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sched: don't allow setuid to succeed if the user does not have rt bandwidth

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Impact: fix hung task with certain (non-default) rt-limit settings

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.
On failure, return EINVAL, which is also returned in
CONFIG_CGROUP_SCHED.

Reported-by: Corey Hickey <bugfood-ml@fatooh.org>
Signed-off-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Dhaval Giani 2009-02-27 15:13:54 +05:30 committed by Ingo Molnar
parent cac64d00c2
commit 54e9912428
4 changed files with 53 additions and 13 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

4
include/linux/sched.h
View file

@ -2291,9 +2291,13 @@ extern long sched_group_rt_runtime(struct task_group *tg);
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)
{

13
kernel/sched.c
View file

@ -9224,6 +9224,16 @@ static int sched_rt_global_constraints(void)
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)
{
@ -9317,8 +9327,7 @@ cpu_cgroup_can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
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 */

31
kernel/sys.c
View file

@ -559,7 +559,7 @@ error:
abort_creds(new);
return retval;
}
/*
* change the user struct in a credentials set to match the new UID
*/
@ -571,6 +571,11 @@ 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 -EINVAL;
}
if (atomic_read(&new_user->processes) >=
current->signal->rlim[RLIMIT_NPROC].rlim_cur &&
new_user != INIT_USER) {
@ -631,10 +636,11 @@ SYSCALL_DEFINE2(setreuid, uid_t, ruid, uid_t, euid)
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;
@ -680,9 +686,10 @@ 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;
@ -734,11 +741,13 @@ SYSCALL_DEFINE3(setresuid, uid_t, ruid, uid_t, euid, uid_t, suid)
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;

18
kernel/user.c
View file

@ -362,6 +362,24 @@ static void free_user(struct user_struct *up, unsigned long flags)
#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().