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Date: Mon, 03 Apr 2023 17:21:26 -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>,
stable@...r.kernel.org, Matthias Brugger <matthias.bgg@...il.com>,
AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com>,
"Tom Zanussi" <zanussi@...nel.org>,
Tze-nan Wu <Tze-nan.Wu@...iatek.com>
Subject: [for-linus][PATCH 1/6] tracing/synthetic: Fix races on freeing last_cmd
From: Tze-nan Wu <Tze-nan.Wu@...iatek.com>
Currently, the "last_cmd" variable can be accessed by multiple processes
asynchronously when multiple users manipulate synthetic_events node
at the same time, it could lead to use-after-free or double-free.
This patch add "lastcmd_mutex" to prevent "last_cmd" from being accessed
asynchronously.
================================================================
It's easy to reproduce in the KASAN environment by running the two
scripts below in different shells.
script 1:
while :
do
echo -n -e '\x88' > /sys/kernel/tracing/synthetic_events
done
script 2:
while :
do
echo -n -e '\xb0' > /sys/kernel/tracing/synthetic_events
done
================================================================
double-free scenario:
process A process B
------------------- ---------------
1.kstrdup last_cmd
2.free last_cmd
3.free last_cmd(double-free)
================================================================
use-after-free scenario:
process A process B
------------------- ---------------
1.kstrdup last_cmd
2.free last_cmd
3.tracing_log_err(use-after-free)
================================================================
Appendix 1. KASAN report double-free:
BUG: KASAN: double-free in kfree+0xdc/0x1d4
Free of addr ***** by task sh/4879
Call trace:
...
kfree+0xdc/0x1d4
create_or_delete_synth_event+0x60/0x1e8
trace_parse_run_command+0x2bc/0x4b8
synth_events_write+0x20/0x30
vfs_write+0x200/0x830
...
Allocated by task 4879:
...
kstrdup+0x5c/0x98
create_or_delete_synth_event+0x6c/0x1e8
trace_parse_run_command+0x2bc/0x4b8
synth_events_write+0x20/0x30
vfs_write+0x200/0x830
...
Freed by task 5464:
...
kfree+0xdc/0x1d4
create_or_delete_synth_event+0x60/0x1e8
trace_parse_run_command+0x2bc/0x4b8
synth_events_write+0x20/0x30
vfs_write+0x200/0x830
...
================================================================
Appendix 2. KASAN report use-after-free:
BUG: KASAN: use-after-free in strlen+0x5c/0x7c
Read of size 1 at addr ***** by task sh/5483
sh: CPU: 7 PID: 5483 Comm: sh
...
__asan_report_load1_noabort+0x34/0x44
strlen+0x5c/0x7c
tracing_log_err+0x60/0x444
create_or_delete_synth_event+0xc4/0x204
trace_parse_run_command+0x2bc/0x4b8
synth_events_write+0x20/0x30
vfs_write+0x200/0x830
...
Allocated by task 5483:
...
kstrdup+0x5c/0x98
create_or_delete_synth_event+0x80/0x204
trace_parse_run_command+0x2bc/0x4b8
synth_events_write+0x20/0x30
vfs_write+0x200/0x830
...
Freed by task 5480:
...
kfree+0xdc/0x1d4
create_or_delete_synth_event+0x74/0x204
trace_parse_run_command+0x2bc/0x4b8
synth_events_write+0x20/0x30
vfs_write+0x200/0x830
...
Link: https://lore.kernel.org/linux-trace-kernel/20230321110444.1587-1-Tze-nan.Wu@mediatek.com
Fixes: 27c888da9867 ("tracing: Remove size restriction on synthetic event cmd error logging")
Cc: stable@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Matthias Brugger <matthias.bgg@...il.com>
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Cc: "Tom Zanussi" <zanussi@...nel.org>
Signed-off-by: Tze-nan Wu <Tze-nan.Wu@...iatek.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
kernel/trace/trace_events_synth.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)
diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index 46d0abb32d0f..f0ff730125bf 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -44,14 +44,21 @@ enum { ERRORS };
static const char *err_text[] = { ERRORS };
+DEFINE_MUTEX(lastcmd_mutex);
static char *last_cmd;
static int errpos(const char *str)
{
+ int ret = 0;
+
+ mutex_lock(&lastcmd_mutex);
if (!str || !last_cmd)
- return 0;
+ goto out;
- return err_pos(last_cmd, str);
+ ret = err_pos(last_cmd, str);
+ out:
+ mutex_unlock(&lastcmd_mutex);
+ return ret;
}
static void last_cmd_set(const char *str)
@@ -59,18 +66,22 @@ static void last_cmd_set(const char *str)
if (!str)
return;
+ mutex_lock(&lastcmd_mutex);
kfree(last_cmd);
-
last_cmd = kstrdup(str, GFP_KERNEL);
+ mutex_unlock(&lastcmd_mutex);
}
static void synth_err(u8 err_type, u16 err_pos)
{
+ mutex_lock(&lastcmd_mutex);
if (!last_cmd)
- return;
+ goto out;
tracing_log_err(NULL, "synthetic_events", last_cmd, err_text,
err_type, err_pos);
+ out:
+ mutex_unlock(&lastcmd_mutex);
}
static int create_synth_event(const char *raw_command);
--
2.39.2
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