On Sat, Jun 27, 2020 at 9:23 AM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote:
>
> Require the target task to be a descendant of the container
> orchestrator/engine.
>
> You would only change the audit container ID from one set or inherited
> value to another if you were nesting containers.
>
> If changing the contid, the container orchestrator/engine must be a
> descendant and not same orchestrator as the one that set it so it is not
> possible to change the contid of another orchestrator's container.
>
> Since the task_is_descendant() function is used in YAMA and in audit,
> remove the duplication and pull the function into kernel/core/sched.c
>
> Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
> ---
> include/linux/sched.h | 3 +++
> kernel/audit.c | 23 +++++++++++++++++++++--
> kernel/sched/core.c | 33 +++++++++++++++++++++++++++++++++
> security/yama/yama_lsm.c | 33 ---------------------------------
> 4 files changed, 57 insertions(+), 35 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 2213ac670386..06938d0b9e0c 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2047,4 +2047,7 @@ static inline void rseq_syscall(struct pt_regs *regs)
>
> const struct cpumask *sched_trace_rd_span(struct root_domain *rd);
>
> +extern int task_is_descendant(struct task_struct *parent,
> + struct task_struct *child);
> +
> #endif
> diff --git a/kernel/audit.c b/kernel/audit.c
> index a862721dfd9b..efa65ec01239 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -2713,6 +2713,20 @@ int audit_signal_info(int sig, struct task_struct *t)
> return audit_signal_info_syscall(t);
> }
>
> +static bool audit_contid_isnesting(struct task_struct *tsk)
> +{
> + bool isowner = false;
> + bool ownerisparent = false;
> +
> + rcu_read_lock();
> + if (tsk->audit && tsk->audit->cont) {
> + isowner = current == tsk->audit->cont->owner;
> + ownerisparent = task_is_descendant(tsk->audit->cont->owner, current);
I want to make sure I'm understanding this correctly and I keep
mentally tripping over something: it seems like for a given audit
container ID a task is either the owner or a descendent, there is no
third state, is that correct?
Assuming that is true, can the descendent check simply be a negative
owner check given they both have the same audit container ID?
> + }
> + rcu_read_unlock();
> + return !isowner && ownerisparent;
> +}
> +
> /*
> * audit_set_contid - set current task's audit contid
> * @task: target task
> @@ -2755,8 +2769,13 @@ int audit_set_contid(struct task_struct *task, u64 contid)
> rc = -EBUSY;
> goto unlock;
> }
> - /* if contid is already set, deny */
> - if (audit_contid_set(task))
> + /* if task is not descendant, block */
> + if (task == current || !task_is_descendant(current, task)) {
I'm also still fuzzy on why we can't let a task set it's own audit
container ID, assuming it meets all the criteria established in patch
2/13. It somewhat made sense when you were tracking inherited vs
explicitly set audit container IDs, but that doesn't appear to be the
case so far in this patchset, yes?
> + rc = -EXDEV;
I'm fairly confident we had a discussion about not using all these
different error codes, but that may be a moot point given my next
comment.
> + goto unlock;
> + }
> + /* only allow contid setting again if nesting */
> + if (audit_contid_set(task) && !audit_contid_isnesting(task))
> rc = -EEXIST;
It seems like what we need in audit_set_contid() is a check to ensure
that the task being modified is only modified by the owner of the
audit container ID, yes? If so, I would think we could do this quite
easily with the following, or similar logic, (NOTE: assumes both
current and tsk are properly setup):
if ((current->audit->cont != tsk->audit->cont) ||
(current->audit->cont->owner != current))
return -EACCESS;
This is somewhat independent of the above issue, but we may also want
to add to the capability check. Patch 2 adds a
"capable(CAP_AUDIT_CONTROL)" which is good, but perhaps we also need a
"ns_capable(CAP_AUDIT_CONTROL)" to allow a given audit container ID
orchestrator/owner the ability to control which of it's descendants
can change their audit container ID, for example:
if (!capable(CAP_AUDIT_CONTROL) ||
!ns_capable(current->nsproxy->user_ns, CAP_AUDIT_CONTROL))
return -EPERM;
--
paul moore
www.paul-moore.com
