From nobody Wed Apr 8 12:35:02 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 B97CFC25B08 for ; Sun, 21 Aug 2022 00:09:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236556AbiHUAJI (ORCPT ); Sat, 20 Aug 2022 20:09:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41076 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235646AbiHUAIg (ORCPT ); Sat, 20 Aug 2022 20:08:36 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2CB5F11C11 for ; Sat, 20 Aug 2022 17:08:33 -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 ams.source.kernel.org (Postfix) with ESMTPS id D35CBB80B69 for ; Sun, 21 Aug 2022 00:08:31 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 89242C43141; Sun, 21 Aug 2022 00:08:30 +0000 (UTC) Received: from rostedt by gandalf.local.home with local (Exim 4.96) (envelope-from ) id 1oPYWD-005DlX-0f; Sat, 20 Aug 2022 20:08:45 -0400 Message-ID: <20220821000845.047156494@goodmis.org> User-Agent: quilt/0.66 Date: Sat, 20 Aug 2022 20:07:41 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Ingo Molnar , Andrew Morton , Yang Jihong Subject: [for-linus][PATCH 04/10] ftrace: Fix NULL pointer dereference in is_ftrace_trampoline when ftrace is dead References: <20220821000737.328590235@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: Yang Jihong ftrace_startup does not remove ops from ftrace_ops_list when ftrace_startup_enable fails: register_ftrace_function ftrace_startup __register_ftrace_function ... add_ftrace_ops(&ftrace_ops_list, ops) ... ... ftrace_startup_enable // if ftrace failed to modify, ftrace_disabled is= set to 1 ... return 0 // ops is in the ftrace_ops_list. When ftrace_disabled =3D 1, unregister_ftrace_function simply returns witho= ut doing anything: unregister_ftrace_function ftrace_shutdown if (unlikely(ftrace_disabled)) return -ENODEV; // return here, __unregister_ftrace_function i= s not executed, // as a result, ops is still in the ftrace_ops= _list __unregister_ftrace_function ... If ops is dynamically allocated, it will be free later, in this case, is_ftrace_trampoline accesses NULL pointer: is_ftrace_trampoline ftrace_ops_trampoline do_for_each_ftrace_op(op, ftrace_ops_list) // OOPS! op may be NULL! Syzkaller reports as follows: [ 1203.506103] BUG: kernel NULL pointer dereference, address: 0000000000000= 10b [ 1203.508039] #PF: supervisor read access in kernel mode [ 1203.508798] #PF: error_code(0x0000) - not-present page [ 1203.509558] PGD 800000011660b067 P4D 800000011660b067 PUD 130fb8067 PMD 0 [ 1203.510560] Oops: 0000 [#1] SMP KASAN PTI [ 1203.511189] CPU: 6 PID: 29532 Comm: syz-executor.2 Tainted: G B W = 5.10.0 #8 [ 1203.512324] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS = rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014 [ 1203.513895] RIP: 0010:is_ftrace_trampoline+0x26/0xb0 [ 1203.514644] Code: ff eb d3 90 41 55 41 54 49 89 fc 55 53 e8 f2 00 fd ff = 48 8b 1d 3b 35 5d 03 e8 e6 00 fd ff 48 8d bb 90 00 00 00 e8 2a 81 26 00 <48= > 8b ab 90 00 00 00 48 85 ed 74 1d e8 c9 00 fd ff 48 8d bb 98 00 [ 1203.518838] RSP: 0018:ffffc900012cf960 EFLAGS: 00010246 [ 1203.520092] RAX: 0000000000000000 RBX: 000000000000007b RCX: ffffffff8a3= 31866 [ 1203.521469] RDX: 0000000000000000 RSI: 0000000000000008 RDI: 00000000000= 0010b [ 1203.522583] RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff8df= 18b07 [ 1203.523550] R10: fffffbfff1be3160 R11: 0000000000000001 R12: 00000000004= 78399 [ 1203.524596] R13: 0000000000000000 R14: ffff888145088000 R15: 00000000000= 00008 [ 1203.525634] FS: 00007f429f5f4700(0000) GS:ffff8881daf00000(0000) knlGS:= 0000000000000000 [ 1203.526801] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 1203.527626] CR2: 000000000000010b CR3: 0000000170e1e001 CR4: 00000000003= 706e0 [ 1203.528611] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 00000000000= 00000 [ 1203.529605] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 00000000000= 00400 Therefore, when ftrace_startup_enable fails, we need to rollback registrati= on process and remove ops from ftrace_ops_list. Link: https://lkml.kernel.org/r/20220818032659.56209-1-yangjihong1@huawei.c= om Suggested-by: Steven Rostedt Signed-off-by: Yang Jihong Signed-off-by: Steven Rostedt (Google) --- kernel/trace/ftrace.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 601ccf1b2f09..4baa99363b16 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -2937,6 +2937,16 @@ int ftrace_startup(struct ftrace_ops *ops, int comma= nd) =20 ftrace_startup_enable(command); =20 + /* + * If ftrace is in an undefined state, we just remove ops from list + * to prevent the NULL pointer, instead of totally rolling it back and + * free trampoline, because those actions could cause further damage. + */ + if (unlikely(ftrace_disabled)) { + __unregister_ftrace_function(ops); + return -ENODEV; + } + ops->flags &=3D ~FTRACE_OPS_FL_ADDING; =20 return 0; --=20 2.35.1