[PATCH 11/14] kdbus: add policy database implementation

[Greg Kroah-Hartman]

From: Daniel Mack <daniel@xxxxxxxxxx>

This patch adds the policy database implementation.

A policy database restricts the possibilities of connections to own,
see and talk to well-known names. It can be associated with a bus
(through a policy holder connection) or a custom endpoint.

By default, buses have an empty policy database that is augmented on
demand when a policy holder connection is instantiated.

Policies are set through KDBUS_CMD_HELLO (when creating a policy
holder connection), KDBUS_CMD_CONN_UPDATE (when updating a policy
holder connection), KDBUS_CMD_EP_MAKE (creating a custom endpoint)
or KDBUS_CMD_EP_UPDATE (updating a custom endpoint). In all cases,
the name and policy access information is stored in items of type
KDBUS_ITEM_NAME and KDBUS_ITEM_POLICY_ACCESS.

See kdbus.policy(7) for more details.

Signed-off-by: Daniel Mack <daniel@xxxxxxxxxx>
Signed-off-by: David Herrmann <dh.herrmann@xxxxxxxxx>
Signed-off-by: Djalal Harouni <tixxdz@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 ipc/kdbus/policy.c | 489 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 ipc/kdbus/policy.h |  51 ++++++
 2 files changed, 540 insertions(+)
 create mode 100644 ipc/kdbus/policy.c
 create mode 100644 ipc/kdbus/policy.h

diff --git a/ipc/kdbus/policy.c b/ipc/kdbus/policy.c
new file mode 100644
index 000000000000..dd7fffaafa84
--- /dev/null
+++ b/ipc/kdbus/policy.c
@@ -0,0 +1,489 @@
+/*
+ * Copyright (C) 2013-2015 Kay Sievers
+ * Copyright (C) 2013-2015 Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
+ * Copyright (C) 2013-2015 Daniel Mack <daniel@xxxxxxxxxx>
+ * Copyright (C) 2013-2015 David Herrmann <dh.herrmann@xxxxxxxxx>
+ * Copyright (C) 2013-2015 Linux Foundation
+ * Copyright (C) 2014-2015 Djalal Harouni
+ *
+ * kdbus is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation; either version 2.1 of the License, or (at
+ * your option) any later version.
+ */
+
+#include <linux/dcache.h>
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/mutex.h>
+#include <linux/sched.h>
+#include <linux/sizes.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+
+#include "bus.h"
+#include "connection.h"
+#include "domain.h"
+#include "item.h"
+#include "names.h"
+#include "policy.h"
+
+#define KDBUS_POLICY_HASH_SIZE	64
+
+/**
+ * struct kdbus_policy_db_entry_access - a database entry access item
+ * @type:		One of KDBUS_POLICY_ACCESS_* types
+ * @access:		Access to grant. One of KDBUS_POLICY_*
+ * @uid:		For KDBUS_POLICY_ACCESS_USER, the global uid
+ * @gid:		For KDBUS_POLICY_ACCESS_GROUP, the global gid
+ * @list:		List entry item for the entry's list
+ *
+ * This is the internal version of struct kdbus_policy_db_access.
+ */
+struct kdbus_policy_db_entry_access {
+	u8 type;		/* USER, GROUP, WORLD */
+	u8 access;		/* OWN, TALK, SEE */
+	union {
+		kuid_t uid;	/* global uid */
+		kgid_t gid;	/* global gid */
+	};
+	struct list_head list;
+};
+
+/**
+ * struct kdbus_policy_db_entry - a policy database entry
+ * @name:		The name to match the policy entry against
+ * @hentry:		The hash entry for the database's entries_hash
+ * @access_list:	List head for keeping tracks of the entry's
+ *			access items.
+ * @owner:		The owner of this entry. Can be a kdbus_conn or
+ *			a kdbus_ep object.
+ * @wildcard:		The name is a wildcard, such as ending on '.*'
+ */
+struct kdbus_policy_db_entry {
+	char *name;
+	struct hlist_node hentry;
+	struct list_head access_list;
+	const void *owner;
+	bool wildcard:1;
+};
+
+static void kdbus_policy_entry_free(struct kdbus_policy_db_entry *e)
+{
+	struct kdbus_policy_db_entry_access *a, *tmp;
+
+	list_for_each_entry_safe(a, tmp, &e->access_list, list) {
+		list_del(&a->list);
+		kfree(a);
+	}
+
+	kfree(e->name);
+	kfree(e);
+}
+
+static unsigned int kdbus_strnhash(const char *str, size_t len)
+{
+	unsigned long hash = init_name_hash();
+
+	while (len--)
+		hash = partial_name_hash(*str++, hash);
+
+	return end_name_hash(hash);
+}
+
+static const struct kdbus_policy_db_entry *
+kdbus_policy_lookup(struct kdbus_policy_db *db, const char *name, u32 hash)
+{
+	struct kdbus_policy_db_entry *e;
+	const char *dot;
+	size_t len;
+
+	/* find exact match */
+	hash_for_each_possible(db->entries_hash, e, hentry, hash)
+		if (strcmp(e->name, name) == 0 && !e->wildcard)
+			return e;
+
+	/* find wildcard match */
+
+	dot = strrchr(name, '.');
+	if (!dot)
+		return NULL;
+
+	len = dot - name;
+	hash = kdbus_strnhash(name, len);
+
+	hash_for_each_possible(db->entries_hash, e, hentry, hash)
+		if (e->wildcard && !strncmp(e->name, name, len) &&
+		    !e->name[len])
+			return e;
+
+	return NULL;
+}
+
+/**
+ * kdbus_policy_db_clear - release all memory from a policy db
+ * @db:		The policy database
+ */
+void kdbus_policy_db_clear(struct kdbus_policy_db *db)
+{
+	struct kdbus_policy_db_entry *e;
+	struct hlist_node *tmp;
+	unsigned int i;
+
+	/* purge entries */
+	down_write(&db->entries_rwlock);
+	hash_for_each_safe(db->entries_hash, i, tmp, e, hentry) {
+		hash_del(&e->hentry);
+		kdbus_policy_entry_free(e);
+	}
+	up_write(&db->entries_rwlock);
+}
+
+/**
+ * kdbus_policy_db_init() - initialize a new policy database
+ * @db:		The location of the database
+ *
+ * This initializes a new policy-db. The underlying memory must have been
+ * cleared to zero by the caller.
+ */
+void kdbus_policy_db_init(struct kdbus_policy_db *db)
+{
+	hash_init(db->entries_hash);
+	init_rwsem(&db->entries_rwlock);
+}
+
+/**
+ * kdbus_policy_query_unlocked() - Query the policy database
+ * @db:		Policy database
+ * @cred:	Credentials to test against
+ * @name:	Name to query
+ * @hash:	Hash value of @name
+ *
+ * Same as kdbus_policy_query() but requires the caller to lock the policy
+ * database against concurrent writes.
+ *
+ * Return: The highest KDBUS_POLICY_* access type found, or -EPERM if none.
+ */
+int kdbus_policy_query_unlocked(struct kdbus_policy_db *db,
+				const struct cred *cred, const char *name,
+				unsigned int hash)
+{
+	struct kdbus_policy_db_entry_access *a;
+	const struct kdbus_policy_db_entry *e;
+	int i, highest = -EPERM;
+
+	e = kdbus_policy_lookup(db, name, hash);
+	if (!e)
+		return -EPERM;
+
+	list_for_each_entry(a, &e->access_list, list) {
+		if ((int)a->access <= highest)
+			continue;
+
+		switch (a->type) {
+		case KDBUS_POLICY_ACCESS_USER:
+			if (uid_eq(cred->euid, a->uid))
+				highest = a->access;
+			break;
+		case KDBUS_POLICY_ACCESS_GROUP:
+			if (gid_eq(cred->egid, a->gid)) {
+				highest = a->access;
+				break;
+			}
+
+			for (i = 0; i < cred->group_info->ngroups; i++) {
+				kgid_t gid = GROUP_AT(cred->group_info, i);
+
+				if (gid_eq(gid, a->gid)) {
+					highest = a->access;
+					break;
+				}
+			}
+
+			break;
+		case KDBUS_POLICY_ACCESS_WORLD:
+			highest = a->access;
+			break;
+		}
+
+		/* OWN is the highest possible policy */
+		if (highest >= KDBUS_POLICY_OWN)
+			break;
+	}
+
+	return highest;
+}
+
+/**
+ * kdbus_policy_query() - Query the policy database
+ * @db:		Policy database
+ * @cred:	Credentials to test against
+ * @name:	Name to query
+ * @hash:	Hash value of @name
+ *
+ * Query the policy database @db for the access rights of @cred to the name
+ * @name. The access rights of @cred are returned, or -EPERM if no access is
+ * granted.
+ *
+ * This call effectively searches for the highest access-right granted to
+ * @cred. The caller should really cache those as policy lookups are rather
+ * expensive.
+ *
+ * Return: The highest KDBUS_POLICY_* access type found, or -EPERM if none.
+ */
+int kdbus_policy_query(struct kdbus_policy_db *db, const struct cred *cred,
+		       const char *name, unsigned int hash)
+{
+	int ret;
+
+	down_read(&db->entries_rwlock);
+	ret = kdbus_policy_query_unlocked(db, cred, name, hash);
+	up_read(&db->entries_rwlock);
+
+	return ret;
+}
+
+static void __kdbus_policy_remove_owner(struct kdbus_policy_db *db,
+					const void *owner)
+{
+	struct kdbus_policy_db_entry *e;
+	struct hlist_node *tmp;
+	int i;
+
+	hash_for_each_safe(db->entries_hash, i, tmp, e, hentry)
+		if (e->owner == owner) {
+			hash_del(&e->hentry);
+			kdbus_policy_entry_free(e);
+		}
+}
+
+/**
+ * kdbus_policy_remove_owner() - remove all entries related to a connection
+ * @db:		The policy database
+ * @owner:	The connection which items to remove
+ */
+void kdbus_policy_remove_owner(struct kdbus_policy_db *db,
+			       const void *owner)
+{
+	down_write(&db->entries_rwlock);
+	__kdbus_policy_remove_owner(db, owner);
+	up_write(&db->entries_rwlock);
+}
+
+/*
+ * Convert user provided policy access to internal kdbus policy
+ * access
+ */
+static struct kdbus_policy_db_entry_access *
+kdbus_policy_make_access(const struct kdbus_policy_access *uaccess)
+{
+	int ret;
+	struct kdbus_policy_db_entry_access *a;
+
+	a = kzalloc(sizeof(*a), GFP_KERNEL);
+	if (!a)
+		return ERR_PTR(-ENOMEM);
+
+	ret = -EINVAL;
+	switch (uaccess->access) {
+	case KDBUS_POLICY_SEE:
+	case KDBUS_POLICY_TALK:
+	case KDBUS_POLICY_OWN:
+		a->access = uaccess->access;
+		break;
+	default:
+		goto err;
+	}
+
+	switch (uaccess->type) {
+	case KDBUS_POLICY_ACCESS_USER:
+		a->uid = make_kuid(current_user_ns(), uaccess->id);
+		if (!uid_valid(a->uid))
+			goto err;
+
+		break;
+	case KDBUS_POLICY_ACCESS_GROUP:
+		a->gid = make_kgid(current_user_ns(), uaccess->id);
+		if (!gid_valid(a->gid))
+			goto err;
+
+		break;
+	case KDBUS_POLICY_ACCESS_WORLD:
+		break;
+	default:
+		goto err;
+	}
+
+	a->type = uaccess->type;
+
+	return a;
+
+err:
+	kfree(a);
+	return ERR_PTR(ret);
+}
+
+/**
+ * kdbus_policy_set() - set a connection's policy rules
+ * @db:				The policy database
+ * @items:			A list of kdbus_item elements that contain both
+ *				names and access rules to set.
+ * @items_size:			The total size of the items.
+ * @max_policies:		The maximum number of policy entries to allow.
+ *				Pass 0 for no limit.
+ * @allow_wildcards:		Boolean value whether wildcard entries (such
+ *				ending on '.*') should be allowed.
+ * @owner:			The owner of the new policy items.
+ *
+ * This function sets a new set of policies for a given owner. The names and
+ * access rules are gathered by walking the list of items passed in as
+ * argument. An item of type KDBUS_ITEM_NAME is expected before any number of
+ * KDBUS_ITEM_POLICY_ACCESS items. If there are more repetitions of this
+ * pattern than denoted in @max_policies, -EINVAL is returned.
+ *
+ * In order to allow atomic replacement of rules, the function first removes
+ * all entries that have been created for the given owner previously.
+ *
+ * Callers to this function must make sur that the owner is a custom
+ * endpoint, or if the endpoint is a default endpoint, then it must be
+ * either a policy holder or an activator.
+ *
+ * Return: 0 on success, negative errno on failure.
+ */
+int kdbus_policy_set(struct kdbus_policy_db *db,
+		     const struct kdbus_item *items,
+		     size_t items_size,
+		     size_t max_policies,
+		     bool allow_wildcards,
+		     const void *owner)
+{
+	struct kdbus_policy_db_entry_access *a;
+	struct kdbus_policy_db_entry *e, *p;
+	const struct kdbus_item *item;
+	struct hlist_node *tmp;
+	HLIST_HEAD(entries);
+	HLIST_HEAD(restore);
+	size_t count = 0;
+	int i, ret = 0;
+	u32 hash;
+
+	/* Walk the list of items and look for new policies */
+	e = NULL;
+	KDBUS_ITEMS_FOREACH(item, items, items_size) {
+		switch (item->type) {
+		case KDBUS_ITEM_NAME: {
+			size_t len;
+
+			if (max_policies && ++count > max_policies) {
+				ret = -E2BIG;
+				goto exit;
+			}
+
+			if (!kdbus_name_is_valid(item->str, true)) {
+				ret = -EINVAL;
+				goto exit;
+			}
+
+			e = kzalloc(sizeof(*e), GFP_KERNEL);
+			if (!e) {
+				ret = -ENOMEM;
+				goto exit;
+			}
+
+			INIT_LIST_HEAD(&e->access_list);
+			e->owner = owner;
+			hlist_add_head(&e->hentry, &entries);
+
+			e->name = kstrdup(item->str, GFP_KERNEL);
+			if (!e->name) {
+				ret = -ENOMEM;
+				goto exit;
+			}
+
+			/*
+			 * If a supplied name ends with an '.*', cut off that
+			 * part, only store anything before it, and mark the
+			 * entry as wildcard.
+			 */
+			len = strlen(e->name);
+			if (len > 2 &&
+			    e->name[len - 3] == '.' &&
+			    e->name[len - 2] == '*') {
+				if (!allow_wildcards) {
+					ret = -EINVAL;
+					goto exit;
+				}
+
+				e->name[len - 3] = '\0';
+				e->wildcard = true;
+			}
+
+			break;
+		}
+
+		case KDBUS_ITEM_POLICY_ACCESS:
+			if (!e) {
+				ret = -EINVAL;
+				goto exit;
+			}
+
+			a = kdbus_policy_make_access(&item->policy_access);
+			if (IS_ERR(a)) {
+				ret = PTR_ERR(a);
+				goto exit;
+			}
+
+			list_add_tail(&a->list, &e->access_list);
+			break;
+		}
+	}
+
+	down_write(&db->entries_rwlock);
+
+	/* remember previous entries to restore in case of failure */
+	hash_for_each_safe(db->entries_hash, i, tmp, e, hentry)
+		if (e->owner == owner) {
+			hash_del(&e->hentry);
+			hlist_add_head(&e->hentry, &restore);
+		}
+
+	hlist_for_each_entry_safe(e, tmp, &entries, hentry) {
+		/* prevent duplicates */
+		hash = kdbus_strhash(e->name);
+		hash_for_each_possible(db->entries_hash, p, hentry, hash)
+			if (strcmp(e->name, p->name) == 0 &&
+			    e->wildcard == p->wildcard) {
+				ret = -EEXIST;
+				goto restore;
+			}
+
+		hlist_del(&e->hentry);
+		hash_add(db->entries_hash, &e->hentry, hash);
+	}
+
+restore:
+	/* if we failed, flush all entries we added so far */
+	if (ret < 0)
+		__kdbus_policy_remove_owner(db, owner);
+
+	/* if we failed, restore entries, otherwise release them */
+	hlist_for_each_entry_safe(e, tmp, &restore, hentry) {
+		hlist_del(&e->hentry);
+		if (ret < 0) {
+			hash = kdbus_strhash(e->name);
+			hash_add(db->entries_hash, &e->hentry, hash);
+		} else {
+			kdbus_policy_entry_free(e);
+		}
+	}
+
+	up_write(&db->entries_rwlock);
+
+exit:
+	hlist_for_each_entry_safe(e, tmp, &entries, hentry) {
+		hlist_del(&e->hentry);
+		kdbus_policy_entry_free(e);
+	}
+
+	return ret;
+}
diff --git a/ipc/kdbus/policy.h b/ipc/kdbus/policy.h
new file mode 100644
index 000000000000..15dd7bc12068
--- /dev/null
+++ b/ipc/kdbus/policy.h
@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2013-2015 Kay Sievers
+ * Copyright (C) 2013-2015 Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
+ * Copyright (C) 2013-2015 Daniel Mack <daniel@xxxxxxxxxx>
+ * Copyright (C) 2013-2015 David Herrmann <dh.herrmann@xxxxxxxxx>
+ * Copyright (C) 2013-2015 Linux Foundation
+ *
+ * kdbus is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation; either version 2.1 of the License, or (at
+ * your option) any later version.
+ */
+
+#ifndef __KDBUS_POLICY_H
+#define __KDBUS_POLICY_H
+
+#include <linux/hashtable.h>
+#include <linux/rwsem.h>
+
+struct kdbus_conn;
+struct kdbus_item;
+
+/**
+ * struct kdbus_policy_db - policy database
+ * @entries_hash:	Hashtable of entries
+ * @entries_rwlock:	Mutex to protect the database's access entries
+ */
+struct kdbus_policy_db {
+	DECLARE_HASHTABLE(entries_hash, 6);
+	struct rw_semaphore entries_rwlock;
+};
+
+void kdbus_policy_db_init(struct kdbus_policy_db *db);
+void kdbus_policy_db_clear(struct kdbus_policy_db *db);
+
+int kdbus_policy_query_unlocked(struct kdbus_policy_db *db,
+				const struct cred *cred, const char *name,
+				unsigned int hash);
+int kdbus_policy_query(struct kdbus_policy_db *db, const struct cred *cred,
+		       const char *name, unsigned int hash);
+
+void kdbus_policy_remove_owner(struct kdbus_policy_db *db,
+			       const void *owner);
+int kdbus_policy_set(struct kdbus_policy_db *db,
+		     const struct kdbus_item *items,
+		     size_t items_size,
+		     size_t max_policies,
+		     bool allow_wildcards,
+		     const void *owner);
+
+#endif
-- 
2.3.1

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