From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrea Righi Subject: Re: [PATCH] fbdev: potential information leak in do_fb_ioctl() Date: Wed, 30 Oct 2019 21:12:01 +0100 Message-ID: <20191030201201.GA3209@xps-13> References: <20191029182320.GA17569@mwanda> <87zhhjjryk.fsf@x220.int.ebiederm.org> <20191030074321.GD2656@xps-13> <87r22ujaqq.fsf@x220.int.ebiederm.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <87r22ujaqq.fsf@x220.int.ebiederm.org> Sender: linux-kernel-owner@vger.kernel.org To: "Eric W. Biederman" Cc: Dan Carpenter , Bartlomiej Zolnierkiewicz , Daniel Vetter , Sam Ravnborg , Maarten Lankhorst , Peter Rosin , Gerd Hoffmann , dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org, security@kernel.org, Kees Cook , Julia Lawall List-Id: dri-devel@lists.freedesktop.org On Wed, Oct 30, 2019 at 02:26:21PM -0500, Eric W. Biederman wrote: > Andrea Righi writes: > > > On Tue, Oct 29, 2019 at 02:02:11PM -0500, Eric W. Biederman wrote: > >> Dan Carpenter writes: > >> > >> > The "fix" struct has a 2 byte hole after ->ywrapstep and the > >> > "fix = info->fix;" assignment doesn't necessarily clear it. It depends > >> > on the compiler. > >> > > >> > Fixes: 1f5e31d7e55a ("fbmem: don't call copy_from/to_user() with mutex held") > >> > Signed-off-by: Dan Carpenter > >> > --- > >> > I have 13 more similar places to patch... I'm not totally sure I > >> > understand all the issues involved. > >> > >> What I have done in a similar situation with struct siginfo, is that > >> where the structure first appears I have initialized it with memset, > >> and then field by field. > >> > >> Then when the structure is copied I copy the structure with memcpy. > >> > >> That ensures all of the bytes in the original structure are initialized > >> and that all of the bytes are copied. > >> > >> The goal is to avoid memory that has values of the previous users of > >> that memory region from leaking to userspace. Which depending on who > >> the previous user of that memory region is could tell userspace > >> information about what the kernel is doing that it should not be allowed > >> to find out. > >> > >> I tried to trace through where "info" and thus presumably "info->fix" is > >> coming from and only made it as far as register_framebuffer. Given > >> that I suspect a local memset, and then a field by field copy right > >> before copy_to_user might be a sound solution. But ick. That is a lot > >> of fields to copy. > > > > I know it might sound quite inefficient, but what about making struct > > fb_fix_screeninfo __packed? > > > > This doesn't solve other potential similar issues, but for this > > particular case it could be a reasonable and simple fix. > > It is part of the user space ABI. As such you can't move the fields. > > Eric Oh, that's right! Then memset() + memcpy() is probably the best option, since copying all those fields one by one looks quite ugly to me... -Andrea 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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 C3E51CA9EC3 for ; Thu, 31 Oct 2019 09:05:08 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A2E862083E for ; Thu, 31 Oct 2019 09:05:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A2E862083E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=canonical.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id DFC666EDDF; Thu, 31 Oct 2019 09:04:24 +0000 (UTC) Received: from youngberry.canonical.com (youngberry.canonical.com [91.189.89.112]) by gabe.freedesktop.org (Postfix) with ESMTPS id 8C3F26EAB7 for ; Wed, 30 Oct 2019 20:12:05 +0000 (UTC) Received: from mail-wr1-f69.google.com ([209.85.221.69]) by youngberry.canonical.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1iPuK3-00049Q-VM for dri-devel@lists.freedesktop.org; Wed, 30 Oct 2019 20:12:03 +0000 Received: by mail-wr1-f69.google.com with SMTP id f4so1948499wrj.12 for ; Wed, 30 Oct 2019 13:12:03 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=AVK3dTX5VeGMLnBzR7G4n82XaLQo9FRcTOWzPDhXKnM=; b=MwOItp8s0GuDFHP96whQGn8NP/qLDS/50JfqaENtFQDEUblNizHnb3l2wVziCtZUeu 5UNl9r0qtT9fkDcuU3FcmdvR77YGHeVL4vb2BbwnHwwQ7kUmzWUylwCVMHyXr3J9tJ1i vtMQ7VwfTRFeesvT2M7RjQTORvuw252/A44ybh4VsPcXMe0ypldzVgWyTOHmVS2vd2V0 g+MGNuRlM/Ww0Tq22YCCp7tnrPFtjBIjgBwZc9v/o21wtj+RkSMBVBDE91R9BT31osPE 1q9dF6sd6aNwMQ7fBZbb85F1Weeu2aX/+tbJYuCjRfGYZ4spG0BVNzs2CrQylqdTs3fD jNsg== X-Gm-Message-State: APjAAAV4r4NSTgWsvF4gSe0U18nwuSoqjHUQ51G+7I/3/Yj0Wmxfjl+D 3I95bADQ5QuxDVEuw7da6fpxfThsiFN3VKBRcrBzEqKOJKLBrLt27T9f2fb4Ceu4GzwEkjlXEGA /109SjDwvVEN6qQCAebpiFTl5ROkUzVEfScjyc2kZgKw9NA== X-Received: by 2002:a5d:678e:: with SMTP id v14mr1517130wru.393.1572466323595; Wed, 30 Oct 2019 13:12:03 -0700 (PDT) X-Google-Smtp-Source: APXvYqxlH3NbfJNwZ+iH3vOzPj9s1eHdaXQjgrBiVlMVrAzQAGIq2J05NZ48ryoa5j1osqZbWvhIHw== X-Received: by 2002:a5d:678e:: with SMTP id v14mr1517106wru.393.1572466323277; Wed, 30 Oct 2019 13:12:03 -0700 (PDT) Received: from localhost ([178.18.58.186]) by smtp.gmail.com with ESMTPSA id j22sm1733453wrd.41.2019.10.30.13.12.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Oct 2019 13:12:02 -0700 (PDT) Date: Wed, 30 Oct 2019 21:12:01 +0100 From: Andrea Righi To: "Eric W. Biederman" Subject: Re: [PATCH] fbdev: potential information leak in do_fb_ioctl() Message-ID: <20191030201201.GA3209@xps-13> References: <20191029182320.GA17569@mwanda> <87zhhjjryk.fsf@x220.int.ebiederm.org> <20191030074321.GD2656@xps-13> <87r22ujaqq.fsf@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <87r22ujaqq.fsf@x220.int.ebiederm.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-Mailman-Approved-At: Thu, 31 Oct 2019 09:04:21 +0000 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-fbdev@vger.kernel.org, security@kernel.org, Kees Cook , Bartlomiej Zolnierkiewicz , kernel-janitors@vger.kernel.org, Daniel Vetter , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Julia Lawall , Gerd Hoffmann , Sam Ravnborg , Peter Rosin , Dan Carpenter Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Message-ID: <20191030201201.GEB64xqD3u8lszaQrdnBxFJwk9T41hqskvDl2WL2YA8@z> T24gV2VkLCBPY3QgMzAsIDIwMTkgYXQgMDI6MjY6MjFQTSAtMDUwMCwgRXJpYyBXLiBCaWVkZXJt YW4gd3JvdGU6Cj4gQW5kcmVhIFJpZ2hpIDxhbmRyZWEucmlnaGlAY2Fub25pY2FsLmNvbT4gd3Jp dGVzOgo+IAo+ID4gT24gVHVlLCBPY3QgMjksIDIwMTkgYXQgMDI6MDI6MTFQTSAtMDUwMCwgRXJp YyBXLiBCaWVkZXJtYW4gd3JvdGU6Cj4gPj4gRGFuIENhcnBlbnRlciA8ZGFuLmNhcnBlbnRlckBv cmFjbGUuY29tPiB3cml0ZXM6Cj4gPj4gCj4gPj4gPiBUaGUgImZpeCIgc3RydWN0IGhhcyBhIDIg Ynl0ZSBob2xlIGFmdGVyIC0+eXdyYXBzdGVwIGFuZCB0aGUKPiA+PiA+ICJmaXggPSBpbmZvLT5m aXg7IiBhc3NpZ25tZW50IGRvZXNuJ3QgbmVjZXNzYXJpbHkgY2xlYXIgaXQuICBJdCBkZXBlbmRz Cj4gPj4gPiBvbiB0aGUgY29tcGlsZXIuCj4gPj4gPgo+ID4+ID4gRml4ZXM6IDFmNWUzMWQ3ZTU1 YSAoImZibWVtOiBkb24ndCBjYWxsIGNvcHlfZnJvbS90b191c2VyKCkgd2l0aCBtdXRleCBoZWxk IikKPiA+PiA+IFNpZ25lZC1vZmYtYnk6IERhbiBDYXJwZW50ZXIgPGRhbi5jYXJwZW50ZXJAb3Jh Y2xlLmNvbT4KPiA+PiA+IC0tLQo+ID4+ID4gSSBoYXZlIDEzIG1vcmUgc2ltaWxhciBwbGFjZXMg dG8gcGF0Y2guLi4gIEknbSBub3QgdG90YWxseSBzdXJlIEkKPiA+PiA+IHVuZGVyc3RhbmQgYWxs IHRoZSBpc3N1ZXMgaW52b2x2ZWQuCj4gPj4gCj4gPj4gV2hhdCBJIGhhdmUgZG9uZSBpbiBhIHNp bWlsYXIgc2l0dWF0aW9uIHdpdGggc3RydWN0IHNpZ2luZm8sIGlzIHRoYXQKPiA+PiB3aGVyZSB0 aGUgc3RydWN0dXJlIGZpcnN0IGFwcGVhcnMgSSBoYXZlIGluaXRpYWxpemVkIGl0IHdpdGggbWVt c2V0LAo+ID4+IGFuZCB0aGVuIGZpZWxkIGJ5IGZpZWxkLgo+ID4+IAo+ID4+IFRoZW4gd2hlbiB0 aGUgc3RydWN0dXJlIGlzIGNvcGllZCBJIGNvcHkgdGhlIHN0cnVjdHVyZSB3aXRoIG1lbWNweS4K PiA+PiAKPiA+PiBUaGF0IGVuc3VyZXMgYWxsIG9mIHRoZSBieXRlcyBpbiB0aGUgb3JpZ2luYWwg c3RydWN0dXJlIGFyZSBpbml0aWFsaXplZAo+ID4+IGFuZCB0aGF0IGFsbCBvZiB0aGUgYnl0ZXMg YXJlIGNvcGllZC4KPiA+PiAKPiA+PiBUaGUgZ29hbCBpcyB0byBhdm9pZCBtZW1vcnkgdGhhdCBo YXMgdmFsdWVzIG9mIHRoZSBwcmV2aW91cyB1c2VycyBvZgo+ID4+IHRoYXQgbWVtb3J5IHJlZ2lv biBmcm9tIGxlYWtpbmcgdG8gdXNlcnNwYWNlLiAgV2hpY2ggZGVwZW5kaW5nIG9uIHdobwo+ID4+ IHRoZSBwcmV2aW91cyB1c2VyIG9mIHRoYXQgbWVtb3J5IHJlZ2lvbiBpcyBjb3VsZCB0ZWxsIHVz ZXJzcGFjZQo+ID4+IGluZm9ybWF0aW9uIGFib3V0IHdoYXQgdGhlIGtlcm5lbCBpcyBkb2luZyB0 aGF0IGl0IHNob3VsZCBub3QgYmUgYWxsb3dlZAo+ID4+IHRvIGZpbmQgb3V0Lgo+ID4+IAo+ID4+ IEkgdHJpZWQgdG8gdHJhY2UgdGhyb3VnaCB3aGVyZSAiaW5mbyIgYW5kIHRodXMgcHJlc3VtYWJs eSAiaW5mby0+Zml4IiBpcwo+ID4+IGNvbWluZyBmcm9tIGFuZCBvbmx5IG1hZGUgaXQgYXMgZmFy IGFzICByZWdpc3Rlcl9mcmFtZWJ1ZmZlci4gIEdpdmVuCj4gPj4gdGhhdCBJIHN1c3BlY3QgYSBs b2NhbCBtZW1zZXQsIGFuZCB0aGVuIGEgZmllbGQgYnkgZmllbGQgY29weSByaWdodAo+ID4+IGJl Zm9yZSBjb3B5X3RvX3VzZXIgbWlnaHQgYmUgYSBzb3VuZCBzb2x1dGlvbi4gIEJ1dCBpY2suICBU aGF0IGlzIGEgbG90Cj4gPj4gb2YgZmllbGRzIHRvIGNvcHkuCj4gPgo+ID4gSSBrbm93IGl0IG1p Z2h0IHNvdW5kIHF1aXRlIGluZWZmaWNpZW50LCBidXQgd2hhdCBhYm91dCBtYWtpbmcgc3RydWN0 Cj4gPiBmYl9maXhfc2NyZWVuaW5mbyBfX3BhY2tlZD8KPiA+Cj4gPiBUaGlzIGRvZXNuJ3Qgc29s dmUgb3RoZXIgcG90ZW50aWFsIHNpbWlsYXIgaXNzdWVzLCBidXQgZm9yIHRoaXMKPiA+IHBhcnRp Y3VsYXIgY2FzZSBpdCBjb3VsZCBiZSBhIHJlYXNvbmFibGUgYW5kIHNpbXBsZSBmaXguCj4gCj4g SXQgaXMgcGFydCBvZiB0aGUgdXNlciBzcGFjZSBBQkkuICBBcyBzdWNoIHlvdSBjYW4ndCBtb3Zl IHRoZSBmaWVsZHMuCj4gCj4gRXJpYwoKT2gsIHRoYXQncyByaWdodCEgVGhlbiBtZW1zZXQoKSAr IG1lbWNweSgpIGlzIHByb2JhYmx5IHRoZSBiZXN0IG9wdGlvbiwKc2luY2UgY29weWluZyBhbGwg dGhvc2UgZmllbGRzIG9uZSBieSBvbmUgbG9va3MgcXVpdGUgdWdseSB0byBtZS4uLgoKLUFuZHJl YQpfX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fXwpkcmktZGV2 ZWwgbWFpbGluZyBsaXN0CmRyaS1kZXZlbEBsaXN0cy5mcmVlZGVza3RvcC5vcmcKaHR0cHM6Ly9s aXN0cy5mcmVlZGVza3RvcC5vcmcvbWFpbG1hbi9saXN0aW5mby9kcmktZGV2ZWw=