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

[Ricardo B. Marlière]

On Sat Mar 7, 2026 at 4:27 AM -03, Fernando Fernandez Mancera wrote:
> 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?
>> 

Nice, thank you!

>
> 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@xxxxxxxxxx>
>> ---
>
> 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.

Will do!

>
> 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;