Re: [PATCH 0/3] MR6855: server: Fix renaming file to a hardlink of itself.

[Jinoh Kang (＠iamahuman)]

Jinoh Kang (@iamahuman) commented about server/fd.c:
>  {
>      if (!fstat( fd->unix_fd, &st2 ) && st.st_ino == st2.st_ino && st.st_dev == st2.st_dev)
>      {
> -
>        if (create_link && !replace) set_error( STATUS_OBJECT_NAME_COLLISION );
> -
>        if (!create_link)
> -
>        {
> -
>            char src[PATH_MAX], dst[PATH_MAX];
> -
> -
>            /* if it's not the "same" file (by path), it means it's a hardlink, so remove the source */
> -
>            if (!realpath( fd->unix_name, src ) || !realpath( name, dst ) || (strcmp( src, dst ) && unlink( src )))

Instead of resolving the full realpath, we can check if:

1. their dirnames resolve to different dev/ino, which means they belong to a different directory, or
2. they have different basenames (even if they belong to the same directory).

Granted, there might be an edge case regarding symlinks and/or mount points, but I suspect the existing code isn't fully correct in this regard either, so I guess it's fine.