Re: [PATCH bpf v2 06/15] bpf, sockmap: Give no progs to a TCP listener

[John Fastabend <john.fastabend@gmail.com>]

On Mon, 02 Nov 2026 00:21, Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
>From: Chris Mason <mason@kernel.org>
>
>A psock with a verdict prog replaces sk_data_ready and sk_write_space of
>its socket. It saves the old callbacks, and the new callbacks call them.
>sock_map_link() does this to a TCP listener too. Its new sk_data_ready
>cannot read and does not call the old one. Thus it does not wake accept().
>
>sk_clone() copies the new callbacks to each child, but not the psock.
>tcp_bpf_clone() restores only sk_prot. Without a psock the child loses data
>or does not wake its reader. If it gets a psock, the psock saves the copies
>as the old callbacks. Then sk_psock_verdict_data_ready() calls itself until
>the stack overflows. sk_psock_write_space() calls itself too, without end.
>
>Give no progs to a TCP listener, as before the first commit below. A
>listener receives and sends no data. It stays in the map and keeps its own
>callbacks. Add this exception to map_sockmap.rst. A listener no longer gets
>-EBUSY from a second map with progs of the same kind.
>
>Since the second commit below, a socket keeps its psock when TCP unhashes
>it. sock_map_link() does not see the state that the socket gets later. Do
>not depend on TCP to keep such a socket out of TCP_LISTEN. Set both
>callbacks in tcp_bpf_clone() to the TCP defaults.
>
>Fixes: 0c48eefae712 ("sock_map: Lift socket state restriction for datagram sockets")
>Fixes: b8b8315e39ff ("bpf, sockmap: Remove unhash handler for BPF sockmap usage")
>Signed-off-by: Chris Mason <mason@kernel.org>
>Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Reviewed-by: John Fastabend <john.fastabend@gmail.com>