linux-kernel - Re: [PATCH] tracing: Correct the refcount for hist/hist_debug file if single

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Message-ID: <20250313104446.7b31820e@batman.local.home>
Date: Thu, 13 Mar 2025 10:44:46 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Tengda Wu <wutengda@...weicloud.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Zheng Yejian <zhengyejian1@...wei.com>,
 linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: Correct the refcount for hist/hist_debug file
 if single_open() fails

On Thu, 13 Mar 2025 10:37:19 +0000
Tengda Wu <wutengda@...weicloud.com> wrote:

> The function event_{hist,hist_debug}_open() maintains the refcount of
> 'file->tr' and 'file' through tracing_open_file_tr(), but it does not
> roll back these counts when the subsequent single_open() call fails,
> leading to a refcount leak.
> 
> A very obvious case is that if the hist/hist_debug file belongs to a
> certain instance, the failure of single_open() will prevent the deletion
> of that instance, as it relies on the condition 'tr->ref == 1' within
> __remove_instance().
> 
> Fix this by calling tracing_release_file_tr() to correct the refcount
> when single_open() fails.
> 
> Fixes: 1cc111b9cddc ("tracing: Fix uaf issue when open the hist or hist_debug file")
> Signed-off-by: Tengda Wu <wutengda@...weicloud.com>
> Cc: stable@...r.kernel.org # v6.7+
> ---
>  kernel/trace/trace_events_hist.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index ad7419e24055..900b06fa8505 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -5702,8 +5702,10 @@ static int event_hist_open(struct inode *inode, struct file *file)
>  	/* Clear private_data to avoid warning in single_open() */
>  	file->private_data = NULL;
>  	ret = single_open(file, hist_show, hist_file);
> -	if (ret)
> +	if (ret) {
>  		kfree(hist_file);
> +		tracing_release_file_tr(inode, file);
> +	}

Hmm, this function has a couple more error path exits after taking the
ref count. If this is to be fixed, let's fix it completely. Each of
those error paths need to call tracing_release_file_tr().

-- Steve


>  
>  	return ret;
>  }
> @@ -5979,7 +5981,10 @@ static int event_hist_debug_open(struct inode *inode, struct file *file)
>  
>  	/* Clear private_data to avoid warning in single_open() */
>  	file->private_data = NULL;
> -	return single_open(file, hist_debug_show, file);
> +	ret = single_open(file, hist_debug_show, file);
> +	if (ret)
> +		tracing_release_file_tr(inode, file);
> +	return ret;
>  }
>  
>  const struct file_operations event_hist_debug_fops = {