From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752523AbeESOOu (ORCPT ); Sat, 19 May 2018 10:14:50 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:41006 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752506AbeESOOs (ORCPT ); Sat, 19 May 2018 10:14:48 -0400 Date: Sat, 19 May 2018 07:14:45 -0700 From: Matthew Wilcox To: Roman Kagan , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [PATCH] idr: fix invalid ptr dereference on item delete Message-ID: <20180519141445.GA9526@bombadil.infradead.org> References: <20180518175025.GD6361@bombadil.infradead.org> <20180518153138.459c78a83c6bada41b4b187d@linux-foundation.org> <20180519062635.GA6352@rkaganip.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180519062635.GA6352@rkaganip.lan> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, May 19, 2018 at 09:26:36AM +0300, Roman Kagan wrote: > On Fri, May 18, 2018 at 03:31:38PM -0700, Andrew Morton wrote: > > On Fri, 18 May 2018 10:50:25 -0700 Matthew Wilcox wrote: > > > > > If the radix tree underlying the IDR happens to be full and we attempt > > > to remove an id which is larger than any id in the IDR, we will call > > > __radix_tree_delete() with an uninitialised 'slot' pointer, at which > > > point anything could happen. This was easiest to hit with a single entry > > > at id 0 and attempting to remove a non-0 id, but it could have happened > > > with 64 entries and attempting to remove an id >= 64. > > > > > > Fixes: 0a835c4f090a ("Reimplement IDR and IDA using the radix tree") > > > Reported-by: syzbot+35666cba7f0a337e2e79@syzkaller.appspotmail.com > > > Debugged-by: Roman Kagan > > > Signed-off-by: Matthew Wilcox > > > > Neither of the changelogs I'm seeing attempt to describe the end-user > > impact of the bug. People like to know that so they can decide which > > kernel version(s) need patching, so please always remember it. > > That's my fault, Matthew may not have seen the original discussion among > the KVM folks. > > > Looknig at the sysbot report, the impact is at least "privileged user > > can trigger a WARN", but I assume there could be worse, > > Unfortunately it is worse: the syzcaller test boils down to opening > /dev/kvm, creating an eventfd, and calling a couple of KVM ioctls. None > of this requires superuser. And the result is dereferencing an > uninitialized pointer which is likely a crash. > > > as-yet-undiscovered impacts. So I'm thinking a cc:stable is needed, > > yes? > > Well the specific path caught by syzbot is via KVM_HYPERV_EVENTD ioctl > which is new in 4.17. But I guess there are other user-triggerable > paths, so cc:stable is probably justified. We have around 250 calls to idr_remove() in the kernel today. Many of them pass an ID which is embedded in the object they're removing, so they're safe. Picking a few likely candidates: drivers/firewire/core-cdev.c looks unsafe; the ID comes from an ioctl. drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c is similar drivers/atm/nicstar.c could be taken down by a handcrafted packet