Re: [RESEND PATCH net v5 1/2] tun: keep a kernel copy of the socket filter program

[Jakub Kicinski <kuba@kernel.org>]

On Mon, 12 Oct 2026 10:11:12 +0800 Rongguang Wei wrote:
> +/**
> + * sk_attach_filter_kern - attach a classic BPF filter held in kernel memory
> + * @fprog: program to attach, with @fprog->filter pointing at kernel memory
> + * @sk: socket to attach the filter to
> + *
> + * Attach a copy of a classic BPF program that the kernel already holds, the
> + * way sk_attach_filter() does for one that still lives in user space. The
> + * caller must hold the socket lock; SOCK_FILTER_LOCKED is checked here.
> + *
> + * The program is built by bpf_prog_create(), which does not keep an original
> + * copy of the instructions. sk_get_filter() therefore returns -EACCES and
> + * sock_diag leaves the filter out for a socket that uses this helper. A
> + * classic BPF program cannot be duplicated with bpf_prog_copy(), so keeping
> + * the original would cost another allocation and a copy per attach.
> + */
> +int sk_attach_filter_kern(struct sock_fprog_kern *fprog, struct sock *sk)

Warning: net/core/filter.c:1585 No description found for return value of 'sk_attach_filter_kern'
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