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=-2.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 01083C433ED for ; Fri, 23 Apr 2021 05:11:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C152761164 for ; Fri, 23 Apr 2021 05:11:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231523AbhDWFMK (ORCPT ); Fri, 23 Apr 2021 01:12:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60648 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229456AbhDWFMK (ORCPT ); Fri, 23 Apr 2021 01:12:10 -0400 Received: from mail-lf1-x12d.google.com (mail-lf1-x12d.google.com [IPv6:2a00:1450:4864:20::12d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 22635C061574; Thu, 22 Apr 2021 22:11:33 -0700 (PDT) Received: by mail-lf1-x12d.google.com with SMTP id d27so18779518lfv.9; Thu, 22 Apr 2021 22:11:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=fIRfzDU/CpJ2GwUwi5qaYyALcM0b/ZoofzJjBH1j+y0=; b=pofHhJn5Dbu9gmZ8D0IkPEuxaxfysZnusWgwpk5zuMzElVg5ywpEIYE0dcmAtSQJSB X4AxLNumat7hlUCquX+K+3KzFDUyveGLsH25BaXqPDk6aSl30k2A68QdCYayI3M7+pZR yyEEdWmRpN9F8x2EQhwuxix0JEkDsuD10hVbitcElO9PlpVJs8ohdxMtcZ+ZnV766wWs yEa62gxxAG9z+nPS/PLtBF9yWfWdPFvhK3JVCvCQjO+OPFAIAMgccsjSFmrUZpRMeIbQ zFN6bOVMkrFa85m/7S0MDDRCAXgOH/j26Wzs0czw8T11zev0yeOd76T7TsrrxJozv9EW SEAg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=fIRfzDU/CpJ2GwUwi5qaYyALcM0b/ZoofzJjBH1j+y0=; b=IZ31usEJdvDkvDxIwTHR4ckaeIzJnE2tB8d3ybWmFscQQajIlm0B9VMDcteN4L84A7 9ZEgyN/UfdE9LnEpoc7OGadSkr9GzicAOwdVbYfyBr3B7aotCoD0V5h8VdRc6DEP/wMD a66Wn2vjHIQB8TrtBAmA9eWl1mQg04vRhFVdNJIBPRiCYW3YY4sxCpuBEo0syEYN9G8Y B1Iv00KNJKAitxxPdb+nlm6gpDvmhtL9L+aRcK1NgSie8ysbTi4Erod3BcAiSRO2+PBq CljxdRlqGuc/zS7er2xIFpZ1rwbkGhyVHTL2PkhrmaKDT8QVfQOyiDEu3UQ92pRacljX HuEA== X-Gm-Message-State: AOAM533M9nhi/7kuxpzvKVHIBuEjt2OAxdGf8iTd52qaMRBlcn9gHhge 3OlG3P3kuHrf65S5njcDyheamd8wgiUz2GoUJT4= X-Google-Smtp-Source: ABdhPJw8mhdySLWueSTV2SK7AvfuBatrn3Uj6BnJfYkemulWBsXlXDZF+yVlzCCy8onhrwG5HodIQ8JjYtYp8zFgRF8= X-Received: by 2002:ac2:510d:: with SMTP id q13mr1400930lfb.75.1619154691477; Thu, 22 Apr 2021 22:11:31 -0700 (PDT) MIME-Version: 1.0 References: <20210416202404.3443623-1-andrii@kernel.org> <20210416202404.3443623-11-andrii@kernel.org> In-Reply-To: From: Alexei Starovoitov Date: Thu, 22 Apr 2021 22:11:19 -0700 Message-ID: Subject: Re: [PATCH v2 bpf-next 10/17] libbpf: tighten BTF type ID rewriting with error checking To: Andrii Nakryiko Cc: Yonghong Song , Andrii Nakryiko , bpf , Networking , Alexei Starovoitov , Daniel Borkmann , Kernel Team Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Thu, Apr 22, 2021 at 9:25 PM Andrii Nakryiko wrote: > > On Thu, Apr 22, 2021 at 7:54 PM Alexei Starovoitov > wrote: > > > > On Thu, Apr 22, 2021 at 11:24 AM Andrii Nakryiko > > wrote: > > > > > > On Thu, Apr 22, 2021 at 9:50 AM Yonghong Song wrote: > > > > > > > > > > > > > > > > On 4/16/21 1:23 PM, Andrii Nakryiko wrote: > > > > > It should never fail, but if it does, it's better to know about this rather > > > > > than end up with nonsensical type IDs. > > > > > > > > So this is defensive programming. Maybe do another round of > > > > audit of the callers and if you didn't find any issue, you > > > > do not need to check not-happening condition here? > > > > > > It's far from obvious that this will never happen, because we do a > > > decently complicated BTF processing (we skip some types altogether > > > believing that they are not used, for example) and it will only get > > > more complicated with time. Just as there are "verifier bug" checks in > > > kernel, this prevents things from going wild if non-trivial bugs will > > > inevitably happen. > > > > I agree with Yonghong. This doesn't look right. > > I read it as Yonghong was asking about the entire patch. You seem to > be concerned with one particular check, right? > > > The callback will be called for all non-void types, right? > > so *type_id == 0 shouldn't never happen. > > If it does there is a bug somewhere that should be investigated > > instead of ignored. > > See btf_type_visit_type_ids() and btf_ext_visit_type_ids(), they call > callback for every field that contains type ID, even if it points to > VOID. So this can happen and is expected. I see. So something like 'extern cosnt void foo __ksym' would point to void type? But then why is it not a part of the id_map[] and has to be handled explicitly? > > The > > if (new_id == 0) pr_warn > > bit makes sense. > > Right, and this is the point of this patch. id_map[] will have zeroes > for any unmapped type, so I just need to make sure I'm not false > erroring on id_map[0] (== 0, which is valid, but never used). Right, id_map[0] should be 0. I'm still missing something in this combination of 'if's. May be do it as: if (new_id == 0 && *type_id != 0) { pr_warn ? That was the idea?