kdbus: add policy database implementation

[Greg Kroah-Hartman]

From: Daniel Mack <daniel@xxxxxxxxxx>

This patch adds the policy database implementation.

A policy databases restrict 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 Documentation/kdbus.txt for more details.

Signed-off-by: Daniel Mack <daniel@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/misc/kdbus/policy.c | 617 ++++++++++++++++++++++++++++++++++++++++++++
 drivers/misc/kdbus/policy.h |  60 +++++
 2 files changed, 677 insertions(+)
 create mode 100644 drivers/misc/kdbus/policy.c
 create mode 100644 drivers/misc/kdbus/policy.h

diff --git a/drivers/misc/kdbus/policy.c b/drivers/misc/kdbus/policy.c
new file mode 100644
index 000000000000..66bce57eb5e6
--- /dev/null
+++ b/drivers/misc/kdbus/policy.c
@@ -0,0 +1,617 @@
+/*
+ * Copyright (C) 2013-2014 Kay Sievers
+ * Copyright (C) 2013-2014 Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
+ * Copyright (C) 2013-2014 Daniel Mack <daniel@xxxxxxxxxx>
+ * Copyright (C) 2013-2014 David Herrmann <dh.herrmann@xxxxxxxxx>
+ * Copyright (C) 2013-2014 Linux Foundation
+ * Copyright (C) 2014 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/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_cache_entry - a cached entry
+ * @conn_a:		Connection A
+ * @conn_b:		Connection B
+ * @owner:		Owner of policy-entry that produced this cache-entry
+ * @hentry:		The hash table entry for the database's entries_hash
+ */
+struct kdbus_policy_db_cache_entry {
+	struct kdbus_conn *conn_a;
+	struct kdbus_conn *conn_b;
+	const void *owner;
+	struct hlist_node hentry;
+};
+
+/**
+ * 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 const struct kdbus_policy_db_entry *
+kdbus_policy_lookup(struct kdbus_policy_db *db,
+		    const char *name, u32 hash, bool wildcard)
+{
+	struct kdbus_policy_db_entry *e, *found = NULL;
+
+	hash_for_each_possible(db->entries_hash, e, hentry, hash)
+		if (strcmp(e->name, name) == 0 && !e->wildcard)
+			return e;
+
+	if (wildcard) {
+		const char *tmp;
+		char *dot;
+
+		tmp = kstrdup(name, GFP_KERNEL);
+		if (!tmp)
+			return NULL;
+
+		dot = strrchr(tmp, '.');
+		if (!dot)
+			goto exit_free;
+
+		*dot = '\0';
+		hash = kdbus_str_hash(tmp);
+
+		hash_for_each_possible(db->entries_hash, e, hentry, hash)
+			if (strcmp(e->name, tmp) == 0 && e->wildcard) {
+				found = e;
+				/* never "break;" in hash_for_each() */
+				goto exit_free;
+			}
+
+exit_free:
+		kfree(tmp);
+	}
+
+	return found;
+}
+
+/**
+ * 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_cache_entry *ce;
+	struct kdbus_policy_db_entry *e;
+	struct hlist_node *tmp;
+	unsigned int i;
+
+	BUG_ON(!db);
+
+	/* 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);
+
+	/* purge cache */
+	mutex_lock(&db->cache_lock);
+	hash_for_each_safe(db->talk_access_hash, i, tmp, ce, hentry) {
+		hash_del(&ce->hentry);
+		kfree(ce);
+	}
+	mutex_unlock(&db->cache_lock);
+}
+
+/**
+ * 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);
+	hash_init(db->talk_access_hash);
+	init_rwsem(&db->entries_rwlock);
+	mutex_init(&db->cache_lock);
+}
+
+static int kdbus_policy_check_access(const struct kdbus_policy_db_entry *e,
+				     const struct cred *cred,
+				     unsigned int access)
+{
+	struct kdbus_policy_db_entry_access *a;
+	struct group_info *group_info;
+	int i;
+
+	if (!e)
+		return -EPERM;
+
+	group_info = cred->group_info;
+
+	list_for_each_entry(a, &e->access_list, list) {
+		if (a->access >= access) {
+			switch (a->type) {
+			case KDBUS_POLICY_ACCESS_USER:
+				if (uid_eq(cred->uid, a->uid))
+					return 0;
+				break;
+			case KDBUS_POLICY_ACCESS_GROUP:
+				if (gid_eq(cred->gid, a->gid))
+					return 0;
+
+				for (i = 0; i < group_info->ngroups; i++) {
+					kgid_t gid = GROUP_AT(group_info, i);
+
+					if (gid_eq(gid, a->gid))
+						return 0;
+				}
+
+				break;
+			case KDBUS_POLICY_ACCESS_WORLD:
+				return 0;
+			}
+		}
+	}
+
+	return -EPERM;
+}
+
+/**
+ * kdbus_policy_check_own_access() - check whether a connection is allowed
+ *				     to own a name
+ * @db:		The policy database
+ * @conn:	The connection to check
+ * @name:	The name to check
+ *
+ * Return: 0 if the connection is allowed to own the name, -EPERM otherwise
+ */
+int kdbus_policy_check_own_access(struct kdbus_policy_db *db,
+				  const struct kdbus_conn *conn,
+				  const char *name)
+{
+	const struct kdbus_policy_db_entry *e;
+	int ret;
+
+	down_read(&db->entries_rwlock);
+	e = kdbus_policy_lookup(db, name, kdbus_str_hash(name), true);
+	ret = kdbus_policy_check_access(e, conn->cred, KDBUS_POLICY_OWN);
+	up_read(&db->entries_rwlock);
+
+	return ret;
+}
+
+/**
+ * kdbus_policy_check_talk_access() - check if one connection is allowed
+ *				       to send a message to another connection
+ * @db:			The policy database
+ * @conn_src:		The source connection
+ * @conn_dst:		The destination connection
+ *
+ * Return: 0 if access is granted, -EPERM if not, negative errno on failure
+ */
+int kdbus_policy_check_talk_access(struct kdbus_policy_db *db,
+				   struct kdbus_conn *conn_src,
+				   struct kdbus_conn *conn_dst)
+{
+	struct kdbus_policy_db_cache_entry *ce;
+	struct kdbus_name_entry *name_entry;
+	unsigned int hash = 0;
+	const void *owner;
+	int ret;
+
+	/*
+	 * If there was a positive match for these two connections before,
+	 * there's an entry in the hash table for them.
+	 */
+	hash ^= hash_ptr(conn_src, KDBUS_POLICY_HASH_SIZE);
+	hash ^= hash_ptr(conn_dst, KDBUS_POLICY_HASH_SIZE);
+
+	mutex_lock(&db->cache_lock);
+	hash_for_each_possible(db->talk_access_hash, ce, hentry, hash)
+		if (ce->conn_a == conn_src && ce->conn_b == conn_dst) {
+			mutex_unlock(&db->cache_lock);
+			return 0;
+		}
+	mutex_unlock(&db->cache_lock);
+
+	/*
+	 * Otherwise, walk the connection list and store a hash-table entry if
+	 * send access is granted.
+	 */
+
+	down_read(&db->entries_rwlock);
+
+	ret = -EPERM;
+	mutex_lock(&conn_dst->lock);
+	list_for_each_entry(name_entry, &conn_dst->names_list, conn_entry) {
+		u32 hash = kdbus_str_hash(name_entry->name);
+		const struct kdbus_policy_db_entry *e;
+
+		e = kdbus_policy_lookup(db, name_entry->name, hash, true);
+		if (kdbus_policy_check_access(e, conn_src->cred,
+					      KDBUS_POLICY_TALK) == 0) {
+			owner = e->owner;
+			ret = 0;
+			break;
+		}
+	}
+	mutex_unlock(&conn_dst->lock);
+
+	if (ret >= 0) {
+		ret = -ENOMEM;
+		ce = kmalloc(sizeof(*ce), GFP_KERNEL);
+		if (ce) {
+			ce->conn_a = conn_src;
+			ce->conn_b = conn_dst;
+			ce->owner = owner;
+			INIT_HLIST_NODE(&ce->hentry);
+
+			mutex_lock(&db->cache_lock);
+			hash_add(db->talk_access_hash, &ce->hentry, hash);
+			mutex_unlock(&db->cache_lock);
+
+			ret = 0;
+		}
+	}
+
+	up_read(&db->entries_rwlock);
+
+	return ret;
+}
+
+/**
+ * kdbus_policy_check_see_access_unlocked() - Check whether a connection is
+ *					      allowed to see a given name
+ * @db:		The policy database
+ * @conn:	The connection performing the lookup
+ * @name:	The name
+ *
+ * Return: 0 if permission to see the name is granted, -EPERM otherwise
+ */
+int kdbus_policy_check_see_access_unlocked(struct kdbus_policy_db *db,
+					   struct kdbus_conn *conn,
+					   const char *name)
+{
+	const struct kdbus_policy_db_entry *e;
+
+	e = kdbus_policy_lookup(db, name, kdbus_str_hash(name), true);
+	return kdbus_policy_check_access(e, conn->cred, KDBUS_POLICY_SEE);
+}
+
+static void __kdbus_policy_remove_owner_cache(struct kdbus_policy_db *db,
+					      const void *owner)
+{
+	struct kdbus_policy_db_cache_entry *ce;
+	struct hlist_node *tmp;
+	int i;
+
+	mutex_lock(&db->cache_lock);
+	hash_for_each_safe(db->talk_access_hash, i, tmp, ce, hentry)
+		if (ce->owner == owner) {
+			hash_del(&ce->hentry);
+			kfree(ce);
+		}
+	mutex_unlock(&db->cache_lock);
+}
+
+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);
+	__kdbus_policy_remove_owner_cache(db, owner);
+	up_write(&db->entries_rwlock);
+}
+
+/**
+ * kdbus_policy_purge_cache_for_conn() - remove all cached entries related to
+ *				a connection
+ * @db:		The policy database
+ * @conn:	The connection which items to remove
+ */
+void kdbus_policy_purge_cache(struct kdbus_policy_db *db,
+			      const struct kdbus_conn *conn)
+{
+	struct kdbus_policy_db_cache_entry *ce;
+	struct hlist_node *tmp;
+	int i;
+
+	mutex_lock(&db->cache_lock);
+	hash_for_each_safe(db->talk_access_hash, i, tmp, ce, hentry)
+		if (ce->conn_a == conn || ce->conn_b == conn) {
+			hash_del(&ce->hentry);
+			kfree(ce);
+		}
+	mutex_unlock(&db->cache_lock);
+}
+
+/*
+ * Convert user provided policy access to internal kdbus policy
+ * access
+ */
+static int
+kdbus_policy_make_access(const struct kdbus_policy_access *uaccess,
+			 struct kdbus_policy_db_entry_access **entry)
+{
+	int ret;
+	struct kdbus_policy_db_entry_access *a;
+
+	a = kzalloc(sizeof(*a), GFP_KERNEL);
+	if (!a)
+		return -ENOMEM;
+
+	ret = -EINVAL;
+	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;
+	}
+
+	a->type = uaccess->type;
+	a->access = uaccess->access;
+
+	*entry = a;
+
+	return 0;
+
+err:
+	kfree(a);
+	return 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.
+ *
+ * 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;
+
+	if (items_size > KDBUS_POLICY_MAX_SIZE)
+		return -E2BIG;
+
+	/* 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;
+			}
+
+			ret = kdbus_policy_make_access(&item->policy_access,
+						       &a);
+			if (ret < 0)
+				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_str_hash(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);
+	}
+
+	/* purge all cache-entries produced by previous rules */
+	__kdbus_policy_remove_owner_cache(db, owner);
+
+restore:
+	/* if we failed, flush all entries we added so far, but keep cache */
+	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_str_hash(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/drivers/misc/kdbus/policy.h b/drivers/misc/kdbus/policy.h
new file mode 100644
index 000000000000..f4f6f044b4c1
--- /dev/null
+++ b/drivers/misc/kdbus/policy.h
@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2013-2014 Kay Sievers
+ * Copyright (C) 2013-2014 Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
+ * Copyright (C) 2013-2014 Daniel Mack <daniel@xxxxxxxxxx>
+ * Copyright (C) 2013-2014 David Herrmann <dh.herrmann@xxxxxxxxx>
+ * Copyright (C) 2013-2014 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/mutex.h>
+#include <linux/rwsem.h>
+
+struct kdbus_conn;
+struct kdbus_item;
+
+/**
+ * struct kdbus_policy_db - policy database
+ * @entries_hash:	Hashtable of entries
+ * @talk_access_hash:	Hashtable of send access elements
+ * @entries_lock:	Mutex to protect the database's access entries
+ * @cache_lock:		Mutex to protect the database's cache
+ */
+struct kdbus_policy_db {
+	DECLARE_HASHTABLE(entries_hash, 6);
+	DECLARE_HASHTABLE(talk_access_hash, 6);
+	struct rw_semaphore entries_rwlock;
+	struct mutex cache_lock;
+};
+
+void kdbus_policy_db_init(struct kdbus_policy_db *db);
+void kdbus_policy_db_clear(struct kdbus_policy_db *db);
+
+int kdbus_policy_check_see_access_unlocked(struct kdbus_policy_db *db,
+					   struct kdbus_conn *conn,
+					   const char *name);
+int kdbus_policy_check_talk_access(struct kdbus_policy_db *db,
+				   struct kdbus_conn *conn_src,
+				   struct kdbus_conn *conn_dst);
+int kdbus_policy_check_own_access(struct kdbus_policy_db *db,
+				  const struct kdbus_conn *conn,
+				  const char *name);
+void kdbus_policy_purge_cache(struct kdbus_policy_db *db,
+			      const struct kdbus_conn *conn);
+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
-- 
2.1.2

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