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[198.0.35.241]) by smtp.gmail.com with ESMTPSA id mt15-20020a17090b230f00b00212d9a06edcsm870576pjb.42.2022.11.17.16.25.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 17 Nov 2022 16:25:30 -0800 (PST) Date: Thu, 17 Nov 2022 16:25:29 -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: <202211171624.963F44FCE@keescook> References: <202211171422.7A7A7A9@keescook> <202211171513.28D070E@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: netdev@vger.kernel.org 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 :) -- Kees Cook