From b6e8d40d43ae4dec00c8fea2593eeea3114b8f44 Mon Sep 17 00:00:00 2001

From: Waiman Long <longman@redhat.com>

Date: Tue, 2 Aug 2022 21:54:51 -0400

Subject: [PATCH] sched, cpuset: Fix dl_cpu_busy() panic due to empty

 cs->cpus_allowed

Git-commit: b6e8d40d43ae4dec00c8fea2593eeea3114b8f44

Patch-mainline: v6.0-rc1

References: git-fixes

With cgroup v2, the cpuset's cpus_allowed mask can be empty indicating

that the cpuset will just use the effective CPUs of its parent. So

cpuset_can_attach() can call task_can_attach() with an empty mask.

This can lead to cpumask_any_and() returns nr_cpu_ids causing the call

to dl_bw_of() to crash due to percpu value access of an out of bound

CPU value. For example:

	[80468.182258] BUG: unable to handle page fault for address: ffffffff8b6648b0

	  :

	[80468.191019] RIP: 0010:dl_cpu_busy+0x30/0x2b0

	  :

	[80468.207946] Call Trace:

	[80468.208947]  cpuset_can_attach+0xa0/0x140

	[80468.209953]  cgroup_migrate_execute+0x8c/0x490

	[80468.210931]  cgroup_update_dfl_csses+0x254/0x270

	[80468.211898]  cgroup_subtree_control_write+0x322/0x400

	[80468.212854]  kernfs_fop_write_iter+0x11c/0x1b0

	[80468.213777]  new_sync_write+0x11f/0x1b0

	[80468.214689]  vfs_write+0x1eb/0x280

	[80468.215592]  ksys_write+0x5f/0xe0

	[80468.216463]  do_syscall_64+0x5c/0x80

	[80468.224287]  entry_SYSCALL_64_after_hwframe+0x44/0xae

Fix that by using effective_cpus instead. For cgroup v1, effective_cpus

is the same as cpus_allowed. For v2, effective_cpus is the real cpumask

to be used by tasks within the cpuset anyway.

Also update task_can_attach()'s 2nd argument name to cs_effective_cpus to

reflect the change. In addition, a check is added to task_can_attach()

to guard against the possibility that cpumask_any_and() may return a

value >= nr_cpu_ids.

Fixes: 7f51412a415d ("sched/deadline: Fix bandwidth check/update when migrating tasks between exclusive cpusets")

Signed-off-by: Waiman Long <longman@redhat.com>

Signed-off-by: Ingo Molnar <mingo@kernel.org>

Acked-by: Juri Lelli <juri.lelli@redhat.com>

Link: https://lore.kernel.org/r/20220803015451.2219567-1-longman@redhat.com

Signed-off-by: Frederic Weisbecker <fweisbecker@suse.com>

---

 include/linux/sched.h  | 2 +-

 kernel/cgroup/cpuset.c | 2 +-

 kernel/sched/core.c    | 8 +++++---

 3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h

index 88b8817b827d..6a060160f0db 100644

--- a/include/linux/sched.h

+++ b/include/linux/sched.h

@@ -1813,7 +1813,7 @@ current_restore_flags(unsigned long orig_flags, unsigned long flags)

 }

 extern int cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);

-extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_cpus_allowed);

+extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_effective_cpus);

 #ifdef CONFIG_SMP

 extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask);

 extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask);

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c

index 71a418858a5e..58aadfda9b8b 100644

--- a/kernel/cgroup/cpuset.c

+++ b/kernel/cgroup/cpuset.c

@@ -2239,7 +2239,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)

 		goto out_unlock;

 	cgroup_taskset_for_each(task, css, tset) {

-		ret = task_can_attach(task, cs->cpus_allowed);

+		ret = task_can_attach(task, cs->effective_cpus);

 		if (ret)

 			goto out_unlock;

 		ret = security_task_setscheduler(task);

diff --git a/kernel/sched/core.c b/kernel/sched/core.c

index 5555e49c4e12..addc3c2d2122 100644

--- a/kernel/sched/core.c

+++ b/kernel/sched/core.c

@@ -8980,7 +8980,7 @@ int cpuset_cpumask_can_shrink(const struct cpumask *cur,

 }

 int task_can_attach(struct task_struct *p,

-		    const struct cpumask *cs_cpus_allowed)

+		    const struct cpumask *cs_effective_cpus)

 {

 	int ret = 0;

@@ -8999,9 +8999,11 @@ int task_can_attach(struct task_struct *p,

 	}

 	if (dl_task(p) && !cpumask_intersects(task_rq(p)->rd->span,

-					      cs_cpus_allowed)) {

-		int cpu = cpumask_any_and(cpu_active_mask, cs_cpus_allowed);

+					      cs_effective_cpus)) {

+		int cpu = cpumask_any_and(cpu_active_mask, cs_effective_cpus);

+		if (unlikely(cpu >= nr_cpu_ids))

+			return -EINVAL;

 		ret = dl_cpu_busy(cpu, p);

 	}

-- 

2.34.1