Make improvements

- Invent openatemp() API
- Invent O_UNLINK open flag
- Introduce getenv_secure() API
- Remove `git pull` from cosmocc
- Fix utimes() when path is NULL
- Fix mktemp() to never return NULL
- Fix utimensat() UTIME_OMIT on XNU
- Improve utimensat() code for RHEL5
- Turn `argv[0]` C:/ to /C/ on Windows
- Introduce tmpnam() and tmpnam_r() APIs
- Fix more const issues with internal APIs
- Permit utimes() on WIN32 in O_RDONLY mode
- Fix fdopendir() to check fd is a directory
- Fix recent crash regression in landlock make
- Fix futimens(AT_FDCWD, NULL) to return EBADF
- Use workaround so `make -j` doesn't fork bomb
- Rename dontdiscard to __wur (just like glibc)
- Fix st_size for WIN32 symlinks containing UTF-8
- Introduce stdio ext APIs needed by GNU coreutils
- Fix lstat() on WIN32 for symlinks to directories
- Move some constants from normalize.inc to limits.h
- Fix segv with memchr() and memcmp() overlapping page
- Implement POSIX fflush() behavior for reader streams
- Implement AT_SYMLINK_NOFOLLOW for utimensat() on WIN32
- Don't change read-only status of existing files on WIN32
- Correctly handle `0x[^[:xdigit:]]` case in strtol() functions

libc/stdio/dirstream.c

@@ -21,6 +21,7 @@
 #include "libc/calls/internal.h"
 #include "libc/calls/struct/dirent.h"
 #include "libc/calls/struct/stat.h"
+#include "libc/calls/syscall-sysv.internal.h"
 #include "libc/calls/syscall_support-nt.internal.h"
 #include "libc/dce.h"
 #include "libc/errno.h"
@@ -42,6 +43,7 @@
 #include "libc/runtime/zipos.internal.h"
 #include "libc/str/str.h"
 #include "libc/sysv/consts/dt.h"
+#include "libc/sysv/consts/f.h"
 #include "libc/sysv/consts/o.h"
 #include "libc/sysv/consts/s.h"
 #include "libc/sysv/errfuns.h"
@@ -262,6 +264,20 @@ GiveUpOnGettingInode:
  */
 DIR *fdopendir(int fd) {
 
+  // sanity check file descriptor
+  struct stat st;
+  if (fstat(fd, &st) == -1) {
+    return 0;
+  }
+  if (!S_ISDIR(st.st_mode)) {
+    enotdir();
+    return 0;
+  }
+  if (IsLinux() && (__sys_fcntl(fd, F_GETFL) & O_PATH)) {
+    ebadf();
+    return 0;
+  }
+
   // allocate directory iterator object
   DIR *dir;
   if (!(dir = calloc(1, sizeof(*dir)))) {