Commit c8fafb34 authored by Andrea Righi's avatar Andrea Righi Committed by Tejun Heo
Browse files

sched_ext: Avoid NULL scx_root deref in __scx_exit() 



A sched_ext scheduler may trigger __scx_exit() from a BPF timer
callback, where scx_root may not be safely dereferenced.

This can lead to a NULL pointer dereference as shown below (triggered by
scx_tickless):

 BUG: kernel NULL pointer dereference, address: 0000000000000330
...
 CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.14.0-virtme #1 PREEMPT(full)
 RIP: 0010:__scx_exit+0x2b/0x190
...
 Call Trace:
  <IRQ>
  scx_bpf_get_idle_smtmask+0x59/0x80
  bpf_prog_8320d4217989178c_dispatch_all_cpus+0x35/0x1b6
...
  bpf_prog_97f847d871513f95_sched_timerfn+0x4c/0x264
  bpf_timer_cb+0x7a/0x140
  __hrtimer_run_queues+0x1f9/0x3a0
  hrtimer_run_softirq+0x8c/0xd0
  handle_softirqs+0xd3/0x3d0
  __irq_exit_rcu+0x9a/0xc0
  irq_exit_rcu+0xe/0x20

Fix this by checking for a valid scx_root and adding proper RCU
protection.

Fixes: 48e12677 ("sched_ext: Introduce scx_sched")
Signed-off-by: default avatarAndrea Righi <arighi@nvidia.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent c01adf40

kernel/sched/ext.c

+13 −4
Original line number Diff line number Diff line
@@ -5212,12 +5212,19 @@ static void scx_error_irq_workfn(struct irq_work *irq_work) 
static __printf(3, 4) void __scx_exit(enum scx_exit_kind kind, s64 exit_code,

				      const char *fmt, ...)

{

	struct scx_exit_info *ei = scx_root->exit_info;

	struct scx_sched *sch;

	struct scx_exit_info *ei;

	int none = SCX_EXIT_NONE;

	va_list args;



	if (!atomic_try_cmpxchg(&scx_root->exit_kind, &none, kind))

		return;

	rcu_read_lock();

	sch = rcu_dereference(scx_root);

	if (!sch)

		goto out_unlock;

	ei = sch->exit_info;



	if (!atomic_try_cmpxchg(&sch->exit_kind, &none, kind))

		goto out_unlock;



	ei->exit_code = exit_code;

#ifdef CONFIG_STACKTRACE
@@ -5235,7 +5242,9 @@ static __printf(3, 4) void __scx_exit(enum scx_exit_kind kind, s64 exit_code, 
	ei->kind = kind;

	ei->reason = scx_exit_reason(ei->kind);



	irq_work_queue(&scx_root->error_irq_work);

	irq_work_queue(&sch->error_irq_work);

out_unlock:

	rcu_read_unlock();

}



static struct scx_sched *scx_alloc_and_add_sched(struct sched_ext_ops *ops)