From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 847FEC43461 for ; Mon, 7 Sep 2020 11:31:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4E7BF21481 for ; Mon, 7 Sep 2020 11:31:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728779AbgIGLbQ (ORCPT ); Mon, 7 Sep 2020 07:31:16 -0400 Received: from mga07.intel.com ([134.134.136.100]:14653 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728913AbgIGLY6 (ORCPT ); Mon, 7 Sep 2020 07:24:58 -0400 IronPort-SDR: wwd0a+z9M75QE6cjLp5ZXtBLRm9ILwtaQVtT1vMKEPMXPK5dQ+6LMcNa+H0drDelarUCsAEXhr zXTcePAcDz5g== X-IronPort-AV: E=McAfee;i="6000,8403,9736"; a="222196737" X-IronPort-AV: E=Sophos;i="5.76,401,1592895600"; d="scan'208";a="222196737" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Sep 2020 04:05:47 -0700 IronPort-SDR: /v5b++m3kkkbfFA9wbim3ZJdffEEVpxjZhqPtTvjdgKUi4hmW4iO8F388Pcbzls2iqus21xquf ByBivjDzRdqQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.76,401,1592895600"; d="scan'208";a="303700090" Received: from stinkbox.fi.intel.com (HELO stinkbox) ([10.237.72.174]) by orsmga006.jf.intel.com with SMTP; 07 Sep 2020 04:05:45 -0700 Received: by stinkbox (sSMTP sendmail emulation); Mon, 07 Sep 2020 14:05:44 +0300 Date: Mon, 7 Sep 2020 14:05:44 +0300 From: Ville =?iso-8859-1?Q?Syrj=E4l=E4?= To: Zwane Mwaikambo Cc: Lyude Paul , dri-devel , zwanem@gmail.com, dkwon@redhat.com, Linux Kernel Subject: Re: [PATCH]] drm/dp check aux_dev before use in drm_dp_aux_dev_get_by_minor() Message-ID: <20200907110544.GE6112@intel.com> References: <20200811085830.GZ2352366@phenom.ffwll.local> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Patchwork-Hint: comment User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 04, 2020 at 12:21:26AM -0700, Zwane Mwaikambo wrote: > I observed this when unplugging a DP monitor whilst a computer is asleep > and then waking it up. This left DP chardev nodes still being present on > the filesystem and accessing these device nodes caused an oops because > drm_dp_aux_dev_get_by_minor() assumes a device exists if it is opened. > This can also be reproduced by creating a device node with mknod(1) and > issuing an open(2) > > [166164.933198] BUG: kernel NULL pointer dereference, address: 0000000000000018 > [166164.933202] #PF: supervisor read access in kernel mode > [166164.933204] #PF: error_code(0x0000) - not-present page > [166164.933205] PGD 0 P4D 0 > [166164.933208] Oops: 0000 [#1] PREEMPT SMP NOPTI > [166164.933211] CPU: 4 PID: 99071 Comm: fwupd Tainted: G W > 5.8.0-rc6+ #1 > [166164.933213] Hardware name: LENOVO 20RD002VUS/20RD002VUS, BIOS R16ET25W > (1.11 ) 04/21/2020 > [166164.933232] RIP: 0010:drm_dp_aux_dev_get_by_minor+0x29/0x70 > [drm_kms_helper] > [166164.933234] Code: 00 0f 1f 44 00 00 55 48 89 e5 41 54 41 89 fc 48 c7 > c7 60 01 a4 c0 e8 26 ab 30 d7 44 89 e6 48 c7 c7 80 01 a4 c0 e8 47 94 d6 d6 > <8b> 50 18 49 89 c4 48 8d 78 18 85 d2 74 33 8d 4a 01 89 d0 f0 0f b1 > [166164.933236] RSP: 0018:ffffb7d7c41cbbf0 EFLAGS: 00010246 > [166164.933237] RAX: 0000000000000000 RBX: ffff8a90001fe900 RCX: 0000000000000000 > [166164.933238] RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffffffffc0a40180 > [166164.933239] RBP: ffffb7d7c41cbbf8 R08: 0000000000000000 R09: ffff8a93e157d6d0 > [166164.933240] R10: 0000000000000000 R11: ffffffffc0a40188 R12: 0000000000000003 > [166164.933241] R13: ffff8a9402200e80 R14: ffff8a90001fe900 R15: 0000000000000000 > [166164.933244] FS: 00007f7fb041eb00(0000) GS:ffff8a9411500000(0000) > knlGS:0000000000000000 > [166164.933245] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [166164.933246] CR2: 0000000000000018 CR3: 00000000352c2003 CR4: 00000000003606e0 > [166164.933247] Call Trace: > [166164.933264] auxdev_open+0x1b/0x40 [drm_kms_helper] > [166164.933278] chrdev_open+0xa7/0x1c0 > [166164.933282] ? cdev_put.part.0+0x20/0x20 > [166164.933287] do_dentry_open+0x161/0x3c0 > [166164.933291] vfs_open+0x2d/0x30 > [166164.933297] path_openat+0xb27/0x10e0 > [166164.933306] ? atime_needs_update+0x73/0xd0 > [166164.933309] do_filp_open+0x91/0x100 > [166164.933313] ? __alloc_fd+0xb2/0x150 > [166164.933316] do_sys_openat2+0x210/0x2d0 > [166164.933318] do_sys_open+0x46/0x80 > [166164.933320] __x64_sys_openat+0x20/0x30 > [166164.933328] do_syscall_64+0x52/0xc0 > [166164.933336] entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > > (gdb) disassemble drm_dp_aux_dev_get_by_minor+0x29 > Dump of assembler code for function drm_dp_aux_dev_get_by_minor: > 0x0000000000017b10 <+0>: callq 0x17b15 > 0x0000000000017b15 <+5>: push %rbp > 0x0000000000017b16 <+6>: mov %rsp,%rbp > 0x0000000000017b19 <+9>: push %r12 > 0x0000000000017b1b <+11>: mov %edi,%r12d > 0x0000000000017b1e <+14>: mov $0x0,%rdi > 0x0000000000017b25 <+21>: callq 0x17b2a > 0x0000000000017b2a <+26>: mov %r12d,%esi > 0x0000000000017b2d <+29>: mov $0x0,%rdi > 0x0000000000017b34 <+36>: callq 0x17b39 > 0x0000000000017b39 <+41>: mov 0x18(%rax),%edx <========= > 0x0000000000017b3c <+44>: mov %rax,%r12 > 0x0000000000017b3f <+47>: lea 0x18(%rax),%rdi > 0x0000000000017b43 <+51>: test %edx,%edx > 0x0000000000017b45 <+53>: je 0x17b7a > 0x0000000000017b47 <+55>: lea 0x1(%rdx),%ecx > 0x0000000000017b4a <+58>: mov %edx,%eax > 0x0000000000017b4c <+60>: lock cmpxchg %ecx,(%rdi) > 0x0000000000017b50 <+64>: jne 0x17b76 > 0x0000000000017b52 <+66>: test %edx,%edx > 0x0000000000017b54 <+68>: js 0x17b6d > 0x0000000000017b56 <+70>: test %ecx,%ecx > 0x0000000000017b58 <+72>: js 0x17b6d > 0x0000000000017b5a <+74>: mov $0x0,%rdi > 0x0000000000017b61 <+81>: callq 0x17b66 > 0x0000000000017b66 <+86>: mov %r12,%rax > 0x0000000000017b69 <+89>: pop %r12 > 0x0000000000017b6b <+91>: pop %rbp > 0x0000000000017b6c <+92>: retq > 0x0000000000017b6d <+93>: xor %esi,%esi > 0x0000000000017b6f <+95>: callq 0x17b74 > 0x0000000000017b74 <+100>: jmp 0x17b5a > 0x0000000000017b76 <+102>: mov %eax,%edx > 0x0000000000017b78 <+104>: jmp 0x17b43 > 0x0000000000017b7a <+106>: xor %r12d,%r12d > 0x0000000000017b7d <+109>: jmp 0x17b5a > End of assembler dump. > > (gdb) list *drm_dp_aux_dev_get_by_minor+0x29 > 0x17b39 is in drm_dp_aux_dev_get_by_minor (drivers/gpu/drm/drm_dp_aux_dev.c:65). > 60 static struct drm_dp_aux_dev *drm_dp_aux_dev_get_by_minor(unsigned index) > 61 { > 62 struct drm_dp_aux_dev *aux_dev = NULL; > 63 > 64 mutex_lock(&aux_idr_mutex); > 65 aux_dev = idr_find(&aux_idr, index); > 66 if (!kref_get_unless_zero(&aux_dev->refcount)) > 67 aux_dev = NULL; > 68 mutex_unlock(&aux_idr_mutex); > 69 > (gdb) p/x &((struct drm_dp_aux_dev *)(0x0))->refcount > $8 = 0x18 > > Looking at the caller, checks on the minor are pushed down to > drm_dp_aux_dev_get_by_minor() > > static int auxdev_open(struct inode *inode, struct file *file) > { > unsigned int minor = iminor(inode); > struct drm_dp_aux_dev *aux_dev; > > aux_dev = drm_dp_aux_dev_get_by_minor(minor); <==== > if (!aux_dev) > return -ENODEV; > > file->private_data = aux_dev; > return 0; > } > > > Fixes: e94cb37b34eb8 ("Add a drm_aux-dev module for reading/writing dpcd registers") > Cc: stable@vger.kernel.org > Signed-off-by: Zwane Mwaikambo > --- > > diff --git a/drivers/gpu/drm/drm_dp_aux_dev.c b/drivers/gpu/drm/drm_dp_aux_dev.c > index 2510717d5a08..e25181bf2c48 100644 > --- a/drivers/gpu/drm/drm_dp_aux_dev.c > +++ b/drivers/gpu/drm/drm_dp_aux_dev.c > @@ -63,7 +63,7 @@ static struct drm_dp_aux_dev *drm_dp_aux_dev_get_by_minor(unsigned index) > > mutex_lock(&aux_idr_mutex); > aux_dev = idr_find(&aux_idr, index); > - if (!kref_get_unless_zero(&aux_dev->refcount)) > + if (aux_dev && !kref_get_unless_zero(&aux_dev->refcount)) Dejavu https://lists.freedesktop.org/archives/dri-devel/2019-May/218855.html https://lists.freedesktop.org/archives/dri-devel/2019-July/226168.html I guess we just got stuck waiting for confirmation that it reproduces with the bogus device node trick. > aux_dev = NULL; > mutex_unlock(&aux_idr_mutex); > > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel -- Ville Syrjälä Intel