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

[Edward Adam Davis <eadavis@qq.com>]

please test uaf in vhost_task_fn

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

diff --git a/kernel/softirq.c b/kernel/softirq.c
index b315b21fb28c..02582017759a 100644
--- 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 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 		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 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 	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;
diff --git a/kernel/vhost_task.c b/kernel/vhost_task.c
index 48c289947b99..8800f5acc007 100644
--- a/kernel/vhost_task.c
+++ b/kernel/vhost_task.c
@@ -61,8 +61,8 @@ static int vhost_task_fn(void *data)
 		set_bit(VHOST_TASK_FLAGS_KILLED, &vtsk->flags);
 		vtsk->handle_sigkill(vtsk->data);
 	}
-	complete(&vtsk->exited);
 	mutex_unlock(&vtsk->exit_mutex);
+	complete(&vtsk->exited);
 
 	do_exit(0);
 }