Re: [PATCH net v3 2/3] bpf: bpf_out_neigh_v6: Fix nd_tbl NULL dereference when IPv6 is disabled

[Fernando Fernandez Mancera <fmancera@suse.de>]

On 3/7/26 3:39 AM, Jakub Kicinski wrote:
> On Fri, 6 Mar 2026 10:58:44 +0100 Fernando Fernandez Mancera wrote:
>>>> +	if (unlikely(!ipv6_stub->nd_tbl))
>>>> +		goto out_drop;
>>>
>>> So neither Fernando nor you checked whether this code can be built
>>> as a module? ipv6_mod_enabled() should work just fine
>>
>> I checked it. If IPV6=m this is not fine.
>>
>> ld: vmlinux.o: in function `bpf_out_neigh_v6':
>> filter.c:(.text+0x3231d60): undefined reference to `ipv6_mod_enabled'
> 
> Guess I got it backwards :/ Should we add this to the series?
> 

No worries.

> -->8--------
> Subject: ipv6: move the disable_ipv6_mod knob to core code
> 
> Make sure disable_ipv6_mod itself is not part of the IPv6 module,
> in case core code wants to refer to it. We will remove support
> for IPv6=m soon, this change helps make fixes we commit before
> that less messy.
> 
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> ---

Ricardo could you add it and check if it is fine? FWIW; I am sending 
today the series removing IPV6=m after some testing to net-next tree.

Thanks,
Fernando.

>   include/linux/ipv6.h | 7 ++++++-
>   net/ipv4/af_inet.c   | 6 ++++++
>   net/ipv6/af_inet6.c  | 8 --------
>   3 files changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
> index 443053a76dcf..e5b6853d517a 100644
> --- a/include/linux/ipv6.h
> +++ b/include/linux/ipv6.h
> @@ -333,7 +333,12 @@ struct tcp6_timewait_sock {
>   };
>   
>   #if IS_ENABLED(CONFIG_IPV6)
> -bool ipv6_mod_enabled(void);
> +extern int disable_ipv6_mod;
> +
> +static inline bool ipv6_mod_enabled(void)
> +{
> +        return disable_ipv6_mod == 0;
> +}
>   
>   static inline struct ipv6_pinfo *inet6_sk(const struct sock *__sk)
>   {
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index babcd75a08e2..f1944e8fd9d3 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -124,6 +124,12 @@
>   
>   #include <trace/events/sock.h>
>   
> +/* Keep the definition of IPv6 disable here for now, to avoid annoying linker
> + * issues in case IPv6=m
> + */
> +int disable_ipv6_mod;
> +EXPORT_SYMBOL(disable_ipv6_mod);
> +
>   /* The inetsw table contains everything that inet_create needs to
>    * build a new socket.
>    */
> diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
> index 0b995a961359..03c175cbbdb6 100644
> --- a/net/ipv6/af_inet6.c
> +++ b/net/ipv6/af_inet6.c
> @@ -86,8 +86,6 @@ struct ipv6_params ipv6_defaults = {
>   	.autoconf = 1,
>   };
>   
> -static int disable_ipv6_mod;
> -
>   module_param_named(disable, disable_ipv6_mod, int, 0444);
>   MODULE_PARM_DESC(disable, "Disable IPv6 module such that it is non-functional");
>   
> @@ -97,12 +95,6 @@ MODULE_PARM_DESC(disable_ipv6, "Disable IPv6 on all interfaces");
>   module_param_named(autoconf, ipv6_defaults.autoconf, int, 0444);
>   MODULE_PARM_DESC(autoconf, "Enable IPv6 address autoconfiguration on all interfaces");
>   
> -bool ipv6_mod_enabled(void)
> -{
> -	return disable_ipv6_mod == 0;
> -}
> -EXPORT_SYMBOL_GPL(ipv6_mod_enabled);
> -
>   static struct ipv6_pinfo *inet6_sk_generic(struct sock *sk)
>   {
>   	const int offset = sk->sk_prot->ipv6_pinfo_offset;