This is a note to let you know that I've just added the patch titled tracing: Fix infinite loop in tracing_read_pipe on overflowed print_trace_line to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: tracing-fix-infinite-loop-in-tracing_read_pipe-on-overflowed-print_trace_line.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From c1ac03af6ed45d05786c219d102f37eb44880f28 Mon Sep 17 00:00:00 2001 From: Yang Jihong <yangjihong1@xxxxxxxxxx> Date: Tue, 29 Nov 2022 19:30:09 +0800 Subject: tracing: Fix infinite loop in tracing_read_pipe on overflowed print_trace_line From: Yang Jihong <yangjihong1@xxxxxxxxxx> commit c1ac03af6ed45d05786c219d102f37eb44880f28 upstream. 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. Link: https://lkml.kernel.org/r/20221129113009.182425-1-yangjihong1@xxxxxxxxxx Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Fixes: 088b1e427dbba ("ftrace: pipe fixes") Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx> Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/trace/trace.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -5803,7 +5803,20 @@ waitagain: 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; } Patches currently in stable-queue which might be from yangjihong1@xxxxxxxxxx are queue-4.19/perf-debug-set-debug_peo_args-and-redirect_to_stderr.patch queue-4.19/blktrace-fix-output-non-blktrace-event-when-blk_clas.patch queue-4.19/tracing-fix-infinite-loop-in-tracing_read_pipe-on-overflowed-print_trace_line.patch