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Date: Tue, 17 Feb 2009 15:45:43 +0530
From: Dhaval Giani <dhaval@...ux.vnet.ibm.com>
To: Corey Hickey <bugfood-ml@...ooh.org>
Cc: Peter Zijlstra <peterz@...radead.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
Subject: Re: RT scheduling and a way to make a process hang, unkillable
> This was on top of tip I think. But yeah, that would be expected.
> Yesterday was really not working out, I figured out this one, and had
> fixed this in the next version. I have a better patch arond here.
>
This is on top of tip, and should have everything fixed up.
/me has his fingers crossed :)
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.
Changes from v5:
1. free up the user struct on failure
2. Use the user struct obtained in set_user
3. Change the return value to ENOSPC, since this makes more sense, we do
not have RT runtime available to us.
Changes from v4:
1. Check if find_user returns a valid user struct.
Changes from v3:
1. Actually fix the leak.
Changes from v2:
1. Patch compiles for CONFIG_CGROUP_SCHED as well
2. Fix two memory leaks.
Changes from v1:
1. Peter suggested that rt_task_can_change_user should be renamed to
task_can_change_user
2. Changed sched_rt_can_attach to boolean.
Signed-off-by: Dhaval Giani <dhaval@...ux.vnet.ibm.com>
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;
--
regards,
Dhaval
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