From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965156AbeBMPDN (ORCPT ); Tue, 13 Feb 2018 10:03:13 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:60444 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S965037AbeBMPDM (ORCPT ); Tue, 13 Feb 2018 10:03:12 -0500 Subject: Re: [patch] kvm: suppress KVM_SET_GSI_ROUTING allocation failure To: Michal Hocko , David Rientjes Cc: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <20180213144836.GU3443@dhcp22.suse.cz> From: Paolo Bonzini Message-ID: Date: Tue, 13 Feb 2018 16:03:09 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 MIME-Version: 1.0 In-Reply-To: <20180213144836.GU3443@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13/02/2018 15:48, Michal Hocko wrote: > On Thu 08-02-18 13:35:08, David Rientjes wrote: >> The KVM_SET_GSI_ROUTING ioctl does a vmalloc() of >> sizeof(struct kvm_irq_routing_entry) multiplied by a user-supplied value. >> This can be up to 4096 entries on architectures such as arm64 and s390 >> (and the upper bound may be increased on s390 eventually). >> >> This can produce a vmalloc allocation failure warning: >> >> vmalloc: allocation failure: 0 bytes, mode:0x24000c2(GFP_KERNEL|__GFP_HIGHMEM) > > I am not arguing about the kvm change but do we actaully want to warn > for 0 sized allocations? This just doesn't make much sense to me. > In other words don't we want this? > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 673942094328..c5d832510c54 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -1748,7 +1748,9 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align, > unsigned long real_size = size; > > size = PAGE_ALIGN(size); > - if (!size || (size >> PAGE_SHIFT) > totalram_pages) > + if (!size) > + return NULL; > + if ((size >> PAGE_SHIFT) > totalram_pages) > goto fail; > > area = __get_vm_area_node(size, align, VM_ALLOC | VM_UNINITIALIZED | > There have been quite a few reports of this from syzkaller and generally we've fixed them. It does seem like a recipe for NULL-pointer dereferences when the size is user-controlled (as in this case). But here I'm actually not sure that the "allocation failure: 0 bytes" can happen, since we have a check above for "if (routing.nr)", and there is a check also so that the maximum allocation here is a meager 128 KiB. So I'm wondering if this patch is obsolete actually after commit f8c1b85b2523. David? Thanks, Paolo Paolo