1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
|
/*
* Copyright (C) 2014-2021 Firejail Authors
*
* This file is part of firejail project
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include "firejail.h"
#include <sys/stat.h>
#include <sys/wait.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#ifndef O_PATH
#define O_PATH 010000000
#endif
#include <sys/prctl.h>
#ifndef PR_SET_NO_NEW_PRIVS
#define PR_SET_NO_NEW_PRIVS 38
#endif
#ifdef HAVE_APPARMOR
#include <sys/apparmor.h>
#endif
static int apply_caps = 0;
static uint64_t caps = 0;
static unsigned display = 0;
#define BUFLEN 4096
static void signal_handler(int sig){
flush_stdin();
exit(sig);
}
static void install_handler(void) {
struct sigaction sga;
// handle SIGTERM
sigemptyset(&sga.sa_mask);
sga.sa_handler = signal_handler;
sga.sa_flags = 0;
sigaction(SIGTERM, &sga, NULL);
}
#ifdef HAVE_APPARMOR
static void extract_apparmor(pid_t pid) {
if (checkcfg(CFG_APPARMOR)) {
EUID_USER();
if (aa_is_enabled() == 1) {
// get pid of next child process
pid_t child;
if (find_child(pid, &child) == 1)
child = pid; // no child, proceed with current pid
// get name of AppArmor profile
char *fname;
if (asprintf(&fname, "/proc/%d/attr/current", child) == -1)
errExit("asprintf");
EUID_ROOT();
int fd = open(fname, O_RDONLY|O_CLOEXEC);
EUID_USER();
free(fname);
if (fd == -1)
goto errexit;
char buf[BUFLEN];
ssize_t rv = read(fd, buf, sizeof(buf) - 1);
close(fd);
if (rv < 0)
goto errexit;
buf[rv] = '\0';
// process confined by Firejail's AppArmor policy?
if (strncmp(buf, "firejail-default", 16) == 0)
arg_apparmor = 1;
}
EUID_ROOT();
}
return;
errexit:
fprintf(stderr, "Error: cannot read /proc file\n");
exit(1);
}
#endif // HAVE_APPARMOR
static void extract_x11_display(pid_t pid) {
char *fname;
if (asprintf(&fname, "%s/%d", RUN_FIREJAIL_X11_DIR, pid) == -1)
errExit("asprintf");
FILE *fp = fopen(fname, "r");
free(fname);
if (!fp)
return;
if (1 != fscanf(fp, "%u", &display)) {
fprintf(stderr, "Error: cannot read X11 display file\n");
fclose(fp);
return;
}
fclose(fp);
// check display range
if (display < X11_DISPLAY_START || display > X11_DISPLAY_END) {
fprintf(stderr, "Error: invalid X11 display range\n");
return;
}
// store the display number for join process in /run/firejail/x11
EUID_ROOT();
set_x11_run_file(getpid(), display);
EUID_USER();
}
static void extract_command(int argc, char **argv, int index) {
EUID_ASSERT();
if (index >= argc)
return;
// doubledash followed by positional parameters
if (strcmp(argv[index], "--") == 0) {
arg_doubledash = 1;
index++;
if (index >= argc)
return;
}
// first argv needs to be a valid command
if (arg_doubledash == 0 && *argv[index] == '-') {
fprintf(stderr, "Error: invalid option %s after --join\n", argv[index]);
exit(1);
}
// build command
build_cmdline(&cfg.command_line, &cfg.window_title, argc, argv, index);
}
static void extract_nogroups(pid_t pid) {
char *fname;
if (asprintf(&fname, "/proc/%d/root%s", pid, RUN_GROUPS_CFG) == -1)
errExit("asprintf");
struct stat s;
if (stat(fname, &s) == -1) {
free(fname);
return;
}
arg_nogroups = 1;
free(fname);
}
static void extract_nonewprivs(pid_t pid) {
char *fname;
if (asprintf(&fname, "/proc/%d/root%s", pid, RUN_NONEWPRIVS_CFG) == -1)
errExit("asprintf");
struct stat s;
if (stat(fname, &s) == -1) {
free(fname);
return;
}
arg_nonewprivs = 1;
free(fname);
}
static void extract_cpu(pid_t pid) {
char *fname;
if (asprintf(&fname, "/proc/%d/root%s", pid, RUN_CPU_CFG) == -1)
errExit("asprintf");
struct stat s;
if (stat(fname, &s) == -1) {
free(fname);
return;
}
// there is a CPU_CFG file, load it!
load_cpu(fname);
free(fname);
}
static void extract_cgroup(pid_t pid) {
char *fname;
if (asprintf(&fname, "/proc/%d/root%s", pid, RUN_CGROUP_CFG) == -1)
errExit("asprintf");
struct stat s;
if (stat(fname, &s) == -1) {
free(fname);
return;
}
// there is a cgroup file CGROUP_CFG, load it!
load_cgroup(fname);
free(fname);
}
static void extract_caps(pid_t pid) {
// open stat file
char *file;
if (asprintf(&file, "/proc/%u/status", pid) == -1) {
perror("asprintf");
exit(1);
}
FILE *fp = fopen(file, "r");
if (!fp)
goto errexit;
char buf[BUFLEN];
while (fgets(buf, BUFLEN - 1, fp)) {
if (strncmp(buf, "CapBnd:", 7) == 0) {
char *ptr = buf + 7;
unsigned long long val;
if (sscanf(ptr, "%llx", &val) != 1)
goto errexit;
apply_caps = 1;
caps = val;
}
else if (strncmp(buf, "NoNewPrivs:", 11) == 0) {
char *ptr = buf + 11;
int val;
if (sscanf(ptr, "%d", &val) != 1)
goto errexit;
if (val)
arg_nonewprivs = 1;
}
}
fclose(fp);
free(file);
return;
errexit:
fprintf(stderr, "Error: cannot read stat file for process %u\n", pid);
exit(1);
}
static void extract_user_namespace(pid_t pid) {
// test user namespaces available in the kernel
struct stat s1;
struct stat s2;
struct stat s3;
if (stat("/proc/self/ns/user", &s1) == 0 &&
stat("/proc/self/uid_map", &s2) == 0 &&
stat("/proc/self/gid_map", &s3) == 0);
else
return;
// read uid map
char *uidmap;
if (asprintf(&uidmap, "/proc/%u/uid_map", pid) == -1)
errExit("asprintf");
FILE *fp = fopen(uidmap, "r");
if (!fp) {
free(uidmap);
return;
}
// check uid map
int u1;
int u2;
if (fscanf(fp, "%d %d", &u1, &u2) == 2) {
if (arg_debug)
printf("User namespace detected: %s, %d, %d\n", uidmap, u1, u2);
if (u1 != 0 || u2 != 0)
arg_noroot = 1;
}
fclose(fp);
free(uidmap);
}
static void extract_umask(pid_t pid) {
char *fname;
if (asprintf(&fname, "/proc/%d/root%s", pid, RUN_UMASK_FILE) == -1)
errExit("asprintf");
FILE *fp = fopen(fname, "re");
free(fname);
if (!fp) {
fprintf(stderr, "Error: cannot open umask file\n");
exit(1);
}
if (fscanf(fp, "%3o", &orig_umask) != 1) {
fprintf(stderr, "Error: cannot read umask\n");
exit(1);
}
fclose(fp);
}
static int open_shell(void) {
EUID_ASSERT();
assert(cfg.shell);
if (arg_debug)
printf("Opening shell %s\n", cfg.shell);
// file descriptor will leak if not opened with O_CLOEXEC !!
int fd = open(cfg.shell, O_PATH|O_CLOEXEC);
if (fd == -1) {
fprintf(stderr, "Error: cannot open shell %s\n", cfg.shell);
exit(1);
}
return fd;
}
// return false if the sandbox identified by pid is not fully set up yet or if
// it is no firejail sandbox at all, return true if the sandbox is complete
bool is_ready_for_join(const pid_t pid) {
EUID_ASSERT();
// check if a file /run/firejail/mnt/join exists
char *fname;
if (asprintf(&fname, "/proc/%d/root%s", pid, RUN_JOIN_FILE) == -1)
errExit("asprintf");
EUID_ROOT();
int fd = open(fname, O_RDONLY|O_CLOEXEC);
EUID_USER();
free(fname);
if (fd == -1)
return false;
struct stat s;
if (fstat(fd, &s) == -1)
errExit("fstat");
if (!S_ISREG(s.st_mode) || s.st_uid != 0 || s.st_size != 1) {
close(fd);
return false;
}
char status;
if (read(fd, &status, 1) == 1 && status == SANDBOX_DONE) {
close(fd);
return true;
}
close(fd);
return false;
}
#define SNOOZE 10000 // sleep interval in microseconds
void check_join_permission(pid_t pid) {
// check if pid belongs to a fully set up firejail sandbox
unsigned long i;
for (i = SNOOZE; is_ready_for_join(pid) == false; i += SNOOZE) { // give sandbox some time to start up
if (i > join_timeout) {
fprintf(stderr, "Error: no valid sandbox\n");
exit(1);
}
usleep(SNOOZE);
}
// check privileges for non-root users
uid_t uid = getuid();
if (uid != 0) {
uid_t sandbox_uid = pid_get_uid(pid);
if (uid != sandbox_uid) {
fprintf(stderr, "Error: permission is denied to join a sandbox created by a different user.\n");
exit(1);
}
}
}
pid_t switch_to_child(pid_t pid) {
EUID_ASSERT();
EUID_ROOT();
pid_t rv = pid;
errno = 0;
char *comm = pid_proc_comm(pid);
if (!comm) {
if (errno == ENOENT)
fprintf(stderr, "Error: cannot find process with pid %d\n", pid);
else
fprintf(stderr, "Error: cannot read /proc file\n");
exit(1);
}
EUID_USER();
if (strcmp(comm, "firejail") == 0) {
if (find_child(pid, &rv) == 1) {
fprintf(stderr, "Error: no valid sandbox\n");
exit(1);
}
fmessage("Switching to pid %u, the first child process inside the sandbox\n", (unsigned) rv);
}
free(comm);
return rv;
}
void join(pid_t pid, int argc, char **argv, int index) {
EUID_ASSERT();
pid_t parent = pid;
// in case the pid is that of a firejail process, use the pid of the first child process
pid = switch_to_child(pid);
// exit if no permission to join the sandbox
check_join_permission(pid);
extract_x11_display(parent);
int shfd = -1;
if (!arg_shell_none && !arg_audit)
shfd = open_shell();
EUID_ROOT();
// in user mode set caps seccomp, cpu, cgroup, etc
if (getuid() != 0) {
extract_nonewprivs(pid); // redundant on Linux >= 4.10; duplicated in function extract_caps
extract_caps(pid);
extract_cpu(pid);
extract_cgroup(pid);
extract_nogroups(pid);
extract_user_namespace(pid);
extract_umask(pid);
#ifdef HAVE_APPARMOR
extract_apparmor(pid);
#endif
}
// set cgroup
if (cfg.cgroup) // not available for uid 0
set_cgroup(cfg.cgroup);
// join namespaces
if (arg_join_network) {
if (join_namespace(pid, "net"))
exit(1);
}
else if (arg_join_filesystem) {
if (join_namespace(pid, "mnt"))
exit(1);
}
else {
if (join_namespace(pid, "ipc") ||
join_namespace(pid, "net") ||
join_namespace(pid, "pid") ||
join_namespace(pid, "uts") ||
join_namespace(pid, "mnt"))
exit(1);
}
pid_t child = fork();
if (child < 0)
errExit("fork");
if (child == 0) {
// drop discretionary access control capabilities for root sandboxes
caps_drop_dac_override();
// chroot into /proc/PID/root directory
char *rootdir;
if (asprintf(&rootdir, "/proc/%d/root", pid) == -1)
errExit("asprintf");
int rv;
if (!arg_join_network) {
rv = chroot(rootdir); // this will fail for processes in sandboxes not started with --chroot option
if (rv == 0)
printf("changing root to %s\n", rootdir);
}
EUID_USER();
if (chdir("/") < 0)
errExit("chdir");
if (cfg.homedir) {
struct stat s;
if (stat(cfg.homedir, &s) == 0) {
/* coverity[toctou] */
if (chdir(cfg.homedir) < 0)
errExit("chdir");
}
}
// set caps filter
EUID_ROOT();
if (apply_caps == 1) // not available for uid 0
caps_set(caps);
if (getuid() != 0)
seccomp_load_file_list();
// mount user namespace or drop privileges
if (arg_noroot) { // not available for uid 0
if (arg_debug)
printf("Joining user namespace\n");
if (join_namespace(1, "user"))
exit(1);
// user namespace resets capabilities
// set caps filter
if (apply_caps == 1) // not available for uid 0
caps_set(caps);
}
// set nonewprivs
if (arg_nonewprivs == 1) { // not available for uid 0
int rv = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
if (arg_debug && rv == 0)
printf("NO_NEW_PRIVS set\n");
}
EUID_USER();
int cwd = 0;
if (cfg.cwd) {
if (chdir(cfg.cwd) == 0)
cwd = 1;
}
if (!cwd) {
if (chdir("/") < 0)
errExit("chdir");
if (cfg.homedir) {
struct stat s;
if (stat(cfg.homedir, &s) == 0) {
/* coverity[toctou] */
if (chdir(cfg.homedir) < 0)
errExit("chdir");
}
}
}
// drop privileges
drop_privs(arg_nogroups);
// kill the child in case the parent died
prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
#ifdef HAVE_APPARMOR
// add apparmor confinement after the execve
set_apparmor();
#endif
extract_command(argc, argv, index);
if (cfg.command_line == NULL) {
assert(cfg.shell);
cfg.window_title = cfg.shell;
}
else if (arg_debug)
printf("Extracted command #%s#\n", cfg.command_line);
// set cpu affinity
if (cfg.cpus) // not available for uid 0
set_cpu_affinity();
// set nice value
if (arg_nice)
set_nice(cfg.nice);
// add x11 display
if (display) {
char *display_str;
if (asprintf(&display_str, ":%d", display) == -1)
errExit("asprintf");
env_store_name_val("DISPLAY", display_str, SETENV);
free(display_str);
}
#ifdef HAVE_DBUSPROXY
// set D-Bus environment variables
struct stat s;
if (stat(RUN_DBUS_USER_SOCKET, &s) == 0)
dbus_set_session_bus_env();
if (stat(RUN_DBUS_SYSTEM_SOCKET, &s) == 0)
dbus_set_system_bus_env();
#endif
start_application(0, shfd, NULL);
__builtin_unreachable();
}
EUID_USER();
if (shfd != -1)
close(shfd);
int status = 0;
//*****************************
// following code is signal-safe
install_handler();
// wait for the child to finish
waitpid(child, &status, 0);
// restore default signal action
signal(SIGTERM, SIG_DFL);
// end of signal-safe code
//*****************************
flush_stdin();
if (WIFEXITED(status)) {
status = WEXITSTATUS(status);
} else if (WIFSIGNALED(status)) {
status = WTERMSIG(status);
} else {
status = 0;
}
exit(status);
}
|