unix: squelch fchmod() EPERM on CIFS share

uv_fs_copyfile() calls fchmod() to change the target file's permissions
to the source file's permissions but that operation errors with EPERM on
CIFS shares unless they are mounted with the "noperm" option.

Since UNIX-style permissions don't make sense for CIFS anyway, let's
handle the error in libuv by recognizing that it's a CIFS share and
continuing when that is the case.

The same logic probably applies to (a subset of) FUSE file systems but
those haven't been whitelisted yet.

Fixes: libuv#2596
Refs: nodejs/node#31170

src/unix/fs.c

@@ -1137,7 +1137,28 @@ static ssize_t uv__fs_copyfile(uv_fs_t* req) {
 
   if (fchmod(dstfd, src_statsbuf.st_mode) == -1) {
     err = UV__ERR(errno);
+#ifdef __linux__
+    if (err != UV_EPERM)
+      goto out;
+
+    {
+      struct statfs s;
+
+      /* fchmod() on CIFS shares always fails with EPERM unless the share is
+       * mounted with "noperm". As fchmod() is a meaningless operation on such
+       * shares anyway, detect that condition and squelch the error.
+       */
+      if (fstatfs(dstfd, &s) == -1)
+        goto out;
+
+      if (s.f_type != /* CIFS */ 0xFF534D42u)
+        goto out;
+    }
+
+    err = 0;
+#else  /* !__linux__ */
     goto out;
+#endif  /* !__linux__ */
   }
 
 #ifdef FICLONE