From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 7FDD58E00AE for ; Fri, 4 Jan 2019 04:38:12 -0500 (EST) Received: by mail-ed1-f70.google.com with SMTP id s50so34703305edd.11 for ; Fri, 04 Jan 2019 01:38:12 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id gl12-v6si6081527ejb.145.2019.01.04.01.38.10 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 04 Jan 2019 01:38:10 -0800 (PST) Date: Fri, 4 Jan 2019 10:38:08 +0100 From: Michal Hocko Subject: Re: [PATCH 1/3] mm/vmalloc: fix size check for remap_vmalloc_range_partial() Message-ID: <20190104093808.GJ31793@dhcp22.suse.cz> References: <20190103145954.16942-1-rpenyaev@suse.de> <20190103145954.16942-2-rpenyaev@suse.de> <20190103151357.GR31793@dhcp22.suse.cz> <20190103194054.GB31793@dhcp22.suse.cz> <5502b64d6c508f5432386d2cfe999844@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5502b64d6c508f5432386d2cfe999844@suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Roman Penyaev Cc: Andrew Morton , Andrey Ryabinin , Joe Perches , "Luis R. Rodriguez" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org On Thu 03-01-19 21:31:58, Roman Penyaev wrote: > On 2019-01-03 20:40, Michal Hocko wrote: > > On Thu 03-01-19 20:27:26, Roman Penyaev wrote: > > > On 2019-01-03 16:13, Michal Hocko wrote: > > > > On Thu 03-01-19 15:59:52, Roman Penyaev wrote: > > > > > area->size can include adjacent guard page but get_vm_area_size() > > > > > returns actual size of the area. > > > > > > > > > > This fixes possible kernel crash when userspace tries to map area > > > > > on 1 page bigger: size check passes but the following > > > > > vmalloc_to_page() > > > > > returns NULL on last guard (non-existing) page. > > > > > > > > Can this actually happen? I am not really familiar with all the callers > > > > of this API but VM_NO_GUARD is not really used wildly in the kernel. > > > > > > Exactly, by default (VM_NO_GUARD is not set) each area has guard page, > > > thus the area->size will be bigger. The bug is not reproduced if > > > VM_NO_GUARD is set. > > > > > > > All I can see is kasan na arm64 which doesn't really seem to use it > > > > for vmalloc. > > > > > > > > So is the problem real or this is a mere cleanup? > > > > > > This is the real problem, try this hunk for any file descriptor which > > > provides > > > mapping, or say modify epoll as example: > > > > OK, my response was more confusing than I intended. I meant to say. Is > > there any in kernel code that would allow the bug have had in mind? > > In other words can userspace trick any existing code? > > In theory any existing caller of remap_vmalloc_range() which does > not have an explicit size check should trigger an oops, e.g. this is > a good candidate: > > *** drivers/media/usb/stkwebcam/stk-webcam.c: > v4l_stk_mmap[789] ret = remap_vmalloc_range(vma, sbuf->buffer, > 0); Hmm, sbuf->buffer is allocated in stk_setup_siobuf to have buf->v4lbuf.length. mmap callback maps this buffer to the vma size and that is indeed not enforced to be <= length AFAICS. So you are right! Can we have an example in the changelog please? Thanks! -- Michal Hocko SUSE Labs