Commit 2ef75e9b authored by Nikita Yushchenko's avatar Nikita Yushchenko Committed by Steven Rostedt (VMware)
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tracing: Don't use out-of-sync va_list in event printing 

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: default avatarNikita Yushchenko <nikita.yushchenko@virtuozzo.com>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent c4c1dbcc

kernel/trace/trace.c

+12 −0
Original line number Diff line number Diff line
@@ -3812,6 +3812,18 @@ 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);