[PATCH 5.15 049/207] tracing: Dont use out-of-sync va_list in event printing

Greg Kroah-Hartman
2021-12-06T15:49:37Z

From: Nikita Yushchenko <nikita.yushchenko@virtuozzo.com>

[ Upstream commit 2ef75e9bd2c998f1c6f6f23a3744136105ddefd5 ]

If trace_seq becomes full, trace_seq_vprintf() no longer consumes
arguments from va_list, making va_list out of sync with format
processing by trace_check_vprintf().

This causes va_arg() in trace_check_vprintf() to return wrong
positional argument, which results into a WARN_ON_ONCE() hit.

ftrace_stress_test from LTP triggers this situation.

Fix it by explicitly avoiding further use if va_list at the point
when it's consistency can no longer be guaranteed.

Link: https://lkml.kernel.org/r/20211118145516.13219-1-nikita.yushchenko@virtuozzo.com

Signed-off-by: Nikita Yushchenko <nikita.yushchenko@virtuozzo.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/trace/trace.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5e452dd57af01..18db461f77cdf 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3836,6 +3836,18 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
iter->fmt[i] = '\0';
trace_seq_vprintf(&iter->seq, iter->fmt, ap);

+ /*
+ * If iter->seq is full, the above call no longer guarantees
+ * that ap is in sync with fmt processing, and further calls
+ * to va_arg() can return wrong positional arguments.
+ *
+ * Ensure that ap is no longer used in this case.
+ */
+ if (iter->seq.full) {
+ p = "";
+ break;
+ }
+
if (star)
len = va_arg(ap, int);

--
2.33.0