Re: [PATCH wireguard] wireguard: prevent ipv6 addrconf via IFF_NO_ADDRCONF flag

Re: [PATCH wireguard] wireguard: prevent ipv6 addrconf via IFF_NO_ADDRCONF flag

[Jason A. Donenfeld]

Hi Valentin,

On Sun, Feb 08, 2026 at 06:05:45PM +0100, Valentin Spreckels wrote:
> Use the flag introduced in commit 8a321cf7becc6 ("net: add
> IFF_NO_ADDRCONF and use it in bonding to prevent ipv6 addrconf")
> instead of mangling the addr_gen_mode to prevent ipv6 addrconf.

Can you give some more context here? Why was IFF_NO_ADDRCONF added when
the IN6_ADDR_GEN_MODE_NONE method has been working fine? What's the
difference between these approaches? I don't doubt that your patch is
correct, but I would like to better understand this.

Jason

Re: [PATCH wireguard] wireguard: prevent ipv6 addrconf via IFF_NO_ADDRCONF flag

[Valentin Spreckels]

Hi Jason,

On 11/03/2026 23:59, Jason A. Donenfeld wrote:
> Hi Valentin,
> 
> On Sun, Feb 08, 2026 at 06:05:45PM +0100, Valentin Spreckels wrote:
>> Use the flag introduced in commit 8a321cf7becc6 ("net: add
>> IFF_NO_ADDRCONF and use it in bonding to prevent ipv6 addrconf")
>> instead of mangling the addr_gen_mode to prevent ipv6 addrconf.
> 
> Can you give some more context here? Why was IFF_NO_ADDRCONF added when
> the IN6_ADDR_GEN_MODE_NONE method has been working fine? What's the
> difference between these approaches? I don't doubt that your patch is
> correct, but I would like to better understand this.

Only wireguard configures addr_gen_mode inside the kernel, otherwise it 
is only set by userspace; userspace is also able to overwrite the 
IFF_NO_ADDRCONF set by wireguard.

Commit 8a321cf7becc ("net: add IFF_NO_ADDRCONF and use it in bonding to 
prevent ipv6 addrconf") introduces the private interface flag 
IFF_NO_ADDRCONF, which isn't accessible by userspace.

Thus use the IFF_NO_ADDRCONF flag in wireguard.


Does that answer your questions? If yes, I will submit a v2 with this as 
commit message.

Best regards

Valentin