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Subject: Re: [PATCH v4] tracing: Fix infinite loop in tracing_read_pipe on
 overflowed print_trace_line
To:     <rostedt@goodmis.org>, <mhiramat@kernel.org>,
        <linux-kernel@vger.kernel.org>
References: <20221129113009.182425-1-yangjihong1@huawei.com>
From:   Yang Jihong <yangjihong1@huawei.com>
Message-ID: <46733774-295a-ade9-497d-6e73c6c468de@huawei.com>
Date:   Mon, 12 Dec 2022 10:57:08 +0800
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Hello,

PING.

Are there any other problems with this patch?

Thanks,
Yang.

On 2022/11/29 19:30, Yang Jihong wrote:
> print_trace_line may overflow seq_file buffer. If the event is not
> consumed, the while loop keeps peeking this event, causing a infinite loop.
> 
> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
> ---
>   kernel/trace/trace.c | 15 ++++++++++++++-
>   1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index a7fe0e115272..de7c99f4b539 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -6787,7 +6787,20 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
>   
>   		ret = print_trace_line(iter);
>   		if (ret == TRACE_TYPE_PARTIAL_LINE) {
> -			/* don't print partial lines */
> +			/*
> +			 * If one print_trace_line() fills entire trace_seq in one shot,
> +			 * trace_seq_to_user() will returns -EBUSY because save_len == 0,
> +			 * In this case, we need to consume it, otherwise, loop will peek
> +			 * this event next time, resulting in an infinite loop.
> +			 */
> +			if (save_len == 0) {
> +				iter->seq.full = 0;
> +				trace_seq_puts(&iter->seq, "[LINE TOO BIG]\n");
> +				trace_consume(iter);
> +				break;
> +			}
> +
> +			/* In other cases, don't print partial lines */
>   			iter->seq.seq.len = save_len;
>   			break;
>   		}
>