github.com/afumu/libc@v0.0.6/musl/src/unistd/faccessat.c (about)

     1  #include <unistd.h>
     2  #include <fcntl.h>
     3  #include <sys/wait.h>
     4  #include "syscall.h"
     5  #include "pthread_impl.h"
     6  
     7  struct ctx {
     8  	int fd;
     9  	const char *filename;
    10  	int amode;
    11  	int p;
    12  };
    13  
    14  static 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  
    26  int faccessat(int fd, const char *filename, int amode, int flag)
    27  {
    28  	if (!flag || (flag==AT_EACCESS && getuid()==geteuid() && getgid()==getegid()))
    29  		return syscall(SYS_faccessat, fd, filename, amode, flag);
    30  
    31  	if (flag != AT_EACCESS)
    32  		return __syscall_ret(-EINVAL);
    33  
    34  	char stack[1024];
    35  	sigset_t set;
    36  	pid_t pid;
    37  	int status;
    38  	int ret, p[2];
    39  
    40  	if (pipe2(p, O_CLOEXEC)) return __syscall_ret(-EBUSY);
    41  	struct ctx c = { .fd = fd, .filename = filename, .amode = amode, .p = p[1] };
    42  
    43  	__block_all_sigs(&set);
    44  	
    45  	pid = __clone(checker, stack+sizeof stack, 0, &c);
    46  	__syscall(SYS_close, p[1]);
    47  
    48  	if (pid<0 || __syscall(SYS_read, p[0], &ret, sizeof ret) != sizeof(ret))
    49  		ret = -EBUSY;
    50  	__syscall(SYS_close, p[0]);
    51  	__syscall(SYS_wait4, pid, &status, __WCLONE, 0);
    52  
    53  	__restore_sigs(&set);
    54  
    55  	return __syscall_ret(ret);
    56  }