[PATCH v3] tracing: Fix infinite loop in tracing_read_pipe on overflowed print_trace_line

From: Yang Jihong
Date: Thu Nov 24 2022 - 08:02:28 EST


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@xxxxxxxxxx>
---
kernel/trace/trace.c | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a7fe0e115272..55733224fa88 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6787,7 +6787,27 @@ 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 it, otherwise,
+ * while loop will peek this event next time,
+ * resulting in an infinite loop.
+ */
+ if (trace_seq_has_overflowed(&iter->seq)) {
+ /*
+ * Here we only consider the case that one
+ * print_trace_line() fills the entire trace_seq
+ * in one shot, in that case, iter->seq.seq.len is zero,
+ * we simply output a log of too long line to inform the user.
+ */
+ 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;
}
--
2.30.GIT