In hsr_newlink(), a provided but invalid IFLA_HSR_INTERLINK attribute was silently ignored if __dev_get_by_index() returned NULL. This leads to incorrect RedBox topology creation without notifying the user. Fix this by returning -EINVAL and an extack message when the interlink attribute is present but cannot be resolved. Reviewed-by: Felix Maurer <fmaurer@redhat.com> Signed-off-by: Luka Gejak <luka.gejak@linux.dev> Reviewed-by: Fernando Fernandez Mancera <fmancera@suse.de> Link: https://patch.msgid.link/20260513182657.20346-3-luka.gejak@linux.dev Signed-off-by: Jakub Kicinski <kuba@kernel.org>