Re: [PATCH ghak90 V8 04/16] audit: convert to contid list to check for orch/engine ownership

On 2020-01-22 16:28, Paul Moore wrote: > On Tue, Dec 31, 2019 at 2:50 PM Richard Guy Briggs <rgb(a)redhat.com&gt; wrote: > > > > Store the audit container identifier in a refcounted kernel object that > > is added to the master list of audit container identifiers. This will > > allow multiple container orchestrators/engines to work on the same > > machine without danger of inadvertantly re-using an existing identifier. > > It will also allow an orchestrator to inject a process into an existing > > container by checking if the original container owner is the one > > injecting the task. A hash table list is used to optimize searches. > > > > Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com&gt; > > --- > > include/linux/audit.h | 14 ++++++-- > > kernel/audit.c | 98 ++++++++++++++++++++++++++++++++++++++++++++++++--- > > kernel/audit.h | 8 +++++ > > 3 files changed, 112 insertions(+), 8 deletions(-)

> > @@ -232,7 +263,11 @@ int audit_alloc(struct task_struct *tsk) > > } > > info->loginuid = audit_get_loginuid(current); > > info->sessionid = audit_get_sessionid(current); > > - info->contid = audit_get_contid(current); > > + spin_lock(&audit_contobj_list_lock); > > + info->cont = _audit_contobj(current); > > + if (info->cont) > > + _audit_contobj_hold(info->cont); > > + spin_unlock(&audit_contobj_list_lock); > > If we are taking a spinlock in order to bump the refcount, does it > really need to be a refcount_t or can we just use a normal integer? > In RCU protected lists a spinlock is usually used to protect > adds/removes to the list, not the content of individual list items. > > My guess is you probably want to use the spinlock as described above > (list add/remove protection) and manipulate the refcount_t inside a > RCU read lock protected region. Ok, I guess it could be an integer if it were protected by the spinlock, but I think you've guessed my intent, so let us keep it as a refcount and tighten the spinlock scope and use rcu read locking to protect _get and _put in _alloc, _free, and later on when protecting the network namespace contobj lists. This should reduce potential contention for the spinlock to one location over fewer lines of code in that place while speeding up updates and slightly simplifying code in the others.

> > @@ -2381,9 +2425,12 @@ int audit_set_contid(struct task_struct *task, u64 contid) > > } > > oldcontid = audit_get_contid(task); > > read_lock(&tasklist_lock); > > - /* Don't allow the audit containerid to be unset */ > > + /* Don't allow the contid to be unset */ > > if (!audit_contid_valid(contid)) > > rc = -EINVAL; > > + /* Don't allow the contid to be set to the same value again */ > > + else if (contid == oldcontid) { > > + rc = -EADDRINUSE; > > First, is that brace a typo? It looks like it. Did this compile? Yes, it was fixed in the later patch that restructured the if statements.

> Second, can you explain why (re)setting the audit container ID to the > same value is something we need to prohibit? I'm guessing it has > something to do with explicitly set vs inherited, but I don't want to > assume too much about your thinking behind this. It made the refcounting more complicated later, and besides, the prohibition on setting the contid again if it is already set would catch this case, so I'll remove it in this patch and ensure this action doesn't cause a problem in later patches. > If it is "set vs inherited", would allowing an orchestrator to > explicitly "set" an inherited audit container ID provide some level or > protection against moving the task? I can't see it helping prevent this since later descendancy checks will stop this move anyways.

> > @@ -2396,8 +2443,49 @@ int audit_set_contid(struct task_struct *task, u64 contid) > > else if (audit_contid_set(task)) > > rc = -ECHILD; > > read_unlock(&tasklist_lock); > > - if (!rc) > > - task->audit->contid = contid; > > + if (!rc) { > > + struct audit_contobj *oldcont = _audit_contobj(task); > > + struct audit_contobj *cont = NULL, *newcont = NULL; > > + int h = audit_hash_contid(contid); > > + > > + rcu_read_lock(); > > + list_for_each_entry_rcu(cont, &audit_contid_hash[h], list) > > + if (cont->id == contid) { > > + /* task injection to existing container */ > > + if (current == cont->owner) { > > Do we have any protection against the task pointed to by cont->owner > going away and a new task with the same current pointer value (no > longer the legitimate audit container ID owner) manipulating the > target task's audit container ID? Yes, the get_task_struct() call below.