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Message-ID: <ZFEuazEvNWHfEH93@corigine.com> Date: Tue, 2 May 2023 17:38:19 +0200 From: Simon Horman <simon.horman@...igine.com> To: Gavrilov Ilia <Ilia.Gavrilov@...otecs.ru> Cc: Pablo Neira Ayuso <pablo@...filter.org>, Jozsef Kadlecsik <kadlec@...filter.org>, Florian Westphal <fw@...len.de>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Patrick McHardy <kaber@...sh.net>, "netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>, "coreteam@...filter.org" <coreteam@...filter.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "lvc-project@...uxtesting.org" <lvc-project@...uxtesting.org> Subject: Re: [PATCH] netfilter: nf_conntrack_sip: fix the ct_sip_parse_numerical_param() return value. On Tue, May 02, 2023 at 02:16:09PM +0000, Gavrilov Ilia wrote: > On 5/2/23 17:05, Simon Horman wrote: > > On Tue, May 02, 2023 at 11:43:19AM +0000, Gavrilov Ilia wrote: > >> On 4/28/23 22:24, Simon Horman wrote: > >>> On Wed, Apr 26, 2023 at 03:04:31PM +0000, Gavrilov Ilia wrote: > >>>> ct_sip_parse_numerical_param() returns only 0 or 1 now. > >>>> But process_register_request() and process_register_response() imply > >>>> checking for a negative value if parsing of a numerical header parameter > >>>> failed. Let's fix it. > >>>> > >>>> Found by InfoTeCS on behalf of Linux Verification Center > >>>> (linuxtesting.org) with SVACE. > >>>> > >>>> Fixes: 0f32a40fc91a ("[NETFILTER]: nf_conntrack_sip: create signalling expectations") > >>>> Signed-off-by: Ilia.Gavrilov <Ilia.Gavrilov@...otecs.ru> > >>> > >>> Hi Gavrilov, > >>> > >> > >> Hi Simon, thank you for your answer. > >> > >>> although it is a slightly unusual convention for kernel code, > >>> I believe the intention is that this function returns 0 when > >>> it fails (to parse) and 1 on success. So I think that part is fine. > >>> > >>> What seems a bit broken is the way that callers use the return value. > >>> > >>> 1. The call in process_register_response() looks like this: > >>> > >>> ret = ct_sip_parse_numerical_param(...) > >>> if (ret < 0) { > >>> nf_ct_helper_log(skb, ct, "cannot parse expires"); > >>> return NF_DROP; > >>> } > >>> > >>> But ret can only be 0 or 1, so the error handling is never inoked, > >>> and a failure to parse is ignored. I guess failure doesn't occur in > >>> practice. > >>> > >>> I suspect this should be: > >>> > >>> ret = ct_sip_parse_numerical_param(...) > >>> if (!ret) { > >>> nf_ct_helper_log(skb, ct, "cannot parse expires"); > >>> return NF_DROP; > >>> } > >>> > >> > >> ct_sip_parse_numerical_param() returns 0 in to cases 1) when the > >> parameter 'expires=' isn't found in the header or 2) it's incorrectly set. > >> In the first case, the return value should be ignored, since this is a > >> normal situation > >> In the second case, it's better to write to the log and return NF_DROP, > >> or ignore it too, then checking the return value can be removed as > >> unnecessary. > > > > Sorry, I think I misunderstood the intention of your patch earlier. > > > > Do I (now) understand correctly that you are proposing a tristate? > > > > a) return 1 if value is found; *val is set > > b) return 0 if value is not found; *val is unchanged > > c) return -1 on error; *val is undefined > > Yes, it seems to me that this was originally intended. Thanks. With my new found understanding, this looks good to me. Reviewed-by: Simon Horman <simon.horman@...igine.com>
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