faccessat.c raw

   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) {
  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  	__syscall(SYS_wait4, pid, &status, __WCLONE, 0);
  57  
  58  	__restore_sigs(&set);
  59  
  60  	return __syscall_ret(ret);
  61  }
  62