Re: [PATCH bpf-next v2] bpf, unix: Guard sk_msg-dependent code behind CONFIG_NET_SOCK_MSG

[Jakub Sitnicki <jakub@cloudflare.com>]

On Tue, Jun 23, 2026 at 09:08 AM -07, Kuniyuki Iwashima wrote:
> On Tue, Jun 23, 2026 at 4:20 AM Jakub Sitnicki <jakub@cloudflare.com> wrote:
>>
>> Prepare to decouple BPF_SYSCALL config option from NET_SOCK_MSG. When
>> completed all code paths related to sockmap-based redirects should be
>> guarded by BPF_SYSCALL && NET_SOCK_MSG to allow users to opt out by
>> disabling NET_SOCK_MSG. The implementation of sockmap as a container for
>> socket references would remain under BPF_SYSCALL.
>>
>> Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
>> ---
>> Changes in v2:
>> - Handle prot->recvmsg being NULL (Sashiko)
>> - Elaborate on the end goal in description
>> - Link to v1: https://patch.msgid.link/20260622-bpf-sk_msg-split-unix-v1-1-d7e0cb7bb03b@cloudflare.com
>> ---
>>  net/unix/af_unix.c  | 4 ++--
>>  net/unix/unix_bpf.c | 6 ++++++
>>  2 files changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
>> index f7a9d55eee8a..84c11c60c75f 100644
>> --- a/net/unix/af_unix.c
>> +++ b/net/unix/af_unix.c
>> @@ -2675,7 +2675,7 @@ static int unix_dgram_recvmsg(struct socket *sock, struct msghdr *msg, size_t si
>>  #ifdef CONFIG_BPF_SYSCALL
>>         const struct proto *prot = READ_ONCE(sk->sk_prot);
>>
>> -       if (prot != &unix_dgram_proto)
>> +       if (prot->recvmsg)
>
> There is no reason to have this dead branch when
> CONFIG_BPF_SYSCALL && !NET_SOCK_MSG.
>
> Let's compile out all sockmap code when both configs
> are not enabled.
>
> Since AF_UNIX differs from TCP/UDP, it can take the
> simpler approach.

Okay, will put the whole file behind hidden config option like so:

--- a/net/unix/Kconfig
+++ b/net/unix/Kconfig
@@ -30,3 +30,8 @@ config UNIX_DIAG
        help
          Support for UNIX socket monitoring interface used by the ss tool.
          If unsure, say Y.
+
+config UNIX_BPF
+       bool
+       depends on UNIX
+       default y if BPF_SYSCALL && NET_SOCK_MSG