[PATCH v4 1/5] userns: record how far up CAP_SETFCAP reaches

[sashiko-bot at kernel.org]

> create_user_ns() records in ns->parent_could_setfcap whether the creator
> had CAP_SETFCAP in its effective set, and verify_root_map() trusts that
> when a task in the new namespace maps the parent's uid 0.  A bool only
> describes the parent, though.  File capabilities belong to the kuid of a
> root user, and a namespace that maps the parent's uid 0 shares that kuid
> with the parent and possibly with ancestors further up, so what matters
> is how far up the creator's CAP_SETFCAP counted.
> 
> Replace the bool with ns->setfcap_level: CAP_SETFCAP held in the
> namespace counts there and in its ancestors up to the one at that
> ->level.  cap_setfcap_level() computes it from the creator's cred.  A
> creator that holds CAP_SETFCAP passes on the setfcap_level of its own
> namespace, one that doesn't gets the new namespace's own level, and the
> initial namespace has 0.
> 
> verify_root_map() keeps checking the same condition: the bool was false
> exactly when the level is the namespace's own.
> 
> No functional change.
> 
> Reviewed-by: Bradley Morgan <brads at mainlining.org>
> Assisted-by: LLM
> Signed-off-by: Josef Bacik <josef at toxicpanda.com>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261022-b4-setfcap-userns-v4-0-88aa0ffaa08f@toxicpanda.com?part=1