tracing: Fix infinite loop in tracing_read_pipe on overflowed print_trace_line

mainline inclusion
from mainline-v6.2-rc1
commit c1ac03af
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I69283
CVE: NA

--------------------------------

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: 088b1e42 ("ftrace: pipe fixes")
Signed-off-by: NYang Jihong <yangjihong1@huawei.com>
Signed-off-by: NSteven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: NYang Jihong <yangjihong1@huawei.com>
Reviewed-by: NZheng Yejian <zhengyejian1@huawei.com>
Reviewed-by: NYe Weihua <yeweihua4@huawei.com>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>

kernel/trace/trace.c

@@ -5771,7 +5771,20 @@ 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;
 		}