From 38349552d8d6418229fee9ee68b1f470b4ad7a52 Mon Sep 17 00:00:00 2001
From: Daniel Mack <daniel@zonque.org>
Date: Fri, 19 Sep 2014 14:38:52 +0200
Subject: [PATCH] bus-policy: add policy check function
Add policy_check() to actually check whether an incoming message is allowed
by the policy. The code is not yet used from the proxy daemon, though.
---
src/bus-proxyd/bus-policy.c | 156 ++++++++++++++++++++++++++++++++++++++++++++
src/bus-proxyd/bus-policy.h | 2 +
2 files changed, 158 insertions(+)
diff --git a/src/bus-proxyd/bus-policy.c b/src/bus-proxyd/bus-policy.c
index e870fbc948..151d679f6b 100644
--- a/src/bus-proxyd/bus-policy.c
+++ b/src/bus-proxyd/bus-policy.c
@@ -24,6 +24,7 @@
#include "strv.h"
#include "conf-files.h"
#include "bus-internal.h"
+#include "bus-message.h"
#include "bus-policy.h"
static void policy_item_free(PolicyItem *i) {
@@ -591,6 +592,161 @@ static int file_load(Policy *p, const char *path) {
}
}
+static bool is_matching_name_request(sd_bus_message *m, const char *name, bool prefix) {
+
+ char *n = NULL;
+ int r;
+
+ if (!sd_bus_message_is_method_call(m, "org.freedesktop.DBus", "RequestName"))
+ return false;
+
+ r = sd_bus_message_read(m, "s", &n);
+ if (r < 0)
+ return false;
+
+ r = sd_bus_message_rewind(m, true);
+ if (r < 0)
+ return false;
+
+ if (prefix)
+ return startswith(name, n);
+ else
+ return streq_ptr(name, n);
+}
+
+static bool is_matching_call(PolicyItem *i, sd_bus_message *m, const char *name) {
+
+ if (i->message_type && (i->message_type != m->header->type))
+ return false;
+
+ if (i->path && (!m->path || !streq(i->path, m->path)))
+ return false;
+
+ if (i->member && (!m->member || !streq(i->member, m->member)))
+ return false;
+
+ if (i->interface && (!m->interface || !streq(i->interface, m->interface)))
+ return false;
+
+ if (i->name && (!name || !streq(i->name, name)))
+ return false;
+
+ return true;
+}
+
+enum {
+ ALLOW,
+ DUNNO,
+ DENY,
+};
+
+static int is_permissive(PolicyItem *i) {
+
+ return (i->type == POLICY_ITEM_ALLOW) ? ALLOW : DENY;
+}
+
+static int check_policy_item(PolicyItem *i, sd_bus_message *m, const struct ucred *ucred) {
+
+ switch (i->class) {
+ case POLICY_ITEM_SEND:
+ if ((m->bus->is_kernel && is_matching_call(i, m, m->destination)) ||
+ (!m->bus->is_kernel && is_matching_call(i, m, m->sender)))
+ return is_permissive(i);
+ break;
+
+ case POLICY_ITEM_RECV:
+ if ((m->bus->is_kernel && is_matching_call(i, m, m->sender)) ||
+ (!m->bus->is_kernel && is_matching_call(i, m, m->destination)))
+ return is_permissive(i);
+ break;
+
+ case POLICY_ITEM_OWN:
+ if (is_matching_name_request(m, i->name, false))
+ return is_permissive(i);
+ break;
+
+ case POLICY_ITEM_OWN_PREFIX:
+ if (is_matching_name_request(m, i->name, true))
+ return is_permissive(i);
+ break;
+
+ case POLICY_ITEM_USER:
+ if (sd_bus_message_is_method_call(m, "org.freedesktop.DBus", "Hello") &&
+ (streq_ptr(i->name, "*") || (i->uid_valid && i->uid == ucred->uid)))
+ return is_permissive(i);
+ break;
+
+ case POLICY_ITEM_GROUP:
+ if (sd_bus_message_is_method_call(m, "org.freedesktop.DBus", "Hello") &&
+ (streq_ptr(i->name, "*") || (i->gid_valid && i->gid == ucred->gid)))
+ return is_permissive(i);
+ break;
+
+ case POLICY_ITEM_IGNORE:
+ default:
+ break;
+ }
+
+ return DUNNO;
+}
+
+static int check_policy_items(PolicyItem *items, sd_bus_message *m, const struct ucred *ucred) {
+
+ PolicyItem *i;
+ int r, ret = DUNNO;
+
+ /* Check all policies in a set - a broader one might be followed by a more specific one,
+ * and the order of rules in policy definitions matters */
+ LIST_FOREACH(items, i, items) {
+ r = check_policy_item(i, m, ucred);
+ if (r != DUNNO)
+ ret = r;
+ }
+
+ return ret;
+}
+
+bool policy_check(Policy *p, sd_bus_message *m, const struct ucred *ucred) {
+
+ PolicyItem *items;
+ int r;
+
+ /*
+ * The policy check is implemented by the following logic:
+ *
+ * 1. Check mandatory items. If the message matches any of these, it is decisive.
+ * 2. See if the passed ucred match against the user/group hashmaps. A matching entry is also decisive.
+ * 3. Consult the defaults if non of the above matched with a more specific rule.
+ * 4. If the message isn't caught be the defaults either, reject it.
+ */
+
+ r = check_policy_items(p->mandatory_items, m, ucred);
+ if (r != DUNNO)
+ return r == ALLOW;
+
+ if (ucred->pid > 0) {
+ items = hashmap_get(p->user_items, UINT32_TO_PTR(ucred->uid));
+ if (items) {
+ r = check_policy_items(items, m, ucred);
+ if (r != DUNNO)
+ return r == ALLOW;
+ }
+
+ items = hashmap_get(p->group_items, UINT32_TO_PTR(ucred->gid));
+ if (items) {
+ r = check_policy_items(items, m, ucred);
+ if (r != DUNNO)
+ return r == ALLOW;
+ }
+ }
+
+ r = check_policy_items(p->default_items, m, ucred);
+ if (r != DUNNO)
+ return r == ALLOW;
+
+ return false;
+}
+
int policy_load(Policy *p, char **files) {
char **i;
int r;
diff --git a/src/bus-proxyd/bus-policy.h b/src/bus-proxyd/bus-policy.h
index a6ff5c37f6..2222716e7a 100644
--- a/src/bus-proxyd/bus-policy.h
+++ b/src/bus-proxyd/bus-policy.h
@@ -76,6 +76,8 @@ typedef struct Policy {
int policy_load(Policy *p, char **files);
void policy_free(Policy *p);
+bool policy_check(Policy *p, sd_bus_message *m, const struct ucred *c);
+
void policy_dump(Policy *p);
const char* policy_item_type_to_string(PolicyItemType t) _const_;