Messages in this thread | | | Date | Wed, 23 Jun 2010 19:44:36 +0200 | From | Jiri Slaby <> | Subject | Re: [PATCH v3 06/11] rlimits: do security check under task_lock |
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On 06/23/2010 06:12 PM, Oleg Nesterov wrote: > On 06/23, Jiri Slaby wrote: >> >> On 06/07/2010 08:08 PM, Oleg Nesterov wrote: >>> On 06/06, Jiri Slaby wrote: >>>> @@ -1339,13 +1364,19 @@ int do_prlimit(struct task_struct *tsk, unsigned int resource, >>>> >>>> rlim = tsk->signal->rlim + resource; >>>> task_lock(tsk->group_leader); >>>> +again: >>>> + retval = 0; >>>> if (new_rlim) { >>>> if ((new_rlim->rlim_max > rlim->rlim_max) && >>>> !capable(CAP_SYS_RESOURCE)) >> >> BTW this capable() has the exactly same problem with being called with >> task_lock held. Is it OK to move it completely out of critical section? >> I'm asking because it sets a current->flags SU bit used for accounting. >> If I move it out of the section, it will set the bit always. > > Well, with all these delays I do not know what "exactly same problem" > means ;) Please explain?
As I wrote: that the capable() is called with task_lock held. With security enabled, capable() goes through all the avc_has_perm_noaudit, avc_audit and similar (in selinux), the same as security_task_setrlimit which we were writing about -- Andrew complaining about doing very long security checks while holding spinlocks.
I mean we should do either none of capable and selinux_task_setrlimit under task_lock or both :).
>>> Finally. selinux_task_setrlimit(p) uses __task_cred(p) for the check. >>> This looks a bit strange, different threads can have different creds >>> but obviously rlimits are per-process. >> >> Sorry I can't see it. Could you point out in which function this is done? > > selinux_task_setrlimit()->current_has_perm()->current_sid()->current_cred()
I still see no way how this is wrong. We want to check whether current thread has capabilities to change (someone else's) rlimits. Maybe I'm missing something?
thanks, -- js
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