From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7A739C4332F for ; Sun, 20 Nov 2022 19:39:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229671AbiKTTi7 (ORCPT ); Sun, 20 Nov 2022 14:38:59 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44366 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229449AbiKTTi6 (ORCPT ); Sun, 20 Nov 2022 14:38:58 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7177221245 for ; Sun, 20 Nov 2022 11:38:57 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 24DDEB80B4D for ; Sun, 20 Nov 2022 19:38:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 424CEC433D6; Sun, 20 Nov 2022 19:38:54 +0000 (UTC) Date: Sun, 20 Nov 2022 14:38:52 -0500 From: Steven Rostedt To: Yang Jihong Cc: , Subject: Re: [PATCH v2] tracing: Fix infinite loop in tracing_read_pipe on overflowed print_trace_line Message-ID: <20221120143852.7e84b50d@rorschach.local.home> In-Reply-To: <20221118102521.62362-1-yangjihong1@huawei.com> References: <20221118102521.62362-1-yangjihong1@huawei.com> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 18 Nov 2022 18:25:21 +0800 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 > --- > > Changes since v1: > - Print partial line to show the broken trace event when overflowed print_trace_line > > kernel/trace/trace.c | 27 ++++++++++++++++++++++++++- > 1 file changed, 26 insertions(+), 1 deletion(-) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 47a44b055a1d..81c36dc80212 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -6786,7 +6786,32 @@ 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 trace_line of the tracer overflows seq_file > + * buffer, trace_seq_to_user returns -EBUSY. > + * In this case, we need to consume, otherwise, > + * while loop will peek this event next time, > + * resulting in an infinite loop. > + */ > + if (trace_seq_has_overflowed(&iter->seq)) { We need to only do this if save_len is zero. Because the reason that it returns TRACE_TYPE_PARTIAL_LINE is usually because it overflowed. This loops until the trace_seq is full, so it's OK to have it overflow. The case I believe you are fixing, is the case were one print_trace_line() actually fills the entire trace_seq in one shot. In which case, it will never print, and in that case, save_len will be zero. -- Steve > + /* > + * Print the partial line, > + * that way we can see the broken trace event. > + */ > + char dots[] = "...\n"; > + > + iter->seq.full = 0; > + if (seq_buf_buffer_left(&iter->seq.seq) < strlen(dots)) { > + iter->seq.seq.len = > + seq_buf_used(&iter->seq.seq) - strlen(dots); > + } > + trace_seq_puts(&iter->seq, dots); > + > + trace_consume(iter); > + break; > + } > + > + /* In other cases, don't print partial lines */ > iter->seq.seq.len = save_len; > break; > }