Re: [PATCH v3] ftrace: Fix possible use-after-free issue in ftrace_location()

[Zheng Yejian]

On 2024/5/3 05:07, Steven Rostedt wrote:
> On Wed, 17 Apr 2024 11:28:30 +0800
> Zheng Yejian <zhengyejian1@xxxxxxxxxx> 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;
> > +}