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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: Nikita Yushchenko <nikita.yushchenko@virtuozzo.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Nikita Yushchenko 2021-11-18 17:55:16 +03:00 committed by Steven Rostedt (VMware)
parent c4c1dbcc09
commit 2ef75e9bd2
1 changed files with 12 additions and 0 deletions
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12
kernel/trace/trace.c
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@ -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);