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 
str8(const uint16_t * x,size_t x_len)26 const 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 
str16eq(const uint16_t * a,const char * b)46 int 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 
55 static int selinux_enabled;
56 static char *service_manager_context;
57 static struct selabel_handle* sehandle;
58 
check_mac_perms(pid_t spid,const char * tctx,const char * perm,const char * name)59 static 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 
check_mac_perms_from_getcon(pid_t spid,const char * perm)77 static 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 
check_mac_perms_from_lookup(pid_t spid,const char * perm,const char * name)86 static 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 
svc_can_register(const uint16_t * name,size_t name_len,pid_t spid)110 static 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 
svc_can_list(pid_t spid)116 static 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 
svc_can_find(const uint16_t * name,size_t name_len,pid_t spid)122 static 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 
128 struct 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 
138 struct svcinfo *svclist = NULL;
139 
find_svc(const uint16_t * s16,size_t len)140 struct 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 
svcinfo_death(struct binder_state * bs,void * ptr)153 void 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 
164 uint16_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 
do_find_service(struct binder_state * bs,const uint16_t * s,size_t len,uid_t uid,pid_t spid)170 uint32_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 
do_add_service(struct binder_state * bs,const uint16_t * s,size_t len,uint32_t handle,uid_t uid,int allow_isolated,pid_t spid)194 int 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 
svcmgr_handler(struct binder_state * bs,struct binder_transaction_data * txn,struct binder_io * msg,struct binder_io * reply)244 int 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 
audit_callback(void * data,security_class_t cls,char * buf,size_t len)341 static 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 
main(int argc,char ** argv)347 int 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