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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9FA3DC4332F for ; Fri, 18 Nov 2022 02:16:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240970AbiKRCQT (ORCPT ); Thu, 17 Nov 2022 21:16:19 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43452 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240848AbiKRCQQ (ORCPT ); Thu, 17 Nov 2022 21:16:16 -0500 Received: from mail-pl1-x636.google.com (mail-pl1-x636.google.com [IPv6:2607:f8b0:4864:20::636]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0370062070 for ; Thu, 17 Nov 2022 18:16:15 -0800 (PST) Received: by mail-pl1-x636.google.com with SMTP id p12so3347650plq.4 for ; Thu, 17 Nov 2022 18:16:14 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=+SkZRkkef+v6G+0a9+2iS5p4d3ejFxRmaBjvvBIsMgg=; b=eEoKCv3TZAm+ottsO1B4CP5IM82E8KOLN6QySwO8bqXZqYslWxeaMnokpMhMqBjF3u NwEsQ3qwp166kcRrwJcusmJ1zwWRhnJAuBmDlvQBjtO+AnM4ZkuZaa9Imjghi/qj/WM4 tzD3a9eP674896nEw3EBljo2xY0mGNohU3GUk= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=+SkZRkkef+v6G+0a9+2iS5p4d3ejFxRmaBjvvBIsMgg=; b=YDP8k6x7uIoXruigOrFMRl1Qq4PsStpKCR+UJ5iITD0oSE4MEQ9EQmgAatN38O5Fgw ++APfWqo2+o6Ey69GO3ApwHVgq/gmB1n2OXiGF4fCNwYH5EpvOHpmk+rah50BWRfQ+kU 6bMZM4COaMb52QLzVikdb1DwhOgiYAUGGJbylmEPUho1/nErEUyaKUo9jl4SK8i6D3fD w0r+s/evVVpiIGR7mJIQLqDE91oV94kOwFmkMr6C0iLGp5xOmNNw00nFoe/VbzQnhKRH MwsqRhyg7+IQKYyPTWy813XTv7ClBiDyCLJmEqAbum3drozAYHFr217raTtQDIsSo5UT YEQw== X-Gm-Message-State: ANoB5pmPq82YAXe2Fm5sFm4qmheOGl6np5OVScTmfH5MWNT9wCO8+tU5 s9DZ2OMsFWzWDdmdtxPDKlNUew== X-Google-Smtp-Source: AA0mqf4hAKoAqczugH/ufOKcBGcmCRT4026qHVeOERU/ya6eaV8vq/bdEj/zV8RJtOP/t4+9HlVXEg== X-Received: by 2002:a17:902:8645:b0:188:d6e1:b82b with SMTP id y5-20020a170902864500b00188d6e1b82bmr5400452plt.146.1668737774485; Thu, 17 Nov 2022 18:16:14 -0800 (PST) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id q17-20020a170902dad100b001886863c6absm2175114plx.97.2022.11.17.18.16.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 17 Nov 2022 18:16:13 -0800 (PST) Date: Thu, 17 Nov 2022 18:16:12 -0800 From: Kees Cook To: Eric Dumazet Cc: linux-kernel@vger.kernel.org, Marc Kleine-Budde , Paolo Abeni , Stefano Garzarella , Jakub Kicinski , Nikolay Aleksandrov , "David S. Miller" , Florian Fainelli , netdev@vger.kernel.org, "Gustavo A. R. Silva" , linux-next@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: Coverity: __sock_gen_cookie(): Error handling issues Message-ID: <202211171815.D076ED9C@keescook> References: <202211171422.7A7A7A9@keescook> <202211171513.28D070E@keescook> <202211171624.963F44FCE@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 17, 2022 at 05:24:36PM -0800, Eric Dumazet wrote: > On Thu, Nov 17, 2022 at 4:25 PM Kees Cook wrote: > > > > On Thu, Nov 17, 2022 at 03:22:22PM -0800, Eric Dumazet wrote: > > > On Thu, Nov 17, 2022 at 3:14 PM Kees Cook wrote: > > > > > > > > On Thu, Nov 17, 2022 at 02:49:55PM -0800, Eric Dumazet wrote: > > > > > On Thu, Nov 17, 2022 at 2:22 PM coverity-bot wrote: > > > > > > > > > > > > Hello! > > > > > > > > > > > > This is an experimental semi-automated report about issues detected by > > > > > > Coverity from a scan of next-20221117 as part of the linux-next scan project: > > > > > > https://scan.coverity.com/projects/linux-next-weekly-scan > > > > > > > > > > > > You're getting this email because you were associated with the identified > > > > > > lines of code (noted below) that were touched by commits: > > > > > > > > > > > > Wed Nov 16 12:42:01 2022 +0000 > > > > > > 4ebf802cf1c6 ("net: __sock_gen_cookie() cleanup") > > > > > > > > > > > > Coverity reported the following: > > > > > > > > > > > > *** CID 1527347: Error handling issues (CHECKED_RETURN) > > > > > > net/core/sock_diag.c:33 in __sock_gen_cookie() > > > > > > 27 { > > > > > > 28 u64 res = atomic64_read(&sk->sk_cookie); > > > > > > 29 > > > > > > 30 if (!res) { > > > > > > 31 u64 new = gen_cookie_next(&sock_cookie); > > > > > > 32 > > > > > > vvv CID 1527347: Error handling issues (CHECKED_RETURN) > > > > > > vvv Calling "atomic64_try_cmpxchg" without checking return value (as is done elsewhere 8 out of 9 times). > > > > > > 33 atomic64_try_cmpxchg(&sk->sk_cookie, &res, new); > > > > > > > > > > > > > > > Hmmm. for some reason I thought @res was always updated... > > > > > > > > > > A fix would be to read sk->sk_cookie, but I guess your tool will still > > > > > complain we do not care > > > > > of atomic64_try_cmpxchg() return value ? > > > > > > > > > > diff --git a/net/core/sock_diag.c b/net/core/sock_diag.c > > > > > index b11593cae5a09b15a10d6ba35bccc22263cb8fc8..58efb9c1c8dd4f8e5a3009a0176e1b96487daaff > > > > > 100644 > > > > > --- a/net/core/sock_diag.c > > > > > +++ b/net/core/sock_diag.c > > > > > @@ -31,6 +31,10 @@ u64 __sock_gen_cookie(struct sock *sk) > > > > > u64 new = gen_cookie_next(&sock_cookie); > > > > > > > > > > atomic64_try_cmpxchg(&sk->sk_cookie, &res, new); > > > > > + /* Another cpu/thread might have won the race, > > > > > + * reload the final value. > > > > > + */ > > > > > + res = atomic64_read(&sk->sk_cookie); > > > > > } > > > > > return res; > > > > > } > > > > > > > > I think it's saying it was expecting an update loop -- i.e. to make sure > > > > the value actually got swapped (the "try" part...)? > > > > > > The value has been updated, either by us or someone else. > > > > > > We do not particularly care who won the race, since the value is > > > updated once only. > > > > Ah! Okay, now I understand the added comment. Thanks :) > > I guess we could simply go back to atomic64_cmpxchg() to avoid a false positive. It looks like the existing code already works as intended, so no need to silence the warning. The comment and reload might be nice to add, just to clarify for anyone looking at it again in the future, though. -- Kees Cook