1 /*
2 * Copyright (C) 2016 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #define LOG_TAG "keystore"
18
19 #include "permissions.h"
20
21 #include <cutils/log.h>
22 #include <cutils/sockets.h>
23 #include <private/android_filesystem_config.h>
24
25 #include <selinux/android.h>
26
27 #include "keystore_utils.h"
28
29 /* perm_labels associcated with keystore_key SELinux class verbs. */
30 const char* perm_labels[] = {
31 "get_state", "get", "insert", "delete", "exist", "list",
32 "reset", "password", "lock", "unlock", "is_empty", "sign",
33 "verify", "grant", "duplicate", "clear_uid", "add_auth", "user_changed",
34 };
35
36 struct user_euid {
37 uid_t uid;
38 uid_t euid;
39 };
40
41 user_euid user_euids[] = {
42 {AID_VPN, AID_SYSTEM}, {AID_WIFI, AID_SYSTEM}, {AID_ROOT, AID_SYSTEM},
43 };
44
45 struct user_perm {
46 uid_t uid;
47 perm_t perms;
48 };
49
50 static user_perm user_perms[] = {
51 {AID_SYSTEM, static_cast<perm_t>((uint32_t)(~0))},
52 {AID_VPN, static_cast<perm_t>(P_GET | P_SIGN | P_VERIFY)},
53 {AID_WIFI, static_cast<perm_t>(P_GET | P_SIGN | P_VERIFY)},
54 {AID_ROOT, static_cast<perm_t>(P_GET)},
55 };
56
57 static const perm_t DEFAULT_PERMS = static_cast<perm_t>(P_GET_STATE | P_GET | P_INSERT | P_DELETE |
58 P_EXIST | P_LIST | P_SIGN | P_VERIFY);
59
60 struct audit_data {
61 pid_t pid;
62 uid_t uid;
63 };
64
get_perm_label(perm_t perm)65 const char* get_perm_label(perm_t perm) {
66 unsigned int index = ffs(perm);
67 if (index > 0 && index <= (sizeof(perm_labels) / sizeof(perm_labels[0]))) {
68 return perm_labels[index - 1];
69 } else {
70 ALOGE("Keystore: Failed to retrieve permission label.\n");
71 abort();
72 }
73 }
74
audit_callback(void * data,security_class_t,char * buf,size_t len)75 static int audit_callback(void* data, security_class_t /* cls */, char* buf, size_t len) {
76 struct audit_data* ad = reinterpret_cast<struct audit_data*>(data);
77 if (!ad) {
78 ALOGE("No keystore audit data");
79 return 0;
80 }
81
82 snprintf(buf, len, "pid=%d uid=%d", ad->pid, ad->uid);
83 return 0;
84 }
85
86 static char* tctx;
87 static int ks_is_selinux_enabled;
88
configure_selinux()89 int configure_selinux() {
90 ks_is_selinux_enabled = is_selinux_enabled();
91 if (ks_is_selinux_enabled) {
92 union selinux_callback cb;
93 cb.func_audit = audit_callback;
94 selinux_set_callback(SELINUX_CB_AUDIT, cb);
95 cb.func_log = selinux_log_callback;
96 selinux_set_callback(SELINUX_CB_LOG, cb);
97 if (getcon(&tctx) != 0) {
98 ALOGE("SELinux: Could not acquire target context. Aborting keystore.\n");
99 return -1;
100 }
101 } else {
102 ALOGI("SELinux: Keystore SELinux is disabled.\n");
103 }
104
105 return 0;
106 }
107
keystore_selinux_check_access(uid_t uid,perm_t perm,pid_t spid)108 static bool keystore_selinux_check_access(uid_t uid, perm_t perm, pid_t spid) {
109 if (!ks_is_selinux_enabled) {
110 return true;
111 }
112
113 audit_data ad;
114 char* sctx = NULL;
115 const char* selinux_class = "keystore_key";
116 const char* str_perm = get_perm_label(perm);
117
118 if (!str_perm) {
119 return false;
120 }
121
122 if (getpidcon(spid, &sctx) != 0) {
123 ALOGE("SELinux: Failed to get source pid context.\n");
124 return false;
125 }
126
127 ad.pid = spid;
128 ad.uid = uid;
129
130 bool allowed = selinux_check_access(sctx, tctx, selinux_class, str_perm,
131 reinterpret_cast<void*>(&ad)) == 0;
132 freecon(sctx);
133 return allowed;
134 }
135
136 /**
137 * Returns the UID that the callingUid should act as. This is here for
138 * legacy support of the WiFi and VPN systems and should be removed
139 * when WiFi can operate in its own namespace.
140 */
get_keystore_euid(uid_t uid)141 uid_t get_keystore_euid(uid_t uid) {
142 for (size_t i = 0; i < sizeof(user_euids) / sizeof(user_euids[0]); i++) {
143 struct user_euid user = user_euids[i];
144 if (user.uid == uid) {
145 return user.euid;
146 }
147 }
148
149 return uid;
150 }
151
has_permission(uid_t uid,perm_t perm,pid_t spid)152 bool has_permission(uid_t uid, perm_t perm, pid_t spid) {
153 // All system users are equivalent for multi-user support.
154 if (get_app_id(uid) == AID_SYSTEM) {
155 uid = AID_SYSTEM;
156 }
157
158 for (size_t i = 0; i < sizeof(user_perms) / sizeof(user_perms[0]); i++) {
159 struct user_perm user = user_perms[i];
160 if (user.uid == uid) {
161 return (user.perms & perm) && keystore_selinux_check_access(uid, perm, spid);
162 }
163 }
164
165 return (DEFAULT_PERMS & perm) && keystore_selinux_check_access(uid, perm, spid);
166 }
167
168 /**
169 * Returns true if the callingUid is allowed to interact in the targetUid's
170 * namespace.
171 */
is_granted_to(uid_t callingUid,uid_t targetUid)172 bool is_granted_to(uid_t callingUid, uid_t targetUid) {
173 if (callingUid == targetUid) {
174 return true;
175 }
176 for (size_t i = 0; i < sizeof(user_euids) / sizeof(user_euids[0]); i++) {
177 struct user_euid user = user_euids[i];
178 if (user.euid == callingUid && user.uid == targetUid) {
179 return true;
180 }
181 }
182
183 return false;
184 }
185