From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752469AbZBQLQP (ORCPT ); Tue, 17 Feb 2009 06:16:15 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751157AbZBQLP7 (ORCPT ); Tue, 17 Feb 2009 06:15:59 -0500 Received: from casper.infradead.org ([85.118.1.10]:42993 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751123AbZBQLP6 (ORCPT ); Tue, 17 Feb 2009 06:15:58 -0500 Subject: Re: RT scheduling and a way to make a process hang, unkillable From: Peter Zijlstra To: Dhaval Giani Cc: Corey Hickey , linux-kernel@vger.kernel.org, Bharata B Rao , Balbir Singh , Srivatsa Vaddagiri , Ingo Molnar , mtk.manpages@gmail.com, Alan Cox In-Reply-To: <20090217101542.GB15989@linux.vnet.ibm.com> References: <4997672B.1000301@fatooh.org> <1234697096.4713.24.camel@laptop> <20090216103636.GC17355@linux.vnet.ibm.com> <1234782516.4703.15.camel@laptop> <20090216120213.GB3925@linux.vnet.ibm.com> <1234787082.30178.3.camel@laptop> <20090216131440.GC3925@linux.vnet.ibm.com> <20090216132014.GD3925@linux.vnet.ibm.com> <4999BC0C.1010304@fatooh.org> <20090217050033.GA10409@linux.vnet.ibm.com> <20090217101542.GB15989@linux.vnet.ibm.com> Content-Type: text/plain Date: Tue, 17 Feb 2009 12:15:39 +0100 Message-Id: <1234869339.4744.77.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.25.90 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2009-02-17 at 15:45 +0530, Dhaval Giani wrote: > sched: Don't allow setuid to succeed if the user does not have rt bandwidth > > Corey Hickey reported that on using setuid to change the uid of a > rt process, the process would be unkillable and not be running. > This is because there was no rt runtime for that user group. Add > in a check to see if a user can attach an rt task to its task group. This looks good to me. Does anybody object to the -ENOSPC return value? Should we introduce -ENOTIME for that? Michael, Alan? > Signed-off-by: Dhaval Giani Acked-by: Peter Zijlstra Ingo, I'll send you the patch once the error issue is settled. > Index: linux-2.6/include/linux/sched.h > =================================================================== > --- linux-2.6.orig/include/linux/sched.h > +++ linux-2.6/include/linux/sched.h > @@ -2320,9 +2320,13 @@ extern long sched_group_rt_runtime(struc > extern int sched_group_set_rt_period(struct task_group *tg, > long rt_period_us); > extern long sched_group_rt_period(struct task_group *tg); > +extern int sched_rt_can_attach(struct task_group *tg, struct task_struct *tsk); > #endif > #endif > > +extern int task_can_switch_user(struct user_struct *up, > + struct task_struct *tsk); > + > #ifdef CONFIG_TASK_XACCT > static inline void add_rchar(struct task_struct *tsk, ssize_t amt) > { > Index: linux-2.6/kernel/sched.c > =================================================================== > --- linux-2.6.orig/kernel/sched.c > +++ linux-2.6/kernel/sched.c > @@ -9466,6 +9466,16 @@ static int sched_rt_global_constraints(v > > return ret; > } > + > +int sched_rt_can_attach(struct task_group *tg, struct task_struct *tsk) > +{ > + /* Don't accept realtime tasks when there is no way for them to run */ > + if (rt_task(tsk) && tg->rt_bandwidth.rt_runtime == 0) > + return 0; > + > + return 1; > +} > + > #else /* !CONFIG_RT_GROUP_SCHED */ > static int sched_rt_global_constraints(void) > { > @@ -9559,8 +9569,7 @@ cpu_cgroup_can_attach(struct cgroup_subs > struct task_struct *tsk) > { > #ifdef CONFIG_RT_GROUP_SCHED > - /* Don't accept realtime tasks when there is no way for them to run */ > - if (rt_task(tsk) && cgroup_tg(cgrp)->rt_bandwidth.rt_runtime == 0) > + if (!sched_rt_can_attach(cgroup_tg(cgrp), tsk)) > return -EINVAL; > #else > /* We don't support RT-tasks being in separate groups */ > Index: linux-2.6/kernel/user.c > =================================================================== > --- linux-2.6.orig/kernel/user.c > +++ linux-2.6/kernel/user.c > @@ -362,6 +362,24 @@ static void free_user(struct user_struct > > #endif > > +#if defined(CONFIG_RT_GROUP_SCHED) && defined(CONFIG_USER_SCHED) > +/* > + * We need to check if a setuid can take place. This function should be called > + * before successfully completing the setuid. > + */ > +int task_can_switch_user(struct user_struct *up, struct task_struct *tsk) > +{ > + > + return sched_rt_can_attach(up->tg, tsk); > + > +} > +#else > +int task_can_switch_user(struct user_struct *up, struct task_struct *tsk) > +{ > + return 1; > +} > +#endif > + > /* > * Locate the user_struct for the passed UID. If found, take a ref on it. The > * caller must undo that ref with free_uid(). > Index: linux-2.6/kernel/sys.c > =================================================================== > --- linux-2.6.orig/kernel/sys.c > +++ linux-2.6/kernel/sys.c > @@ -560,7 +560,7 @@ error: > abort_creds(new); > return retval; > } > - > + > /* > * change the user struct in a credentials set to match the new UID > */ > @@ -572,6 +572,11 @@ static int set_user(struct cred *new) > if (!new_user) > return -EAGAIN; > > + if (!task_can_switch_user(new_user, current)) { > + free_uid(new_user); > + return -ENOSPC; > + } > + > if (atomic_read(&new_user->processes) >= > current->signal->rlim[RLIMIT_NPROC].rlim_cur && > new_user != INIT_USER) { > @@ -632,10 +637,11 @@ SYSCALL_DEFINE2(setreuid, uid_t, ruid, u > goto error; > } > > - retval = -EAGAIN; > - if (new->uid != old->uid && set_user(new) < 0) > - goto error; > - > + if (new->uid != old->uid) { > + retval = set_user(new); > + if (retval < 0) > + goto error; > + } > if (ruid != (uid_t) -1 || > (euid != (uid_t) -1 && euid != old->uid)) > new->suid = new->euid; > @@ -681,9 +687,10 @@ SYSCALL_DEFINE1(setuid, uid_t, uid) > retval = -EPERM; > if (capable(CAP_SETUID)) { > new->suid = new->uid = uid; > - if (uid != old->uid && set_user(new) < 0) { > - retval = -EAGAIN; > - goto error; > + if (uid != old->uid) { > + retval = set_user(new); > + if (retval < 0) > + goto error; > } > } else if (uid != old->uid && uid != new->suid) { > goto error; > @@ -735,11 +742,13 @@ SYSCALL_DEFINE3(setresuid, uid_t, ruid, > goto error; > } > > - retval = -EAGAIN; > if (ruid != (uid_t) -1) { > new->uid = ruid; > - if (ruid != old->uid && set_user(new) < 0) > - goto error; > + if (ruid != old->uid) { > + retval = set_user(new); > + if (retval < 0) > + goto error; > + } > } > if (euid != (uid_t) -1) > new->euid = euid;