One of the last remaining users of strlcpy() in the kernel is
kernfs_path_from_node_locked(), which passes back the problematic "length
we _would_ have copied" return value to indicate truncation.  Convert the
chain of all callers to use the negative return value (some of which
already doing this explicitly). All callers were already also checking
for negative return values, so the risk to missed checks looks very low.

In this analysis, it was found that cgroup1_release_agent() actually
didn't handle the "too large" condition, so this is technically also a
bug fix. :)

Here's the chain of callers, and resolution identifying each one as now
handling the correct return value:

kernfs_path_from_node_locked()
        kernfs_path_from_node()
                pr_cont_kernfs_path()
                        returns void
                kernfs_path()
                        sysfs_warn_dup()
                                return value ignored
                        cgroup_path()
                                blkg_path()
                                        bfq_bic_update_cgroup()
                                                return value ignored
                                TRACE_IOCG_PATH()
                                        return value ignored
                                TRACE_CGROUP_PATH()
                                        return value ignored
                                perf_event_cgroup()
                                        return value ignored
                                task_group_path()
                                        return value ignored
                                damon_sysfs_memcg_path_eq()
                                        return value ignored
                                get_mm_memcg_path()
                                        return value ignored
                                lru_gen_seq_show()
                                        return value ignored
                        cgroup_path_from_kernfs_id()
                                return value ignored
                cgroup_show_path()
                        already converted "too large" error to negative value
                cgroup_path_ns_locked()
                        cgroup_path_ns()
                                bpf_iter_cgroup_show_fdinfo()
                                        return value ignored
                                cgroup1_release_agent()
                                        wasn't checking "too large" error
                        proc_cgroup_show()
                                already converted "too large" to negative value

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Zefan Li <lizefan.x@bytedance.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Waiman Long <longman@redhat.com>
Cc:  <cgroups@vger.kernel.org>
Co-developed-by: Azeem Shaikh <azeemshaikh38@gmail.com>
Signed-off-by: Azeem Shaikh <azeemshaikh38@gmail.com>
Link: https://lore.kernel.org/r/20231116192127.1558276-3-keescook@chromium.orgSigned-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20231212211741.164376-3-keescook@chromium.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>