client: disallow unprivileged users to escalate root privileges

client: disallow unprivileged users to escalate root privileges

Origin: https://github.com/ceph/ceph/commit/b6d85b595ea7c9e0fca10d5e77a48102110fe22c
Bug-Debian: https://bugs.debian.org/1108410
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2025-52555

An unprivileged user can `chmod 777` a directory owned by root
and gain access. Fix this bug and also add a test case for the
same.

Signed-off-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Venky Shankar <vshankar@redhat.com>
Gbp-Pq: Name client-disallow-unprivileged-users-to-escalate-root-.patch