service_manager.c revision bea0746b241d15626cf0a56828efc1d4640dbda7 
1/* Copyright 2008 The Android Open Source Project
2 */
3
4#include <errno.h>
5#include <fcntl.h>
6#include <inttypes.h>
7#include <stdio.h>
8#include <stdlib.h>
9#include <string.h>
10
11#include <private/android_filesystem_config.h>
12
13#include <selinux/android.h>
14#include <selinux/avc.h>
15
16#include "binder.h"
17
18#if 0
19#define ALOGI(x...) fprintf(stderr, "svcmgr: " x)
20#define ALOGE(x...) fprintf(stderr, "svcmgr: " x)
21#else
22#define LOG_TAG "ServiceManager"
23#include <cutils/log.h>
24#endif
25
26const char *str8(const uint16_t *x, size_t x_len)
27{
28    static char buf[128];
29    size_t max = 127;
30    char *p = buf;
31
32    if (x_len < max) {
33        max = x_len;
34    }
35
36    if (x) {
37        while ((max > 0) && (*x != '\0')) {
38            *p++ = *x++;
39            max--;
40        }
41    }
42    *p++ = 0;
43    return buf;
44}
45
46int str16eq(const uint16_t *a, const char *b)
47{
48    while (*a && *b)
49        if (*a++ != *b++) return 0;
50    if (*a || *b)
51        return 0;
52    return 1;
53}
54
55static int selinux_enabled;
56static char *service_manager_context;
57static struct selabel_handle* sehandle;
58
59static bool check_mac_perms(pid_t spid, const char *tctx, const char *perm, const char *name)
60{
61    char *sctx = NULL;
62    const char *class = "service_manager";
63    bool allowed;
64
65    if (getpidcon(spid, &sctx) < 0) {
66        ALOGE("SELinux: getpidcon(pid=%d) failed to retrieve pid context.\n", spid);
67        return false;
68    }
69
70    int result = selinux_check_access(sctx, tctx, class, perm, (void *) name);
71    allowed = (result == 0);
72
73    freecon(sctx);
74    return allowed;
75}
76
77static bool check_mac_perms_from_getcon(pid_t spid, const char *perm)
78{
79    if (selinux_enabled <= 0) {
80        return true;
81    }
82
83    return check_mac_perms(spid, service_manager_context, perm, NULL);
84}
85
86static bool check_mac_perms_from_lookup(pid_t spid, const char *perm, const char *name)
87{
88    bool allowed;
89    char *tctx = NULL;
90
91    if (selinux_enabled <= 0) {
92        return true;
93    }
94
95    if (!sehandle) {
96        ALOGE("SELinux: Failed to find sehandle. Aborting service_manager.\n");
97        abort();
98    }
99
100    if (selabel_lookup(sehandle, &tctx, name, 0) != 0) {
101        ALOGE("SELinux: No match for %s in service_contexts.\n", name);
102        return false;
103    }
104
105    allowed = check_mac_perms(spid, tctx, perm, name);
106    freecon(tctx);
107    return allowed;
108}
109
110static int svc_can_register(const uint16_t *name, size_t name_len, pid_t spid)
111{
112    const char *perm = "add";
113    return check_mac_perms_from_lookup(spid, perm, str8(name, name_len)) ? 1 : 0;
114}
115
116static int svc_can_list(pid_t spid)
117{
118    const char *perm = "list";
119    return check_mac_perms_from_getcon(spid, perm) ? 1 : 0;
120}
121
122static int svc_can_find(const uint16_t *name, size_t name_len, pid_t spid)
123{
124    const char *perm = "find";
125    return check_mac_perms_from_lookup(spid, perm, str8(name, name_len)) ? 1 : 0;
126}
127
128struct svcinfo
129{
130    struct svcinfo *next;
131    uint32_t handle;
132    struct binder_death death;
133    int allow_isolated;
134    size_t len;
135    uint16_t name[0];
136};
137
138struct svcinfo *svclist = NULL;
139
140struct svcinfo *find_svc(const uint16_t *s16, size_t len)
141{
142    struct svcinfo *si;
143
144    for (si = svclist; si; si = si->next) {
145        if ((len == si->len) &&
146            !memcmp(s16, si->name, len * sizeof(uint16_t))) {
147            return si;
148        }
149    }
150    return NULL;
151}
152
153void svcinfo_death(struct binder_state *bs, void *ptr)
154{
155    struct svcinfo *si = (struct svcinfo* ) ptr;
156
157    ALOGI("service '%s' died\n", str8(si->name, si->len));
158    if (si->handle) {
159        binder_release(bs, si->handle);
160        si->handle = 0;
161    }
162}
163
164uint16_t svcmgr_id[] = {
165    'a','n','d','r','o','i','d','.','o','s','.',
166    'I','S','e','r','v','i','c','e','M','a','n','a','g','e','r'
167};
168
169
170uint32_t do_find_service(struct binder_state *bs, const uint16_t *s, size_t len, uid_t uid, pid_t spid)
171{
172    struct svcinfo *si = find_svc(s, len);
173
174    if (!si || !si->handle) {
175        return 0;
176    }
177
178    if (!si->allow_isolated) {
179        // If this service doesn't allow access from isolated processes,
180        // then check the uid to see if it is isolated.
181        uid_t appid = uid % AID_USER;
182        if (appid >= AID_ISOLATED_START && appid <= AID_ISOLATED_END) {
183            return 0;
184        }
185    }
186
187    if (!svc_can_find(s, len, spid)) {
188        return 0;
189    }
190
191    return si->handle;
192}
193
194int do_add_service(struct binder_state *bs,
195                   const uint16_t *s, size_t len,
196                   uint32_t handle, uid_t uid, int allow_isolated,
197                   pid_t spid)
198{
199    struct svcinfo *si;
200
201    //ALOGI("add_service('%s',%x,%s) uid=%d\n", str8(s, len), handle,
202    //        allow_isolated ? "allow_isolated" : "!allow_isolated", uid);
203
204    if (!handle || (len == 0) || (len > 127))
205        return -1;
206
207    if (!svc_can_register(s, len, spid)) {
208        ALOGE("add_service('%s',%x) uid=%d - PERMISSION DENIED\n",
209             str8(s, len), handle, uid);
210        return -1;
211    }
212
213    si = find_svc(s, len);
214    if (si) {
215        if (si->handle) {
216            ALOGE("add_service('%s',%x) uid=%d - ALREADY REGISTERED, OVERRIDE\n",
217                 str8(s, len), handle, uid);
218            svcinfo_death(bs, si);
219        }
220        si->handle = handle;
221    } else {
222        si = malloc(sizeof(*si) + (len + 1) * sizeof(uint16_t));
223        if (!si) {
224            ALOGE("add_service('%s',%x) uid=%d - OUT OF MEMORY\n",
225                 str8(s, len), handle, uid);
226            return -1;
227        }
228        si->handle = handle;
229        si->len = len;
230        memcpy(si->name, s, (len + 1) * sizeof(uint16_t));
231        si->name[len] = '\0';
232        si->death.func = (void*) svcinfo_death;
233        si->death.ptr = si;
234        si->allow_isolated = allow_isolated;
235        si->next = svclist;
236        svclist = si;
237    }
238
239    binder_acquire(bs, handle);
240    binder_link_to_death(bs, handle, &si->death);
241    return 0;
242}
243
244int svcmgr_handler(struct binder_state *bs,
245                   struct binder_transaction_data *txn,
246                   struct binder_io *msg,
247                   struct binder_io *reply)
248{
249    struct svcinfo *si;
250    uint16_t *s;
251    size_t len;
252    uint32_t handle;
253    uint32_t strict_policy;
254    int allow_isolated;
255
256    //ALOGI("target=%p code=%d pid=%d uid=%d\n",
257    //      (void*) txn->target.ptr, txn->code, txn->sender_pid, txn->sender_euid);
258
259    if (txn->target.ptr != BINDER_SERVICE_MANAGER)
260        return -1;
261
262    if (txn->code == PING_TRANSACTION)
263        return 0;
264
265    // Equivalent to Parcel::enforceInterface(), reading the RPC
266    // header with the strict mode policy mask and the interface name.
267    // Note that we ignore the strict_policy and don't propagate it
268    // further (since we do no outbound RPCs anyway).
269    strict_policy = bio_get_uint32(msg);
270    s = bio_get_string16(msg, &len);
271    if (s == NULL) {
272        return -1;
273    }
274
275    if ((len != (sizeof(svcmgr_id) / 2)) ||
276        memcmp(svcmgr_id, s, sizeof(svcmgr_id))) {
277        fprintf(stderr,"invalid id %s\n", str8(s, len));
278        return -1;
279    }
280
281    if (sehandle && selinux_status_updated() > 0) {
282        struct selabel_handle *tmp_sehandle = selinux_android_service_context_handle();
283        if (tmp_sehandle) {
284            selabel_close(sehandle);
285            sehandle = tmp_sehandle;
286        }
287    }
288
289    switch(txn->code) {
290    case SVC_MGR_GET_SERVICE:
291    case SVC_MGR_CHECK_SERVICE:
292        s = bio_get_string16(msg, &len);
293        if (s == NULL) {
294            return -1;
295        }
296        handle = do_find_service(bs, s, len, txn->sender_euid, txn->sender_pid);
297        if (!handle)
298            break;
299        bio_put_ref(reply, handle);
300        return 0;
301
302    case SVC_MGR_ADD_SERVICE:
303        s = bio_get_string16(msg, &len);
304        if (s == NULL) {
305            return -1;
306        }
307        handle = bio_get_ref(msg);
308        allow_isolated = bio_get_uint32(msg) ? 1 : 0;
309        if (do_add_service(bs, s, len, handle, txn->sender_euid,
310            allow_isolated, txn->sender_pid))
311            return -1;
312        break;
313
314    case SVC_MGR_LIST_SERVICES: {
315        uint32_t n = bio_get_uint32(msg);
316
317        if (!svc_can_list(txn->sender_pid)) {
318            ALOGE("list_service() uid=%d - PERMISSION DENIED\n",
319                    txn->sender_euid);
320            return -1;
321        }
322        si = svclist;
323        while ((n-- > 0) && si)
324            si = si->next;
325        if (si) {
326            bio_put_string16(reply, si->name);
327            return 0;
328        }
329        return -1;
330    }
331    default:
332        ALOGE("unknown code %d\n", txn->code);
333        return -1;
334    }
335
336    bio_put_uint32(reply, 0);
337    return 0;
338}
339
340
341static int audit_callback(void *data, security_class_t cls, char *buf, size_t len)
342{
343    snprintf(buf, len, "service=%s", !data ? "NULL" : (char *)data);
344    return 0;
345}
346
347int main(int argc, char **argv)
348{
349    struct binder_state *bs;
350
351    bs = binder_open(128*1024);
352    if (!bs) {
353        ALOGE("failed to open binder driver\n");
354        return -1;
355    }
356
357    if (binder_become_context_manager(bs)) {
358        ALOGE("cannot become context manager (%s)\n", strerror(errno));
359        return -1;
360    }
361
362    selinux_enabled = is_selinux_enabled();
363    sehandle = selinux_android_service_context_handle();
364    selinux_status_open(true);
365
366    if (selinux_enabled > 0) {
367        if (sehandle == NULL) {
368            ALOGE("SELinux: Failed to acquire sehandle. Aborting.\n");
369            abort();
370        }
371
372        if (getcon(&service_manager_context) != 0) {
373            ALOGE("SELinux: Failed to acquire service_manager context. Aborting.\n");
374            abort();
375        }
376    }
377
378    union selinux_callback cb;
379    cb.func_audit = audit_callback;
380    selinux_set_callback(SELINUX_CB_AUDIT, cb);
381    cb.func_log = selinux_log_callback;
382    selinux_set_callback(SELINUX_CB_LOG, cb);
383
384    binder_loop(bs, svcmgr_handler);
385
386    return 0;
387}
388