[PATCH 05/11 net-next v5] ipv6: prepare headers for ipv6_stub removal
From: Fernando Fernandez Mancera
Date: Wed Mar 25 2026 - 08:49:24 EST
In preparation for dropping ipv6_stub and converting its users to direct
function calls, introduce static inline dummy functions and fallback
macros in the IPv6 networking headers. In addition, introduce checks on
fib6_nh_init(), ip6_dst_lookup_flow() and ip6_fragment() to avoid a
crash due to ipv6.disable=1 set during booting. The other functions are
safe as they cannot be called with ipv6.disable=1 set.
These fallbacks ensure that when CONFIG_IPV6 is completely disabled,
there are no compiling or linking errors due to code paths not guarded
by preprocessor macro IS_ENABLED(CONFIG_IPV6).
In addition, export ndisc_send_na(), ip6_route_input() and
ip6_fragment().
Signed-off-by: Fernando Fernandez Mancera <fmancera@xxxxxxx>
Tested-by: Ricardo B. Marlière <rbm@xxxxxxxx>
---
include/net/ip6_fib.h | 32 ++++++++++++++++++++++++++++++++
include/net/ip6_route.h | 26 ++++++++++++++++++++++++++
include/net/ipv6.h | 10 ++++++++++
include/net/ndisc.h | 6 +++++-
net/ipv6/ip6_output.c | 8 ++++++++
net/ipv6/ndisc.c | 1 +
net/ipv6/route.c | 6 ++++++
7 files changed, 88 insertions(+), 1 deletion(-)
diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
index 39c98c3d8ac5..f01ef8ffe296 100644
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -486,11 +486,30 @@ void rt6_get_prefsrc(const struct rt6_info *rt, struct in6_addr *addr)
rcu_read_unlock();
}
+#if IS_ENABLED(CONFIG_IPV6)
int fib6_nh_init(struct net *net, struct fib6_nh *fib6_nh,
struct fib6_config *cfg, gfp_t gfp_flags,
struct netlink_ext_ack *extack);
void fib6_nh_release(struct fib6_nh *fib6_nh);
void fib6_nh_release_dsts(struct fib6_nh *fib6_nh);
+#else
+static inline int fib6_nh_init(struct net *net, struct fib6_nh *fib6_nh,
+ struct fib6_config *cfg, gfp_t gfp_flags,
+ struct netlink_ext_ack *extack)
+{
+ NL_SET_ERR_MSG(extack, "IPv6 support not enabled in kernel");
+ return -EAFNOSUPPORT;
+}
+
+static inline void fib6_nh_release(struct fib6_nh *fib6_nh)
+{
+}
+
+static inline void fib6_nh_release_dsts(struct fib6_nh *fib6_nh)
+{
+}
+#endif
+
int call_fib6_entry_notifiers(struct net *net,
enum fib_event_type event_type,
@@ -502,8 +521,15 @@ int call_fib6_multipath_entry_notifiers(struct net *net,
unsigned int nsiblings,
struct netlink_ext_ack *extack);
int call_fib6_entry_notifiers_replace(struct net *net, struct fib6_info *rt);
+#if IS_ENABLED(CONFIG_IPV6)
void fib6_rt_update(struct net *net, struct fib6_info *rt,
struct nl_info *info);
+#else
+static inline void fib6_rt_update(struct net *net, struct fib6_info *rt,
+ struct nl_info *info)
+{
+}
+#endif
void inet6_rt_notify(int event, struct fib6_info *rt, struct nl_info *info,
unsigned int flags);
@@ -569,7 +595,13 @@ int fib6_tables_dump(struct net *net, struct notifier_block *nb,
struct netlink_ext_ack *extack);
void fib6_update_sernum(struct net *net, struct fib6_info *rt);
+#if IS_ENABLED(CONFIG_IPV6)
void fib6_update_sernum_upto_root(struct net *net, struct fib6_info *rt);
+#else
+static inline void fib6_update_sernum_upto_root(struct net *net, struct fib6_info *rt)
+{
+}
+#endif
void fib6_update_sernum_stub(struct net *net, struct fib6_info *f6i);
void fib6_metric_set(struct fib6_info *f6i, int metric, u32 val);
diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index 0c8eeb6abe7a..09ffe0f13ce7 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -77,7 +77,14 @@ static inline bool rt6_qualify_for_ecmp(const struct fib6_info *f6i)
f6i->fib6_nh->fib_nh_gw_family;
}
+#if IS_ENABLED(CONFIG_IPV6)
void ip6_route_input(struct sk_buff *skb);
+#else
+static inline void ip6_route_input(struct sk_buff *skb)
+{
+}
+#endif
+
struct dst_entry *ip6_route_input_lookup(struct net *net,
struct net_device *dev,
struct flowi6 *fl6,
@@ -119,7 +126,15 @@ int ipv6_route_ioctl(struct net *net, unsigned int cmd,
int ip6_route_add(struct fib6_config *cfg, gfp_t gfp_flags,
struct netlink_ext_ack *extack);
int ip6_ins_rt(struct net *net, struct fib6_info *f6i);
+#if IS_ENABLED(CONFIG_IPV6)
int ip6_del_rt(struct net *net, struct fib6_info *f6i, bool skip_notify);
+#else
+static inline int ip6_del_rt(struct net *net, struct fib6_info *f6i,
+ bool skip_notify)
+{
+ return -EAFNOSUPPORT;
+}
+#endif
void rt6_flush_exceptions(struct fib6_info *f6i);
void rt6_age_exceptions(struct fib6_info *f6i, struct fib6_gc_args *gc_args,
@@ -270,8 +285,19 @@ static inline bool ipv6_anycast_destination(const struct dst_entry *dst,
return __ipv6_anycast_destination(&rt->rt6i_dst, rt->rt6i_flags, daddr);
}
+#if IS_ENABLED(CONFIG_IPV6)
int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
int (*output)(struct net *, struct sock *, struct sk_buff *));
+#else
+static inline int ip6_fragment(struct net *net, struct sock *sk,
+ struct sk_buff *skb,
+ int (*output)(struct net *, struct sock *,
+ struct sk_buff *))
+{
+ kfree_skb(skb);
+ return -EAFNOSUPPORT;
+}
+#endif
/* Variant of dst_mtu() for IPv6 users */
static inline u32 dst6_mtu(const struct dst_entry *dst)
diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index 0958cc5c6ec3..f99f273341f0 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -1044,8 +1044,18 @@ static inline struct sk_buff *ip6_finish_skb(struct sock *sk)
int ip6_dst_lookup(struct net *net, struct sock *sk, struct dst_entry **dst,
struct flowi6 *fl6);
+#if IS_ENABLED(CONFIG_IPV6)
struct dst_entry *ip6_dst_lookup_flow(struct net *net, const struct sock *sk, struct flowi6 *fl6,
const struct in6_addr *final_dst);
+#else
+static inline struct dst_entry *ip6_dst_lookup_flow(struct net *net, const struct sock *sk,
+ struct flowi6 *fl6,
+ const struct in6_addr *final_dst)
+{
+ return ERR_PTR(-EAFNOSUPPORT);
+}
+#endif
+
struct dst_entry *ip6_sk_dst_lookup_flow(struct sock *sk, struct flowi6 *fl6,
const struct in6_addr *final_dst,
bool connected);
diff --git a/include/net/ndisc.h b/include/net/ndisc.h
index d38783a2ce57..19e2a177bd29 100644
--- a/include/net/ndisc.h
+++ b/include/net/ndisc.h
@@ -406,13 +406,17 @@ static inline void __ipv6_confirm_neigh_stub(struct net_device *dev,
static inline struct neighbour *ip_neigh_gw6(struct net_device *dev,
const void *addr)
{
+#if IS_ENABLED(CONFIG_IPV6)
struct neighbour *neigh;
neigh = __ipv6_neigh_lookup_noref_stub(dev, addr);
if (unlikely(!neigh))
- neigh = __neigh_create(ipv6_stub->nd_tbl, addr, dev, false);
+ neigh = __neigh_create(&nd_tbl, addr, dev, false);
return neigh;
+#else
+ return ERR_PTR(-EAFNOSUPPORT);
+#endif
}
int ndisc_init(void);
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 8e2a6b28cea7..63abc4fddaee 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -873,6 +873,11 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
__be32 frag_id;
u8 *prevhdr, nexthdr = 0;
+ if (!ipv6_mod_enabled()) {
+ kfree_skb(skb);
+ return -EAFNOSUPPORT;
+ }
+
err = ip6_find_1stfragopt(skb, &prevhdr);
if (err < 0)
goto fail;
@@ -1045,6 +1050,7 @@ int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
kfree_skb(skb);
return err;
}
+EXPORT_SYMBOL_GPL(ip6_fragment);
static inline int ip6_rt_check(const struct rt6key *rt_key,
const struct in6_addr *fl_addr,
@@ -1256,6 +1262,8 @@ struct dst_entry *ip6_dst_lookup_flow(struct net *net, const struct sock *sk, st
struct dst_entry *dst = NULL;
int err;
+ if (!ipv6_mod_enabled())
+ return ERR_PTR(-EAFNOSUPPORT);
err = ip6_dst_lookup_tail(net, sk, &dst, fl6);
if (err)
return ERR_PTR(err);
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index f6a5d8c73af9..f76fb8a85452 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -576,6 +576,7 @@ void ndisc_send_na(struct net_device *dev, const struct in6_addr *daddr,
ndisc_send_skb(skb, daddr, src_addr);
}
+EXPORT_SYMBOL_GPL(ndisc_send_na);
static void ndisc_send_unsol_na(struct net_device *dev)
{
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 781b43c54932..844a70ea3567 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2655,6 +2655,7 @@ void ip6_route_input(struct sk_buff *skb)
skb_dst_set_noref(skb, ip6_route_input_lookup(net, skb->dev,
&fl6, skb, flags));
}
+EXPORT_SYMBOL_GPL(ip6_route_input);
INDIRECT_CALLABLE_SCOPE struct rt6_info *ip6_pol_route_output(struct net *net,
struct fib6_table *table,
@@ -3585,6 +3586,11 @@ int fib6_nh_init(struct net *net, struct fib6_nh *fib6_nh,
struct inet6_dev *idev = NULL;
int err;
+ if (!ipv6_mod_enabled()) {
+ NL_SET_ERR_MSG(extack, "IPv6 support not enabled in kernel");
+ return -EAFNOSUPPORT;
+ }
+
fib6_nh->fib_nh_family = AF_INET6;
#ifdef CONFIG_IPV6_ROUTER_PREF
fib6_nh->last_probe = jiffies;
--
2.53.0