linux-kernel - [PATCH] tracing: Fix race where eprobes can be called before the event

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Message-ID: <20221117214249.2addbe10@gandalf.local.home>
Date:   Thu, 17 Nov 2022 21:42:49 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     LKML <linux-kernel@...r.kernel.org>,
        Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Rafael Mendonca <rafaelmendsr@...il.com>,
        Tzvetomir Stoyanov <tz.stoyanov@...il.com>,
        Tom Zanussi <zanussi@...nel.org>
Subject: [PATCH] tracing: Fix race where eprobes can be called before the
 event

From: "Steven Rostedt (Google)" <rostedt@...dmis.org>

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/

Cc: stable@...r.kernel.org
Fixes: 7491e2c442781 ("tracing: Add a probe that attaches to trace events")
Reported-by: Rafael Mendonca <rafaelmendsr@...il.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 kernel/trace/trace_eprobe.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
index 5dd0617e5df6..6b31b74954d9 100644
--- a/kernel/trace/trace_eprobe.c
+++ b/kernel/trace/trace_eprobe.c
@@ -563,6 +563,9 @@ 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);
 }
 
-- 
2.35.1