linux-kernel - [for-linus][PATCH 5/8] tracing/synthetic: Allocate one additional element for size

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Message-ID: <20230822023842.120843765@goodmis.org>
Date:   Mon, 21 Aug 2023 22:38:08 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sven Schnelle <svens@...ux.ibm.com>
Subject: [for-linus][PATCH 5/8] tracing/synthetic: Allocate one additional element for size

From: Sven Schnelle <svens@...ux.ibm.com>

While debugging another issue I noticed that the stack trace contains one
invalid entry at the end:

<idle>-0       [008] d..4.    26.484201: wake_lat: pid=0 delta=2629976084 000000009cc24024 stack=STACK:
=> __schedule+0xac6/0x1a98
=> schedule+0x126/0x2c0
=> schedule_timeout+0x150/0x2c0
=> kcompactd+0x9ca/0xc20
=> kthread+0x2f6/0x3d8
=> __ret_from_fork+0x8a/0xe8
=> 0x6b6b6b6b6b6b6b6b

This is because the code failed to add the one element containing the
number of entries to field_size.

Link: https://lkml.kernel.org/r/20230816154928.4171614-4-svens@linux.ibm.com

Cc: Masami Hiramatsu <mhiramat@...nel.org>
Fixes: 00cf3d672a9d ("tracing: Allow synthetic events to pass around stacktraces")
Signed-off-by: Sven Schnelle <svens@...ux.ibm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 kernel/trace/trace_events_synth.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index 80a2a832f857..9897d0bfcab7 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -528,7 +528,8 @@ static notrace void trace_event_raw_event_synth(void *__data,
 		str_val = (char *)(long)var_ref_vals[val_idx];
 
 		if (event->dynamic_fields[i]->is_stack) {
-			len = *((unsigned long *)str_val);
+			/* reserve one extra element for size */
+			len = *((unsigned long *)str_val) + 1;
 			len *= sizeof(unsigned long);
 		} else {
 			len = fetch_store_strlen((unsigned long)str_val);
-- 
2.40.1