Re: [syzbot] [net?] [virt?] [kvm?] KASAN: slab-use-after-free Read in vhost_task_fn

[Hillf Danton <hdanton@sina.com>]

On Tue, 30 Apr 2024 01:25:26 -0700
> syzbot found the following issue on:
> 
> HEAD commit:    bb7a2467e6be Add linux-next specific files for 20240426
> git tree:       linux-next
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16c30028980000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git  bb7a2467e6be

--- x/kernel/vhost_task.c
+++ y/kernel/vhost_task.c
@@ -100,6 +100,8 @@ void vhost_task_stop(struct vhost_task *
 	 * freeing it below.
 	 */
 	wait_for_completion(&vtsk->exited);
+	mutex_lock(&vtsk->exit_mutex);
+	mutex_unlock(&vtsk->exit_mutex);
 	kfree(vtsk);
 }
 EXPORT_SYMBOL_GPL(vhost_task_stop);
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -508,7 +508,7 @@ static inline bool lockdep_softirq_start(void) { return false; }
 static inline void lockdep_softirq_end(bool in_hardirq) { }
 #endif
 
-asmlinkage __visible void __softirq_entry __do_softirq(void)
+static void handle_softirqs(bool ksirqd)
 {
 	unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
 	unsigned long old_flags = current->flags;
@@ -563,8 +563,7 @@ restart:
 		pending >>= softirq_bit;
 	}
 
-	if (!IS_ENABLED(CONFIG_PREEMPT_RT) &&
-	    __this_cpu_read(ksoftirqd) == current)
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT) && ksirqd)
 		rcu_softirq_qs();
 
 	local_irq_disable();
@@ -584,6 +583,11 @@ restart:
 	current_restore_flags(old_flags, PF_MEMALLOC);
 }
 
+asmlinkage __visible void __softirq_entry __do_softirq(void)
+{
+	handle_softirqs(false);
+}
+
 /**
  * irq_enter_rcu - Enter an interrupt context with RCU watching
  */
@@ -921,7 +925,7 @@ static void run_ksoftirqd(unsigned int cpu)
 		 * We can safely run softirq on inline stack, as we are not deep
 		 * in the task stack here.
 		 */
-		__do_softirq();
+		handle_softirqs(true);
 		ksoftirqd_run_end();
 		cond_resched();
 		return;

--