[PATCH 1/8] lsm: always call the namespace_free hook

[sashiko-bot at kernel.org]

> security_namespace_free() returns early if ns->ns_security is NULL and
> skips the namespace_free hook. But ns->ns_security is only allocated if
> an LSM requests a namespace blob via lbs_ns and currently no LSM does.
> So the namespace_free hook is never called at all.
> 
> Landlock only uses namespace_init and namespace_install so it doesn't
> care. But the bpf LSM attaches to every hook and a program attached to
> namespace_free never runs. We want to use it in systemd-nsresourced to
> get notified when a user namespace goes away. Right now it has to kprobe
> retire_userns_sysctls() for that.
> 
> Note that a bpf program can't work around this. The size of the
> namespace blob is fixed at boot and the bpf LSM doesn't request one.
> And security_namespace_init() allocates the blob before the
> namespace_init hooks are called anyway.
> [ ... ]
>   after:  @init: 200 @free: 200
> 
> Fixes: f675d2e95569 ("lsm: add LSM blob and hooks for namespaces")
> Cc: <stable at kernel.org> # mainline only
> Signed-off-by: Christian Brauner (Amutable) <brauner at kernel.org>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261026-work-security-namespace_free-v1-0-ffa3ebbf71bd@kernel.org?part=1