpack(struct aa_loaddata *udata, struct list_head *lh, const char **ns,
+	      char *compressed_data, size_t compressed_size);
 
 /**
  * aa_get_i_loaddata - get a reference count from a counted data reference

security/apparmor/policy.c

@@ -1159,6 +1159,8 @@ static struct aa_profile *update_to_newest_parent(struct aa_profile *new)
  * @label: label that is attempting to load/replace policy
  * @mask: permission mask
  * @udata: serialized data stream  (NOT NULL)
+ * @compressed_profile: The userspace-provided compressed profile. May be NULL
+ * @compressed_size: If compressed_data is not NULL, the compressed data size
  *
  * unpack and replace a profile on the profile list and uses of that profile
  * by any task creds via invalidating the old version of the profile, which
@@ -1168,7 +1170,8 @@ static struct aa_profile *update_to_newest_parent(struct aa_profile *new)
  * Returns: size of data consumed else error code on failure.
  */
 ssize_t aa_replace_profiles(struct aa_ns *policy_ns, struct aa_label *label,
-			    u32 mask, struct aa_loaddata *udata)
+			    u32 mask, struct aa_loaddata *udata,
+			    char *compressed_profile, size_t compressed_size)
 {
 	const char *ns_name = NULL, *info = NULL;
 	struct aa_ns *ns = NULL;
@@ -1181,7 +1184,7 @@ ssize_t aa_replace_profiles(struct aa_ns *policy_ns, struct aa_label *label,
 	op = mask & AA_MAY_REPLACE_POLICY ? OP_PROF_REPL : OP_PROF_LOAD;
 	aa_get_profile_loaddata(udata);
 	/* released below */
-	error = aa_unpack(udata, &lh, &ns_name);
+	error = aa_unpack(udata, &lh, &ns_name, compressed_profile, compressed_size);
 	if (error)
 		goto out;
 

security/apparmor/policy_unpack.c

@@ -1718,6 +1718,8 @@ static int compress_loaddata(struct aa_loaddata *data)
  * @udata: user data copied to kmem  (NOT NULL)
  * @lh: list to place unpacked profiles in a aa_repl_ws
  * @ns: Returns namespace profile is in if specified else NULL (NOT NULL)
+ * @compressed_data: The userspace-provided compressed data. May be NULL
+ * @compressed_size: If compressed_data is not NULL, the compressed data size
  *
  * Unpack user data and return refcounted allocated profile(s) stored in
  * @lh in order of discovery, with the list chain stored in base.list
@@ -1726,12 +1728,12 @@ static int compress_loaddata(struct aa_loaddata *data)
  * Returns: profile(s) on @lh else error pointer if fails to unpack
  */
 int aa_unpack(struct aa_loaddata *udata, struct list_head *lh,
-	      const char **ns)
+	      const char **ns, char *compressed_data, size_t compressed_size)
 {
 	struct aa_load_ent *tmp, *ent;
 	struct aa_profile *profile = NULL;
 	char *ns_name = NULL;
-	int error;
+	int error = 0;
 	struct aa_ext e = {
 		.start = udata->data,
 		.end = udata->data + udata->size,
@@ -1784,10 +1786,23 @@ int aa_unpack(struct aa_loaddata *udata, struct list_head *lh,
 	}
 
 	if (aa_g_export_binary) {
-		error = compress_loaddata(udata);
+		/* Do we have userspace-compressed data? */
+		if (compressed_data) {
+			kvfree(udata->data);
+			udata->data = compressed_data;
+			udata->compressed_size = compressed_size;
+			compressed_data = NULL; /* consumed */
+
+		} else
+			error = compress_loaddata(udata);
+
 		if (error)
 			goto fail;
+	} else if (compressed_data) {
+		kvfree(compressed_data);
+		compressed_data = NULL;
 	}
+
 	return 0;
 
 fail_profile:
@@ -1795,6 +1810,8 @@ fail_profile:
 	aa_put_profile(profile);
 
 fail:
+	if (compressed_data)
+		kvfree(compressed_data);
 	list_for_each_entry_safe(ent, tmp, lh, list) {
 		list_del_init(&ent->list);
 		aa_load_ent_free(ent);