netdev - Re: [PATCH v2] netfilter: amanda: fix RCU pointer typing for nf_nat_amanda

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Message-ID: <aYIpcHBufnxrcv5O@strlen.de>
Date: Tue, 3 Feb 2026 17:59:28 +0100
From: Florian Westphal <fw@...len.de>
To: sun jian <sun.jian.kdev@...il.com>
Cc: Pablo Neira Ayuso <pablo@...filter.org>, Phil Sutter <phil@....cc>,
	Simon Horman <horms@...nel.org>, netfilter-devel@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] netfilter: amanda: fix RCU pointer typing for
 nf_nat_amanda_hook

sun jian <sun.jian.kdev@...il.com> wrote:
> > Sun Jian <sun.jian.kdev@...il.com> wrote:
> > >  enum amanda_strings {
> > > @@ -98,7 +98,12 @@ static int amanda_help(struct sk_buff *skb,
> > >       u_int16_t len;
> > >       __be16 port;
> > >       int ret = NF_ACCEPT;
> > > -     typeof(nf_nat_amanda_hook) nf_nat_amanda;
> > > +     unsigned int (*nf_nat_amanda)(struct sk_buff *skb,
> > > +                                   enum ip_conntrack_info ctinfo,
> > > +                                   unsigned int protoff,
> > > +                                   unsigned int matchoff,
> > > +                                   unsigned int matchlen,
> > > +                                   struct nf_conntrack_expect *exp);
> >
> > Why is that needed?
> Correct. Manual declaration is indeed verbose.
> 
> The reason I used it was that typeof(nf_nat_amanda_hook) carries over
> the __rcu attribute to the local variable, which triggers a Sparse
> warning when assigning the result of rcu_dereference().

sparse doesn't generate such a warning for me.

Also, this pattern you are changing here isn't specific to amanda, it
exists elsewhere as well:

net/netfilter/nf_conntrack_snmp.c:42:23: error: incompatible types in comparison expression (different address spaces):
net/netfilter/nf_conntrack_tftp.c:78:31: error: incompatible types in comparison expression (different address spaces):
net/netfilter/nf_conntrack_irc.c:242:38: error: incompatible types in comparison expression (different address spaces):
net/netfilter/nf_conntrack_ftp.c:521:22: error: incompatible types in comparison expression (different address spaces):

so why only fix this annotation for amanda?