Messages in this thread Patch in this message | | | Date | Mon, 7 Jun 2010 20:08:55 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH v3 06/11] rlimits: do security check under task_lock |
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(add selinux maintainers)
First of all, my apologies for the huge delay. And I still didn't read the whole series, sorry.
On 06/06, Jiri Slaby wrote: > > +static int check_security_task_setrlimit_unlocked(struct task_struct *tsk, > + unsigned int resource, struct rlimit *new_rlim, > + struct rlimit *old_rlim) > +{ > + struct rlimit rlim; > + int ret; > + > + memcpy(&rlim, old_rlim, sizeof(rlim)); > + > + task_unlock(tsk->group_leader); > + ret = security_task_setrlimit(tsk, resource, new_rlim); > + task_lock(tsk->group_leader); > + > + if (!ret && memcmp(&rlim, old_rlim, sizeof(rlim))) > + return -EAGAIN; > + return ret; > +} > + > /* make sure you are allowed to change @tsk limits before calling this */ > int do_prlimit(struct task_struct *tsk, unsigned int resource, > struct rlimit *new_rlim, struct rlimit *old_rlim) > { > struct rlimit *rlim; > - int retval = 0; > + int retval; > > if (resource >= RLIM_NLIMITS) > return -EINVAL; > @@ -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)) > retval = -EPERM; > - if (!retval) > - retval = security_task_setrlimit(tsk, resource, > - new_rlim); > + if (!retval) { > + retval = check_security_task_setrlimit_unlocked(tsk, > + resource, new_rlim, rlim); > + if (retval == -EAGAIN) { > + goto again; > + } > + }
Oh. Can't we just ignore this (imho minor) race ? Or just verify/document that current_has_perm() can be called under task_lock. Actually, I do not think we have a race, selinux_task_setrlimit() only checks that the caller has rights to change the rlimits.
And. Given that avc_has_perm() can be called from irq context (say, selinux_file_send_sigiotask or selinux_task_kill), we can assume it is safe to call it under task_lock() which is not irq-safe.
But. OTOH, if we are really worried about security_ ops, then we have another reason to call this hook under task_lock(), and we probably want to modify selinux_bprm_committing_creds() to take this lock too:
--- security/selinux/hooks.c +++ security/selinux/hooks.c @@ -2333,11 +2333,14 @@ static void selinux_bprm_committing_cred rc = avc_has_perm(new_tsec->osid, new_tsec->sid, SECCLASS_PROCESS, PROCESS__RLIMITINH, NULL); if (rc) { + /* protects against do_prlimit() */ + task_lock(current); for (i = 0; i < RLIM_NLIMITS; i++) { rlim = current->signal->rlim + i; initrlim = init_task.signal->rlim + i; rlim->rlim_cur = min(rlim->rlim_max, initrlim->rlim_cur); } + task_unlock(current); update_rlimit_cpu(current->signal->rlim[RLIMIT_CPU].rlim_cur); } }
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.
Perhaps it makes sense to do selinux_task_setrlimit(p->group_leader)? At least in this case the result should be "consistent".
Oleg.
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