Forbid fd_advise on directories (#240)

* Forbid fd_advise on directories

This commit adds a check to `fd_advise`.  If the fd is a directory,
return `ebadf`.  This brings uvwasi in line with Wasmtime's behavior.
WASI folks have stated that fd_advise should not work on directories
as this is a Linux-specific behavior.

src/uvwasi.c

@@ -8,6 +8,8 @@
 # include <dirent.h>
 # include <time.h>
 #else
+# define _CRT_INTERNAL_NONSTDC_NAMES 1
+# include <sys/stat.h>
 # include <io.h>
 #endif /* _WIN32 */
 
@@ -17,6 +19,10 @@
 # define UVWASI_FD_READDIR_SUPPORTED 1
 #endif
 
+#if !defined(S_ISDIR) && defined(S_IFMT) && defined(S_IFDIR)
+  #define S_ISDIR(m) (((m) & S_IFMT) == S_IFDIR)
+#endif
+
 #include "uvwasi.h"
 #include "uvwasi_alloc.h"
 #include "uv.h"
@@ -627,9 +633,10 @@ uvwasi_errno_t uvwasi_fd_advise(uvwasi_t* uvwasi,
                                 uvwasi_advice_t advice) {
   struct uvwasi_fd_wrap_t* wrap;
   uvwasi_errno_t err;
+  uv_fs_t req;
+  int r;
 #ifdef POSIX_FADV_NORMAL
   int mapped_advice;
-  int r;
 #endif /* POSIX_FADV_NORMAL */
 
   UVWASI_DEBUG("uvwasi_fd_advise(uvwasi=%p, fd=%d, offset=%"PRIu64", "
@@ -682,14 +689,27 @@ uvwasi_errno_t uvwasi_fd_advise(uvwasi_t* uvwasi,
   if (err != UVWASI_ESUCCESS)
     return err;
 
+  r = uv_fs_fstat(NULL, &req, wrap->fd, NULL);
+  if (r == -1) {
+    err = uvwasi__translate_uv_error(r);
+    goto exit;
+  }
+
+  if (S_ISDIR(req.statbuf.st_mode)) {
+    err = UVWASI_EBADF;
+    goto exit;
+  }
+
   err = UVWASI_ESUCCESS;
 
 #ifdef POSIX_FADV_NORMAL
   r = posix_fadvise(wrap->fd, offset, len, mapped_advice);
   if (r != 0)
     err = uvwasi__translate_uv_error(uv_translate_sys_error(r));
 #endif /* POSIX_FADV_NORMAL */
+exit:
   uv_mutex_unlock(&wrap->mutex);
+  uv_fs_req_cleanup(&req);
   return err;
 }
 

test/test-fd-advise-dir.c

@@ -0,0 +1,45 @@
+#include <assert.h>
+#include <stdlib.h>
+
+#include "uv.h"
+#include "uvwasi.h"
+#include "test-common.h"
+
+#define TEST_TMP_DIR "./out/tmp"
+#define TEST_PATH_ADVISE TEST_TMP_DIR "/test_fd_advise_dir"
+
+int main(void) {
+#if !defined(_WIN32) && !defined(__ANDROID__)
+  uvwasi_t uvwasi;
+  uvwasi_options_t init_options;
+  uv_fs_t req;
+  uvwasi_errno_t err;
+  int r;
+
+  setup_test_environment();
+
+  r = uv_fs_mkdir(NULL, &req, TEST_TMP_DIR, 0777, NULL);
+  uv_fs_req_cleanup(&req);
+  assert(r == 0 || r == UV_EEXIST);
+
+  r = uv_fs_mkdir(NULL, &req, TEST_PATH_ADVISE, 0777, NULL);
+  uv_fs_req_cleanup(&req);
+  assert(r == 0 || r == UV_EEXIST);
+
+  uvwasi_options_init(&init_options);
+  init_options.preopenc = 1;
+  init_options.preopens = calloc(1, sizeof(uvwasi_preopen_t));
+  init_options.preopens[0].mapped_path = "/var";
+  init_options.preopens[0].real_path = TEST_PATH_ADVISE;
+
+  err = uvwasi_init(&uvwasi, &init_options);
+  assert(err == 0);
+
+  err = uvwasi_fd_advise(&uvwasi, 3, 10, 20, UVWASI_ADVICE_DONTNEED);
+  assert(err == UVWASI_EBADF);
+
+  uvwasi_destroy(&uvwasi);
+  free(init_options.preopens);
+#endif /* !defined(_WIN32) && !defined(__ANDROID__) */
+  return 0;
+}