From nobody Wed Feb 11 13:15:35 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 79187C77B6E for ; Mon, 3 Apr 2023 21:22:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233373AbjDCVWt (ORCPT ); Mon, 3 Apr 2023 17:22:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39364 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232711AbjDCVWq (ORCPT ); Mon, 3 Apr 2023 17:22:46 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3DB623AA0; Mon, 3 Apr 2023 14:22:44 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id CB94B62C05; Mon, 3 Apr 2023 21:22:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 36ACCC433EF; Mon, 3 Apr 2023 21:22:43 +0000 (UTC) Received: from rostedt by gandalf with local (Exim 4.96) (envelope-from ) id 1pjRdS-000FOp-0R; Mon, 03 Apr 2023 17:22:42 -0400 Message-ID: <20230403212241.951576680@goodmis.org> User-Agent: quilt/0.66 Date: Mon, 03 Apr 2023 17:21:26 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Andrew Morton , stable@vger.kernel.org, Matthias Brugger , AngeloGioacchino Del Regno , "Tom Zanussi" , Tze-nan Wu Subject: [for-linus][PATCH 1/6] tracing/synthetic: Fix races on freeing last_cmd References: <20230403212125.244064799@goodmis.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Tze-nan Wu 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. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D 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 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D double-free scenario: process A process B ------------------- --------------- 1.kstrdup last_cmd 2.free last_cmd 3.free last_cmd(double-free) =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D use-after-free scenario: process A process B ------------------- --------------- 1.kstrdup last_cmd 2.free last_cmd 3.tracing_log_err(use-after-free) =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D 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 ... =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D 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 c= md error logging") Cc: stable@vger.kernel.org Cc: Masami Hiramatsu Cc: Matthias Brugger Cc: AngeloGioacchino Del Regno Cc: "Tom Zanussi" Signed-off-by: Tze-nan Wu Signed-off-by: Steven Rostedt (Google) --- 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 }; =20 static const char *err_text[] =3D { ERRORS }; =20 +DEFINE_MUTEX(lastcmd_mutex); static char *last_cmd; =20 static int errpos(const char *str) { + int ret =3D 0; + + mutex_lock(&lastcmd_mutex); if (!str || !last_cmd) - return 0; + goto out; =20 - return err_pos(last_cmd, str); + ret =3D err_pos(last_cmd, str); + out: + mutex_unlock(&lastcmd_mutex); + return ret; } =20 static void last_cmd_set(const char *str) @@ -59,18 +66,22 @@ static void last_cmd_set(const char *str) if (!str) return; =20 + mutex_lock(&lastcmd_mutex); kfree(last_cmd); - last_cmd =3D kstrdup(str, GFP_KERNEL); + mutex_unlock(&lastcmd_mutex); } =20 static void synth_err(u8 err_type, u16 err_pos) { + mutex_lock(&lastcmd_mutex); if (!last_cmd) - return; + goto out; =20 tracing_log_err(NULL, "synthetic_events", last_cmd, err_text, err_type, err_pos); + out: + mutex_unlock(&lastcmd_mutex); } =20 static int create_synth_event(const char *raw_command); --=20 2.39.2