src/unistd/faccessat.c

   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 }