service_manager.c revision c67e6307cadb1f2cd876907c42d39b8374b93acd 
1/* Copyright 2008 The Android Open Source Project
2 */
3
4#include <stdio.h>
5#include <stdlib.h>
6#include <errno.h>
7#include <fcntl.h>
8
9#include <private/android_filesystem_config.h>
10
11#include <selinux/android.h>
12#include <selinux/avc.h>
13
14#include "binder.h"
15
16#if 0
17#define ALOGI(x...) fprintf(stderr, "svcmgr: " x)
18#define ALOGE(x...) fprintf(stderr, "svcmgr: " x)
19#else
20#define LOG_TAG "ServiceManager"
21#include <cutils/log.h>
22#endif
23
24uint32_t svcmgr_handle;
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;
173
174    if (!svc_can_find(s, len, spid)) {
175        ALOGE("find_service('%s') uid=%d - PERMISSION DENIED\n",
176             str8(s, len), uid);
177        return 0;
178    }
179    si = find_svc(s, len);
180    //ALOGI("check_service('%s') handle = %x\n", str8(s, len), si ? si->handle : 0);
181    if (si && si->handle) {
182        if (!si->allow_isolated) {
183            // If this service doesn't allow access from isolated processes,
184            // then check the uid to see if it is isolated.
185            uid_t appid = uid % AID_USER;
186            if (appid >= AID_ISOLATED_START && appid <= AID_ISOLATED_END) {
187                return 0;
188            }
189        }
190        return si->handle;
191    } else {
192        return 0;
193    }
194}
195
196int do_add_service(struct binder_state *bs,
197                   const uint16_t *s, size_t len,
198                   uint32_t handle, uid_t uid, int allow_isolated,
199                   pid_t spid)
200{
201    struct svcinfo *si;
202
203    //ALOGI("add_service('%s',%x,%s) uid=%d\n", str8(s, len), handle,
204    //        allow_isolated ? "allow_isolated" : "!allow_isolated", uid);
205
206    if (!handle || (len == 0) || (len > 127))
207        return -1;
208
209    if (!svc_can_register(s, len, spid)) {
210        ALOGE("add_service('%s',%x) uid=%d - PERMISSION DENIED\n",
211             str8(s, len), handle, uid);
212        return -1;
213    }
214
215    si = find_svc(s, len);
216    if (si) {
217        if (si->handle) {
218            ALOGE("add_service('%s',%x) uid=%d - ALREADY REGISTERED, OVERRIDE\n",
219                 str8(s, len), handle, uid);
220            svcinfo_death(bs, si);
221        }
222        si->handle = handle;
223    } else {
224        si = malloc(sizeof(*si) + (len + 1) * sizeof(uint16_t));
225        if (!si) {
226            ALOGE("add_service('%s',%x) uid=%d - OUT OF MEMORY\n",
227                 str8(s, len), handle, uid);
228            return -1;
229        }
230        si->handle = handle;
231        si->len = len;
232        memcpy(si->name, s, (len + 1) * sizeof(uint16_t));
233        si->name[len] = '\0';
234        si->death.func = (void*) svcinfo_death;
235        si->death.ptr = si;
236        si->allow_isolated = allow_isolated;
237        si->next = svclist;
238        svclist = si;
239    }
240
241    binder_acquire(bs, handle);
242    binder_link_to_death(bs, handle, &si->death);
243    return 0;
244}
245
246int svcmgr_handler(struct binder_state *bs,
247                   struct binder_transaction_data *txn,
248                   struct binder_io *msg,
249                   struct binder_io *reply)
250{
251    struct svcinfo *si;
252    uint16_t *s;
253    size_t len;
254    uint32_t handle;
255    uint32_t strict_policy;
256    int allow_isolated;
257
258    //ALOGI("target=%x code=%d pid=%d uid=%d\n",
259    //  txn->target.handle, txn->code, txn->sender_pid, txn->sender_euid);
260
261    if (txn->target.handle != svcmgr_handle)
262        return -1;
263
264    if (txn->code == PING_TRANSACTION)
265        return 0;
266
267    // Equivalent to Parcel::enforceInterface(), reading the RPC
268    // header with the strict mode policy mask and the interface name.
269    // Note that we ignore the strict_policy and don't propagate it
270    // further (since we do no outbound RPCs anyway).
271    strict_policy = bio_get_uint32(msg);
272    s = bio_get_string16(msg, &len);
273    if (s == NULL) {
274        return -1;
275    }
276
277    if ((len != (sizeof(svcmgr_id) / 2)) ||
278        memcmp(svcmgr_id, s, sizeof(svcmgr_id))) {
279        fprintf(stderr,"invalid id %s\n", str8(s, len));
280        return -1;
281    }
282
283    if (sehandle && selinux_status_updated() > 0) {
284        struct selabel_handle *tmp_sehandle = selinux_android_service_context_handle();
285        if (tmp_sehandle) {
286            selabel_close(sehandle);
287            sehandle = tmp_sehandle;
288        }
289    }
290
291    switch(txn->code) {
292    case SVC_MGR_GET_SERVICE:
293    case SVC_MGR_CHECK_SERVICE:
294        s = bio_get_string16(msg, &len);
295        if (s == NULL) {
296            return -1;
297        }
298        handle = do_find_service(bs, s, len, txn->sender_euid, txn->sender_pid);
299        if (!handle)
300            break;
301        bio_put_ref(reply, handle);
302        return 0;
303
304    case SVC_MGR_ADD_SERVICE:
305        s = bio_get_string16(msg, &len);
306        if (s == NULL) {
307            return -1;
308        }
309        handle = bio_get_ref(msg);
310        allow_isolated = bio_get_uint32(msg) ? 1 : 0;
311        if (do_add_service(bs, s, len, handle, txn->sender_euid,
312            allow_isolated, txn->sender_pid))
313            return -1;
314        break;
315
316    case SVC_MGR_LIST_SERVICES: {
317        uint32_t n = bio_get_uint32(msg);
318
319        if (!svc_can_list(txn->sender_pid)) {
320            ALOGE("list_service() uid=%d - PERMISSION DENIED\n",
321                    txn->sender_euid);
322            return -1;
323        }
324        si = svclist;
325        while ((n-- > 0) && si)
326            si = si->next;
327        if (si) {
328            bio_put_string16(reply, si->name);
329            return 0;
330        }
331        return -1;
332    }
333    default:
334        ALOGE("unknown code %d\n", txn->code);
335        return -1;
336    }
337
338    bio_put_uint32(reply, 0);
339    return 0;
340}
341
342
343static int audit_callback(void *data, security_class_t cls, char *buf, size_t len)
344{
345    snprintf(buf, len, "service=%s", !data ? "NULL" : (char *)data);
346    return 0;
347}
348
349int main(int argc, char **argv)
350{
351    struct binder_state *bs;
352
353    bs = binder_open(128*1024);
354    if (!bs) {
355        ALOGE("failed to open binder driver\n");
356        return -1;
357    }
358
359    if (binder_become_context_manager(bs)) {
360        ALOGE("cannot become context manager (%s)\n", strerror(errno));
361        return -1;
362    }
363
364    selinux_enabled = is_selinux_enabled();
365    sehandle = selinux_android_service_context_handle();
366
367    if (selinux_enabled > 0) {
368        if (sehandle == NULL) {
369            ALOGE("SELinux: Failed to acquire sehandle. Aborting.\n");
370            abort();
371        }
372
373        if (getcon(&service_manager_context) != 0) {
374            ALOGE("SELinux: Failed to acquire service_manager context. Aborting.\n");
375            abort();
376        }
377    }
378
379    union selinux_callback cb;
380    cb.func_audit = audit_callback;
381    selinux_set_callback(SELINUX_CB_AUDIT, cb);
382    cb.func_log = selinux_log_callback;
383    selinux_set_callback(SELINUX_CB_LOG, cb);
384
385    svcmgr_handle = BINDER_SERVICE_MANAGER;
386    binder_loop(bs, svcmgr_handler);
387
388    return 0;
389}
390