tracing: Fix infinite loop in tracing_read_pipe on overflowed print_trace_line

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@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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 459ff8c..3076af8 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6797,7 +6797,20 @@ 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;
                }