Re: [PATCH] ftrace: Fix use-after-free for dynamic ftrace_ops

[Li Huafei <lihuafei1@huawei.com>]

On 2022/11/3 6:53, Steven Rostedt wrote:
> On Tue, 1 Nov 2022 14:41:46 +0800
> Li Huafei <lihuafei1@huawei.com> wrote:
> 
> 
>> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
>> index fbf2543111c0..4219cc2a04a6 100644
>> --- a/kernel/trace/ftrace.c
>> +++ b/kernel/trace/ftrace.c
>> @@ -3030,13 +3030,16 @@ int ftrace_shutdown(struct ftrace_ops *ops, int command)
>>  
>>  	if (!command || !ftrace_enabled) {
> 
> ftrace_enabled is seldom not set. I don't think we even need to check
> it. It's just the value of /proc/sys/kernel/ftrace_enabled, where most
> people don't even know that file exists. I do want to get rid of it one
> day too. So let's not optimize for it.
> 

Agree. The code will look much simpler this way.

>>  		/*
>> -		 * If these are dynamic or per_cpu ops, they still
>> -		 * need their data freed. Since, function tracing is
>> -		 * not currently active, we can just free them
>> -		 * without synchronizing all CPUs.
>> +		 * If these are dynamic, they still need their data freed. If
>> +		 * function tracing is currently active, we neet to synchronize
>> +		 * all CPUs before we can release them.
>>  		 */
>> -		if (ops->flags & FTRACE_OPS_FL_DYNAMIC)
>> +		if (ops->flags & FTRACE_OPS_FL_DYNAMIC) {
>> +			if (ftrace_enabled)
>> +				goto sync_rcu;
>> +
>>  			goto free_ops;
> 
> Change the above just to "goto out;"
> 
>> +		}
>>  
>>  		return 0;
>>  	}
>> @@ -3083,6 +3086,7 @@ int ftrace_shutdown(struct ftrace_ops *ops, int command)
>>  	 * ops.
>>  	 */
> 
> Add here:
> 
>  out:
> 
>>  	if (ops->flags & FTRACE_OPS_FL_DYNAMIC) {
>> + sync_rcu:
>>  		/*
>>  		 * We need to do a hard force of sched synchronization.
>>  		 * This is because we use preempt_disable() to do RCU, but
> 
> And get rid of the labels in the if block.
> 

Will make the above changes in v2, thanks!

> Thanks!
> 
> -- Steve
> 
> .
>