Subject: Re: [PATCH net-next v2 1/3] netfilter: conntrack: add shared port parser for helpers

From: Phil Sutter <[email-masked]>
Date: Fri, 1 May 2026 12:25:01 +0200

Hi,

On Fri, May 01, 2026 at 12:01:54PM +0530, HACKE-RC wrote:
> Add nf_ct_helper_parse_port() to the conntrack helper core. This
> provides a port parser that does not rely on nul-terminated strings,
> taking an explicit length parameter and validating the result fits
> in the 1-65535 range.
> 
> Modeled after the approach in 8cf6809cddcb ("netfilter:
> nf_conntrack_sip: don't use simple_strtoul") but as a shared
> function so IRC, Amanda, and other helpers can use it instead of
> open-coding simple_strtoul calls with ad-hoc range checks.
> 
> Signed-off-by: HACKE-RC <[email-masked]>
> ---
>  include/net/netfilter/nf_conntrack_helper.h |  3 +++
>  net/netfilter/nf_conntrack_helper.c         | 28 +++++++++++++++++++++
>  2 files changed, 31 insertions(+)
> 
> diff --git a/include/net/netfilter/nf_conntrack_helper.h b/include/net/netfilter/nf_conntrack_helper.h
> index de2f956ab..db19fe25f 100644
> --- a/include/net/netfilter/nf_conntrack_helper.h
> +++ b/include/net/netfilter/nf_conntrack_helper.h
> @@ -160,6 +160,9 @@ nf_ct_helper_expectfn_find_by_name(const char *name);
>  struct nf_ct_helper_expectfn *
>  nf_ct_helper_expectfn_find_by_symbol(const void *symbol);
>  
> +int nf_ct_helper_parse_port(const char *cp, unsigned int len,
> +			    u16 *port, char **endp);
> +
>  extern struct hlist_head *nf_ct_helper_hash;
>  extern unsigned int nf_ct_helper_hsize;
>  
> diff --git a/net/netfilter/nf_conntrack_helper.c b/net/netfilter/nf_conntrack_helper.c
> index a715304a5..12f51670d 100644
> --- a/net/netfilter/nf_conntrack_helper.c
> +++ b/net/netfilter/nf_conntrack_helper.c
> @@ -499,6 +499,34 @@ void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat)
>  }
>  EXPORT_SYMBOL_GPL(nf_nat_helper_unregister);
>  
> +int nf_ct_helper_parse_port(const char *cp, unsigned int len,
> +			    u16 *port, char **endp)
> +{
> +	unsigned long result = 0;
> +	const char *start = cp;
> +
> +	while (len > 0 && *cp >= '0' && *cp <= '9') {
> +		result = result * 10 + (*cp - '0');
> +		if (result > 65535)
> +			return -1;
> +		cp++;
> +		len--;
> +	}
> +
> +	if (cp == start)
> +		return -1;

This check is redundant wrt. the following one: If the loop didn't
increment 'cp', result must be zero. So you may just drop it entirely.

Cheers, Phil

> +
> +	if (result == 0)
> +		return -1;
> +
> +	*port = result;
> +	if (endp)
> +		*endp = (char *)cp;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(nf_ct_helper_parse_port);
> +
>  int nf_conntrack_helper_init(void)
>  {
>  	nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
> -- 
> 2.54.0
> 
>