Re: [PATCH bpf] bpf, sockmap: Account for receive queue in FIONREAD without a verdict program

["Emil Tsalapatis" <emil@etsalapatis.com>]

On Tue Jul 7, 2026 at 12:15 PM EDT, Mattia Meleleo via B4 Relay wrote:
> From: Mattia Meleleo <mattia.meleleo@coralogix.com>
>
> tcp_bpf_ioctl() answers SIOCINQ from psock->msg_tot_len, which only
> counts bytes in ingress_msg. Without a stream/skb verdict program
> nothing is diverted there: data stays in sk_receive_queue, so FIONREAD
> returns 0 even though read() returns data.
>
> Add tcp_inq() to the reported value when the psock has no verdict
> program. The two queues are disjoint, so bytes redirected into
> ingress_msg from other sockets stay correctly accounted through
> msg_tot_len.
>
> Add a selftest covering FIONREAD without a verdict program.
>
> Fixes: 929e30f93125 ("bpf, sockmap: Fix FIONREAD for sockmap")
> Signed-off-by: Mattia Meleleo <mattia.meleleo@coralogix.com>

Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>

I don't think the Sashiko READ_ONCE() recommendation is that important,
we're just checking for the pointers' existence and I don't see how the
reads can be moved/optimized out/merged in a way that breaks this code.

> ---
>  net/ipv4/tcp_bpf.c                                 | 16 ++++++++-
>  .../selftests/bpf/prog_tests/sockmap_basic.c       | 39 ++++++++++++++++++++++
>  2 files changed, 54 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
> index cc0bd73f3..a001b1fff 100644
> --- a/net/ipv4/tcp_bpf.c
> +++ b/net/ipv4/tcp_bpf.c
> @@ -334,6 +334,7 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk,
>  
>  static int tcp_bpf_ioctl(struct sock *sk, int cmd, int *karg)
>  {
> +	struct sk_psock *psock;
>  	bool slow;
>  
>  	if (cmd != SIOCINQ)
> @@ -344,7 +345,20 @@ static int tcp_bpf_ioctl(struct sock *sk, int cmd, int *karg)
>  		return -EINVAL;
>  
>  	slow = lock_sock_fast(sk);
> -	*karg = sk_psock_msg_inq(sk);
> +	psock = sk_psock_get(sk);
> +	if (unlikely(!psock)) {
> +		unlock_sock_fast(sk, slow);
> +		return tcp_ioctl(sk, cmd, karg);
> +	}
> +	*karg = sk_psock_get_msg_len_nolock(psock);
> +	/* Without a verdict program, ingress data is never diverted to
> +	 * ingress_msg: it stays in sk_receive_queue and is read through
> +	 * the fallback to tcp_recvmsg(), so account for it like
> +	 * tcp_ioctl() does.
> +	 */
> +	if (!psock->progs.stream_verdict && !psock->progs.skb_verdict)
> +		*karg += tcp_inq(sk);
> +	sk_psock_put(sk, psock);
>  	unlock_sock_fast(sk, slow);
>  
>  	return 0;
> diff --git a/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c b/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c
> index cb3229711..f0f368201 100644
> --- a/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c
> +++ b/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c
> @@ -1373,6 +1373,43 @@ static void test_sockmap_multi_channels(int sotype)
>  	test_sockmap_pass_prog__destroy(skel);
>  }
>  
> +/* A socket in a sockmap without a verdict program keeps its ingress data
> + * in sk_receive_queue: FIONREAD must account for it.
> + */
> +static void test_sockmap_no_verdict_fionread(void)
> +{
> +	int err, map, zero = 0, sent, avail;
> +	int c0 = -1, c1 = -1, p0 = -1, p1 = -1;
> +	struct test_sockmap_pass_prog *skel;
> +	char buf[256] = "0123456789";
> +
> +	skel = test_sockmap_pass_prog__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "open_and_load"))
> +		return;
> +	map = bpf_map__fd(skel->maps.sock_map_rx);
> +
> +	err = create_socket_pairs(AF_INET, SOCK_STREAM, &c0, &c1, &p0, &p1);
> +	if (!ASSERT_OK(err, "create_socket_pairs()"))
> +		goto out;
> +
> +	err = bpf_map_update_elem(map, &zero, &c1, BPF_NOEXIST);
> +	if (!ASSERT_OK(err, "bpf_map_update_elem(c1)"))
> +		goto out_close;
> +
> +	sent = xsend(p1, &buf, sizeof(buf), 0);
> +	ASSERT_EQ(sent, sizeof(buf), "xsend(p1)");
> +	avail = wait_for_fionread(c1, sizeof(buf), IO_TIMEOUT_SEC);
> +	ASSERT_EQ(avail, sizeof(buf), "ioctl(FIONREAD)");
> +
> +out_close:
> +	close(c0);
> +	close(p0);
> +	close(c1);
> +	close(p1);
> +out:
> +	test_sockmap_pass_prog__destroy(skel);
> +}
> +
>  void test_sockmap_basic(void)
>  {
>  	if (test__start_subtest("sockmap create_update_free"))
> @@ -1415,6 +1452,8 @@ void test_sockmap_basic(void)
>  		test_sockmap_skb_verdict_shutdown();
>  	if (test__start_subtest("sockmap skb_verdict fionread"))
>  		test_sockmap_skb_verdict_fionread(true);
> +	if (test__start_subtest("sockmap no_verdict fionread"))
> +		test_sockmap_no_verdict_fionread();
>  	if (test__start_subtest("sockmap skb_verdict fionread on drop"))
>  		test_sockmap_skb_verdict_fionread(false);
>  	if (test__start_subtest("sockmap skb_verdict change tail"))
>
> ---
> base-commit: d2c9a99135da931377240942d44f3dea104cedb8
> change-id: 20260707-fionread-no-verdict-a4f8697ac9f9
>
> Best regards,
> --  
> Mattia Meleleo <mattia.meleleo@coralogix.com>