1#include <unistd.h>
 2#include <fcntl.h>
 3#include <sys/wait.h>
 4#include "syscall.h"
 5#include "pthread_impl.h"
 6
 7struct ctx {
 8	int fd;
 9	const char *filename;
10	int amode;
11	int p;
12};
13
14static int checker(void *p)
15{
16	struct ctx *c = p;
17	int ret;
18	if (__syscall(SYS_setregid, __syscall(SYS_getegid), -1)
19	    || __syscall(SYS_setreuid, __syscall(SYS_geteuid), -1))
20		__syscall(SYS_exit, 1);
21	ret = __syscall(SYS_faccessat, c->fd, c->filename, c->amode, 0);
22	__syscall(SYS_write, c->p, &ret, sizeof ret);
23	return 0;
24}
25
26int faccessat(int fd, const char *filename, int amode, int flag)
27{
28	if (flag) {
29		int ret = __syscall(SYS_faccessat2, fd, filename, amode, flag);
30		if (ret != -ENOSYS) return __syscall_ret(ret);
31	}
32
33	if (flag & ~AT_EACCESS)
34		return __syscall_ret(-EINVAL);
35
36	if (!flag || (getuid()==geteuid() && getgid()==getegid()))
37		return syscall(SYS_faccessat, fd, filename, amode);
38
39	char stack[1024];
40	sigset_t set;
41	pid_t pid;
42	int status;
43	int ret, p[2];
44
45	if (pipe2(p, O_CLOEXEC)) return __syscall_ret(-EBUSY);
46	struct ctx c = { .fd = fd, .filename = filename, .amode = amode, .p = p[1] };
47
48	__block_all_sigs(&set);
49	
50	pid = __clone(checker, stack+sizeof stack, 0, &c);
51	__syscall(SYS_close, p[1]);
52
53	if (pid<0 || __syscall(SYS_read, p[0], &ret, sizeof ret) != sizeof(ret))
54		ret = -EBUSY;
55	__syscall(SYS_close, p[0]);
56	__sys_wait4(pid, &status, __WCLONE, 0);
57
58	__restore_sigs(&set);
59
60	return __syscall_ret(ret);
61}