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=-6.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 90F31C43215 for ; Thu, 14 Nov 2019 00:31:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9AB97206D8 for ; Thu, 14 Nov 2019 00:31:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="Hlj6rDrl" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727237AbfKNAbo (ORCPT ); Wed, 13 Nov 2019 19:31:44 -0500 Received: from mail-pg1-f195.google.com ([209.85.215.195]:40716 "EHLO mail-pg1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726910AbfKNAbn (ORCPT ); Wed, 13 Nov 2019 19:31:43 -0500 Received: by mail-pg1-f195.google.com with SMTP id 15so2473335pgt.7 for ; Wed, 13 Nov 2019 16:31:42 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=9sAWI1/WyVUJMv+/9lzXmr/UTEtbsKqgfoRGVLEnFt8=; b=Hlj6rDrliTvU/cepY3VqIv8iG73LNRL7563tZytDrLShqFopNYrRCLMIQdo9EA6jDE FInBRd96HhgghlpO3VGkTnv17MaY+PkaVo6Vpr8glXkHGY3k+2KW690kk3LBlh3tLN/K QHzIckFi5j/6rdruMb2CNBcJ8fpyccBBCzhrw= 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; bh=9sAWI1/WyVUJMv+/9lzXmr/UTEtbsKqgfoRGVLEnFt8=; b=F6ezoEC+q7MlAqpGnE+UFMTwiBRDRZJTk3uPxCghyskI32QfL0Cy1kQI/hWb4i5vl2 AtTpJQ1ExAILM/TuCnshaM54Av/d0VdF/Od6JoBfbGyO6LnJJPjPkXgRmKjZaatsmrpp dpR/BDzwb3mdI77KEpausrTEsKWJGITmY0XqYfuNkV+zMCkraza2h1lpKezc4yH/dlbz 9iDTc1hue0e2MXd8PQUxsbNFrgNGJB2IX73DzTKN6FCZZYgbzbNIdhQADjRWPOOlGepb 1lgONhbd9f37twonuZvHtVIfZ5ih16FE+9E7YkRiEhRZMKDCl4D1+68LWZL3L9iDZlf/ Ca8Q== X-Gm-Message-State: APjAAAVsBTYU5Oa8ZNZIIAhs8uO64Hil/SI9ns0zfCEZzVOwnEeaZ+0h H0g1CWPj11l03SYPJWJHgnoa1K9UGo4= X-Google-Smtp-Source: APXvYqy73l8AcMr+AtoYg+/uiIszTaLYGFq4eHui1Ai1uiPyzjRywtbILY5sc/7uW/xNvwGKPlOrWQ== X-Received: by 2002:a17:90a:a898:: with SMTP id h24mr8777377pjq.48.1573691502087; Wed, 13 Nov 2019 16:31:42 -0800 (PST) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id d22sm3672614pjd.2.2019.11.13.16.31.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Nov 2019 16:31:41 -0800 (PST) Date: Wed, 13 Nov 2019 16:31:40 -0800 From: Kees Cook To: "Jason A. Donenfeld" Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] net: print proper warning on dst underflow Message-ID: <201911131625.8B0F0BAEDE@keescook> References: <20190924090937.13001-1-Jason@zx2c4.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190924090937.13001-1-Jason@zx2c4.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 24, 2019 at 11:09:37AM +0200, Jason A. Donenfeld wrote: > Proper warnings with stack traces make it much easier to figure out > what's doing the double free and create more meaningful bug reports from > users. > > Signed-off-by: Jason A. Donenfeld > --- > net/core/dst.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/net/core/dst.c b/net/core/dst.c > index 1325316d9eab..193af526e908 100644 > --- a/net/core/dst.c > +++ b/net/core/dst.c > @@ -172,7 +172,7 @@ void dst_release(struct dst_entry *dst) > int newrefcnt; > > newrefcnt = atomic_dec_return(&dst->__refcnt); > - if (unlikely(newrefcnt < 0)) > + if (WARN_ONCE(newrefcnt < 0, "dst_release underflow")) > net_warn_ratelimited("%s: dst:%p refcnt:%d\n", > __func__, dst, newrefcnt); Should __refcnt be a refcount_t to gain saturation protection? It seems like going negative is bad... -Kees > if (!newrefcnt) > @@ -187,7 +187,7 @@ void dst_release_immediate(struct dst_entry *dst) > int newrefcnt; > > newrefcnt = atomic_dec_return(&dst->__refcnt); > - if (unlikely(newrefcnt < 0)) > + if (WARN_ONCE(newrefcnt < 0, "dst_release_immediate underflow")) > net_warn_ratelimited("%s: dst:%p refcnt:%d\n", > __func__, dst, newrefcnt); > if (!newrefcnt) > -- > 2.21.0 > -- Kees Cook