1 // SPDX-License-Identifier: GPL-2.0
2 
3 #define _GNU_SOURCE
4 #include <errno.h>
5 #include <fcntl.h>
6 #include <sched.h>
7 #include <stdio.h>
8 #include <stdlib.h>
9 #include <string.h>
10 #include <sys/ioctl.h>
11 #include <sys/mount.h>
12 #include <sys/stat.h>
13 #include <sys/types.h>
14 #include <unistd.h>
15 #include <linux/android/binder.h>
16 #include <linux/android/binderfs.h>
17 
main(int argc,char * argv[])18 int main(int argc, char *argv[])
19 {
20 	int fd, ret, saved_errno;
21 	struct binderfs_device device = { 0 };
22 
23 	ret = unshare(CLONE_NEWNS);
24 	if (ret < 0) {
25 		fprintf(stderr, "%s - Failed to unshare mount namespace\n",
26 			strerror(errno));
27 		exit(EXIT_FAILURE);
28 	}
29 
30 	ret = mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, 0);
31 	if (ret < 0) {
32 		fprintf(stderr, "%s - Failed to mount / as private\n",
33 			strerror(errno));
34 		exit(EXIT_FAILURE);
35 	}
36 
37 	ret = mkdir("/dev/binderfs", 0755);
38 	if (ret < 0 && errno != EEXIST) {
39 		fprintf(stderr, "%s - Failed to create binderfs mountpoint\n",
40 			strerror(errno));
41 		exit(EXIT_FAILURE);
42 	}
43 
44 	ret = mount(NULL, "/dev/binderfs", "binder", 0, 0);
45 	if (ret < 0) {
46 		fprintf(stderr, "%s - Failed to mount binderfs\n",
47 			strerror(errno));
48 		exit(EXIT_FAILURE);
49 	}
50 
51 	memcpy(device.name, "my-binder", strlen("my-binder"));
52 
53 	fd = open("/dev/binderfs/binder-control", O_RDONLY | O_CLOEXEC);
54 	if (fd < 0) {
55 		fprintf(stderr, "%s - Failed to open binder-control device\n",
56 			strerror(errno));
57 		exit(EXIT_FAILURE);
58 	}
59 
60 	ret = ioctl(fd, BINDER_CTL_ADD, &device);
61 	saved_errno = errno;
62 	close(fd);
63 	errno = saved_errno;
64 	if (ret < 0) {
65 		fprintf(stderr, "%s - Failed to allocate new binder device\n",
66 			strerror(errno));
67 		exit(EXIT_FAILURE);
68 	}
69 
70 	printf("Allocated new binder device with major %d, minor %d, and name %s\n",
71 	       device.major, device.minor, device.name);
72 
73 	ret = unlink("/dev/binderfs/my-binder");
74 	if (ret < 0) {
75 		fprintf(stderr, "%s - Failed to delete binder device\n",
76 			strerror(errno));
77 		exit(EXIT_FAILURE);
78 	}
79 
80 	/* Cleanup happens when the mount namespace dies. */
81 	exit(EXIT_SUCCESS);
82 }
83