linux-kernel - Re: [PATCH v2 1/3] tracing: uprobes: Re-enable $comm support for uprobe events

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Message-Id: <20190208094220.83ae0df5c71a9cd8891e598d@kernel.org>
Date:   Fri, 8 Feb 2019 09:42:20 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Andreas Ziegler <andreas.ziegler@....de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] tracing: uprobes: Re-enable $comm support for
 uprobe events

On Wed, 6 Feb 2019 15:52:43 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Fri, 18 Jan 2019 13:44:25 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:
> 
> > @@ -180,7 +183,12 @@ fetch_store_strlen(unsigned long addr)
> >  	int len;
> >  	void __user *vaddr = (void __force __user *) addr;
> >  
> > -	len = strnlen_user(vaddr, MAX_STRING_SIZE);
> > +	if (addr == (unsigned long)current->comm) {
> > +		len = strlen(current->comm);
> > +		if (len)
> > +			len++;
> 
> Why only add 1 if len is non zero? Why not always do it.
> 
> One thing, len should always be greater than 0, and the other is that
> this makes it inconsistent with the NULL case of reading the address in
> userspace.

Agreed, it should not 0, so it should be;
len = strlen(current->comm) + 1;

Thank you!

> 
> -- Steve
> 
> 
> > +	} else
> > +		len = strnlen_user(vaddr, MAX_STRING_SIZE);
> >  
> >  	return (len > MAX_STRING_SIZE) ? 0 : len;


-- 
Masami Hiramatsu <mhiramat@...nel.org>