Re: [PATCH] netfilter: nf_conntrack_sip: fix the ct_sip_parse_numerical_param() return value.

[Simon Horman]

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@xxxxxxxxxxx>
> > 
> > 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