linux-kernel - Re: [PATCH v3] ftrace: Fix possible use-after-free issue in ftrace

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Date: Thu, 9 May 2024 09:39:06 +0800
From: Zheng Yejian <zhengyejian1@...wei.com>
To: Steven Rostedt <rostedt@...dmis.org>
CC: <mhiramat@...nel.org>, <mark.rutland@....com>,
	<mathieu.desnoyers@...icios.com>, <Markus.Elfring@....de>,
	<linux-kernel@...r.kernel.org>, <linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] ftrace: Fix possible use-after-free issue in
 ftrace_location()

On 2024/5/3 05:07, Steven Rostedt wrote:
> On Wed, 17 Apr 2024 11:28:30 +0800
> Zheng Yejian <zhengyejian1@...wei.com> wrote:
> 
>> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
>> index da1710499698..e05d3e3dc06a 100644
>> --- a/kernel/trace/ftrace.c
>> +++ b/kernel/trace/ftrace.c
>> @@ -1581,7 +1581,7 @@ static struct dyn_ftrace *lookup_rec(unsigned long start, unsigned long end)
>>   }
>>   
>>   /**
>> - * ftrace_location_range - return the first address of a traced location
>> + * ftrace_location_range_rcu - return the first address of a traced location
> 
> kerneldoc comments are for external functions. You need to move this down
> to ftrace_location_range() as here you are commenting a local static function.

I'll do it in v4.

> 
> But I have to ask, why did you create this static function anyway? There's
> only one user of it (the ftrace_location_range()). Why didn't you just
> simply add the rcu locking there?

Yes, the only-one-user function looks ugly.
At first thought that ftrace_location_range() needs to a lock, I just do like that,
no specital reason.

> 
> unsigned long ftrace_location_range(unsigned long start, unsigned long end)
> {
> 	struct dyn_ftrace *rec;
> 	unsigned long ip = 0;
> 
> 	rcu_read_lock();
> 	rec = lookup_rec(start, end);
> 	if (rec)
> 		ip = rec->ip;
> 	rcu_read_unlock();
> 
> 	return ip;
> }
> 
> -- Steve
> 
> 
>>    *	if it touches the given ip range
>>    * @start: start of range to search.
>>    * @end: end of range to search (inclusive). @end points to the last byte
>> @@ -1592,7 +1592,7 @@ static struct dyn_ftrace *lookup_rec(unsigned long start, unsigned long end)
>>    * that is either a NOP or call to the function tracer. It checks the ftrace
>>    * internal tables to determine if the address belongs or not.
>>    */
>> -unsigned long ftrace_location_range(unsigned long start, unsigned long end)
>> +static unsigned long ftrace_location_range_rcu(unsigned long start, unsigned long end)
>>   {
>>   	struct dyn_ftrace *rec;
>>   
>> @@ -1603,6 +1603,16 @@ unsigned long ftrace_location_range(unsigned long start, unsigned long end)
>>   	return 0;
>>   }
>>   
>> +unsigned long ftrace_location_range(unsigned long start, unsigned long end)
>> +{
>> +	unsigned long loc;
>> +
>> +	rcu_read_lock();
>> +	loc = ftrace_location_range_rcu(start, end);
>> +	rcu_read_unlock();
>> +	return loc;
>> +}
>