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SubjectRe: [PATCH] ftrace: Fix use-after-free for dynamic ftrace_ops
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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
>
> .
>

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