From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id 752028E00AE for ; Thu, 3 Jan 2019 15:32:01 -0500 (EST) Received: by mail-ed1-f71.google.com with SMTP id m19so34236489edc.6 for ; Thu, 03 Jan 2019 12:32:01 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id r24si2932543edp.187.2019.01.03.12.31.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 03 Jan 2019 12:31:59 -0800 (PST) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Thu, 03 Jan 2019 21:31:58 +0100 From: Roman Penyaev Subject: Re: [PATCH 1/3] mm/vmalloc: fix size check for remap_vmalloc_range_partial() In-Reply-To: <20190103194054.GB31793@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> Message-ID: <5502b64d6c508f5432386d2cfe999844@suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrew Morton , Andrey Ryabinin , Joe Perches , "Luis R." Rodriguez" , linux-mm@kvack.org," linux-kernel@vger.kernel.org, stable@vger.kernel.org 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); According to the code no explicit size check, should be easy to reproduce: mmap the frame buffer and you are done. Other callers are not so easy to follow. But wait, here is another example: (drivers/video/fbdev/core/fbmem.c) static int fb_mmap(struct file *file, struct vm_area_struct * vma) ... res = fb->fb_mmap(info, vma); (drivers/video/fbdev/vfb.c) static int vfb_mmap(struct fb_info *info, struct vm_area_struct *vma) { return remap_vmalloc_range(vma, (void *)info->fix.smem_start, vma->vm_pgoff); } No checks, naked calls, should be also the candidate. -- Roman