From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from gandalf.ozlabs.org (gandalf.ozlabs.org [150.107.74.76]) by passt.top (Postfix) with ESMTPS id 09E745A0272 for ; Tue, 26 Mar 2024 06:42:33 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gibson.dropbear.id.au; s=202312; t=1711431746; bh=e/IvwLvd4IQJEh7LZPznKR7qZ5/3xYpEhYjKfB+Ys6A=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=FL6GJ12wNUblij9JUNj/vWKhHOSdRz1f58WXqOpKhdE1y0v0mVD35BPp065zhO4NG W0GTLmEXe7tCajBgdaQtdx0i2z6qJGAINEUEkwn7LBWhsU5/puEeGlBfOGC+t5EN1o Q0RgIjHBnoNR3d5/WJM9Iz9OJD3fsPwB2j3ogs07WZAzHwBJHH6Wc8QhPKZncVJdEn aDO85zLgCm1eRQDYz4aU0bsGAhv0IFcVaA9cZbk1lbLu2wlVzl7vGQ9lNJufFXXLXc wyy47NVBBaoczDripSkkPl3Nmr0xpGjslGpgsduZFXSstbBLlL9NJctKgioZqV/2dG PNYPONwDb82tQ== Received: by gandalf.ozlabs.org (Postfix, from userid 1007) id 4V3dwy6M8vz4wxt; Tue, 26 Mar 2024 16:42:26 +1100 (AEDT) From: David Gibson To: passt-dev@passt.top, Stefano Brivio Subject: [PATCH 4/4] tcp: Unconditionally force ACK for all !SYN, !RST packets Date: Tue, 26 Mar 2024 16:42:24 +1100 Message-ID: <20240326054224.716874-5-david@gibson.dropbear.id.au> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20240326054224.716874-1-david@gibson.dropbear.id.au> References: <20240326054224.716874-1-david@gibson.dropbear.id.au> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Message-ID-Hash: IVUAYCFN3JJOVQPFOCJ4A7Y3S7UZKITE X-Message-ID-Hash: IVUAYCFN3JJOVQPFOCJ4A7Y3S7UZKITE X-MailFrom: dgibson@gandalf.ozlabs.org X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: maxi.rostock@outlook.de, pholzing@redhat.com, David Gibson X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: Currently we set ACK on flags packets only when the acknowledged byte pointer has advanced, or we hadn't previously set a window. This means in particular that we can send a window update with no ACK flag, which doesn't appear to be correct. RFC 9293 requires a receiver to ignore such a packet [0], and indeed it appears that every non-SYN, non-RST packet should have the ACK flag. The reason for the existing logic, rather than always forcing an ACK seems to be to avoid having the packet mistaken as a duplicate ACK which might trigger a fast retransmit. However, earlier tests in the function mean we won't reach here if we don't have either an advance in the ack pointer - which will already set the ACK flag, or a window update - which shouldn't trigger a fast retransmit. [0] https://www.ietf.org/rfc/rfc9293.html#section-3.10.7.4-2.5.2.1 Link: https://github.com/containers/podman/issues/22146 Link: https://bugs.passt.top/show_bug.cgi?id=84 Signed-off-by: David Gibson --- tcp.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/tcp.c b/tcp.c index b65ddeb5..28562b7f 100644 --- a/tcp.c +++ b/tcp.c @@ -1593,8 +1593,6 @@ static void tcp_update_seqack_from_tap(const struct ctx *c, */ static int tcp_send_flag(struct ctx *c, struct tcp_tap_conn *conn, int flags) { - uint32_t prev_ack_to_tap = conn->seq_ack_to_tap; - uint32_t prev_wnd_to_tap = conn->wnd_to_tap; struct tcp4_l2_flags_buf_t *b4 = NULL; struct tcp6_l2_flags_buf_t *b6 = NULL; struct tcp_info tinfo = { 0 }; @@ -1675,9 +1673,7 @@ static int tcp_send_flag(struct ctx *c, struct tcp_tap_conn *conn, int flags) *data++ = OPT_WS_LEN; *data++ = conn->ws_to_tap; } else if (!(flags & RST)) { - if (conn->seq_ack_to_tap != prev_ack_to_tap || - !prev_wnd_to_tap) - flags |= ACK; + flags |= ACK; } th->doff = (sizeof(*th) + optlen) / 4; -- 2.44.0