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. */
30const 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
36struct user_euid {
37    uid_t uid;
38    uid_t euid;
39};
40
41user_euid user_euids[] = {
42    {AID_VPN, AID_SYSTEM}, {AID_WIFI, AID_SYSTEM}, {AID_ROOT, AID_SYSTEM},
43};
44
45struct user_perm {
46    uid_t uid;
47    perm_t perms;
48};
49
50static 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
57static 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
60struct audit_data {
61    pid_t pid;
62    uid_t uid;
63};
64
65const 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
75static 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
86static char* tctx;
87static int ks_is_selinux_enabled;
88
89int 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
108static 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 */
141uid_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
152bool 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 */
172bool 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