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

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Message-ID: <20190206155243.725bc30d@gandalf.local.home>
Date:   Wed, 6 Feb 2019 15:52:43 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.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 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.

-- Steve


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