From: Steven Rostedt (Google) <rostedt@goodmis.org>
Date: Fri, 18 Nov 2022 02:42:49 +0000 (-0500)
Subject: tracing: Fix race where eprobes can be called before the event
X-Git-Tag: v6.0.10~111
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=73f5191467ffe3af82f27fe0ea6a8c2fac724d3f;p=thirdparty%2Fkernel%2Fstable.git

tracing: Fix race where eprobes can be called before the event

commit 94eedf3dded5fb472ce97bfaf3ac1c6c29c35d26 upstream.

The flag that tells the event to call its triggers after reading the event
is set for eprobes after the eprobe is enabled. This leads to a race where
the eprobe may be triggered at the beginning of the event where the record
information is NULL. The eprobe then dereferences the NULL record causing
a NULL kernel pointer bug.

Test for a NULL record to keep this from happening.

Link: https://lore.kernel.org/linux-trace-kernel/20221116192552.1066630-1-rafaelmendsr@gmail.com/
Link: https://lore.kernel.org/linux-trace-kernel/20221117214249.2addbe10@gandalf.local.home

Cc: Linux Trace Kernel <linux-trace-kernel@vger.kernel.org>
Cc: Tzvetomir Stoyanov <tz.stoyanov@gmail.com>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: stable@vger.kernel.org
Fixes: 7491e2c442781 ("tracing: Add a probe that attaches to trace events")
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reported-by: Rafael Mendonca <rafaelmendsr@gmail.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_eprobe.c b/kernel/trace/trace_eprobe.c
index 860f5fb9514d7..3b055aaee89a9 100644
--- a/kernel/trace/trace_eprobe.c
+++ b/kernel/trace/trace_eprobe.c
@@ -560,6 +560,9 @@ static void eprobe_trigger_func(struct event_trigger_data *data,
 {
 	struct eprobe_data *edata = data->private_data;
 
+	if (unlikely(!rec))
+		return;
+
 	__eprobe_trace_func(edata, rec);
 }