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

Hillf Danton
2024-04-30T22:50:05Z

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;

--