linux-kernel - Re: [PATCH] tracing/fprobe: Fix to check whether fprobe is registered correctly

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Date:   Tue, 25 Oct 2022 23:36:39 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>,
        Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH] tracing/fprobe: Fix to check whether fprobe is
 registered correctly

On Mon, 24 Oct 2022 10:22:30 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Sun, 23 Oct 2022 23:19:33 +0900
> "Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:
> 
> > From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> > 
> > Since commit ab51e15d535e ("fprobe: Introduce FPROBE_FL_KPROBE_SHARED flag
> > for fprobe") introduced fprobe_kprobe_handler() for fprobe::f_op::func,
> > unregister_fprobe() fails to unregister the registered if user specifies
> > FPROBE_FL_KPROBE_SHARED flag.
> > To check it correctly, it should confirm the fprobe::f_op::func is either
> > fprobe_handler() or fprobe_kprobe_handler().
> > 
> > Fixes: ab51e15d535e ("fprobe: Introduce FPROBE_FL_KPROBE_SHARED flag for fprobe")
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> > ---
> >  kernel/trace/fprobe.c |    3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
> > index aac63ca9c3d1..9000d8ea6274 100644
> > --- a/kernel/trace/fprobe.c
> > +++ b/kernel/trace/fprobe.c
> > @@ -301,7 +301,8 @@ int unregister_fprobe(struct fprobe *fp)
> >  {
> >  	int ret;
> >  
> > -	if (!fp || fp->ops.func != fprobe_handler)
> > +	if (!fp || (fp->ops.func != fprobe_handler &&
> > +		    fp->ops.func != fprobe_kprobe_handler))
> >  		return -EINVAL;
> >  
> >  	/*
> 
> Should we make this more paranoid?
> 
> 	if (!fp ||
> 	    (fprobe_shared_with_kprobes(fp) && fp->ops.func != fprobe_kprobe_handler) ||
> 	    (!fprobe_shared_with_kprobes(fp) && fp->ops.func != fprobe_handler))
> 
> Or is that over-kill?

Yeah, I think it is over-kill since this is just for a safety check, like
checking NULL in free(). Or, are there any way to check the ftrace_ops is
registered?

Thank you,

> 
> -- Steve


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>