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Message-Id: <1234869339.4744.77.camel@laptop>
Date: Tue, 17 Feb 2009 12:15:39 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Dhaval Giani <dhaval@...ux.vnet.ibm.com>
Cc: Corey Hickey <bugfood-ml@...ooh.org>, linux-kernel@...r.kernel.org,
Bharata B Rao <bharata@...ux.vnet.ibm.com>,
Balbir Singh <balbir@...ibm.com>,
Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...e.hu>, mtk.manpages@...il.com,
Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: RT scheduling and a way to make a process hang, unkillable
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 <dhaval@...ux.vnet.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
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;
--
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