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Subject[for-next][PATCH 1/8] tracing: Fix infinite loop in tracing_read_pipe on overflowed print_trace_line
From: Yang Jihong <yangjihong1@huawei.com>

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@huawei.com

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: stable@vger.kernel.org
Fixes: 088b1e427dbba ("ftrace: pipe fixes")
Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
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 664619b3f1e1..548890c7c0f5 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6802,7 +6802,20 @@ 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;
}
--
2.35.1

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