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authorKuniyuki Iwashima <kuniyu@amazon.com>2024-07-10 19:12:45 +0200
committerJakub Kicinski <kuba@kernel.org>2024-07-14 00:19:49 +0200
commit23e89e8ee7be73e21200947885a6d3a109a2c58d (patch)
tree0d83add45f01a57bad4865f978d3d88796230d97 /net/ipv4
parenttest/vsock: add install target (diff)
downloadlinux-23e89e8ee7be73e21200947885a6d3a109a2c58d.tar.xz
linux-23e89e8ee7be73e21200947885a6d3a109a2c58d.zip
tcp: Don't drop SYN+ACK for simultaneous connect().
RFC 9293 states that in the case of simultaneous connect(), the connection gets established when SYN+ACK is received. [0] TCP Peer A TCP Peer B 1. CLOSED CLOSED 2. SYN-SENT --> <SEQ=100><CTL=SYN> ... 3. SYN-RECEIVED <-- <SEQ=300><CTL=SYN> <-- SYN-SENT 4. ... <SEQ=100><CTL=SYN> --> SYN-RECEIVED 5. SYN-RECEIVED --> <SEQ=100><ACK=301><CTL=SYN,ACK> ... 6. ESTABLISHED <-- <SEQ=300><ACK=101><CTL=SYN,ACK> <-- SYN-RECEIVED 7. ... <SEQ=100><ACK=301><CTL=SYN,ACK> --> ESTABLISHED However, since commit 0c24604b68fc ("tcp: implement RFC 5961 4.2"), such a SYN+ACK is dropped in tcp_validate_incoming() and responded with Challenge ACK. For example, the write() syscall in the following packetdrill script fails with -EAGAIN, and wrong SNMP stats get incremented. 0 socket(..., SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 3 +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress) +0 > S 0:0(0) <mss 1460,sackOK,TS val 1000 ecr 0,nop,wscale 8> +0 < S 0:0(0) win 1000 <mss 1000> +0 > S. 0:0(0) ack 1 <mss 1460,sackOK,TS val 3308134035 ecr 0,nop,wscale 8> +0 < S. 0:0(0) ack 1 win 1000 +0 write(3, ..., 100) = 100 +0 > P. 1:101(100) ack 1 -- # packetdrill cross-synack.pkt cross-synack.pkt:13: runtime error in write call: Expected result 100 but got -1 with errno 11 (Resource temporarily unavailable) # nstat ... TcpExtTCPChallengeACK 1 0.0 TcpExtTCPSYNChallenge 1 0.0 The problem is that bpf_skops_established() is triggered by the Challenge ACK instead of SYN+ACK. This causes the bpf prog to miss the chance to check if the peer supports a TCP option that is expected to be exchanged in SYN and SYN+ACK. Let's accept a bare SYN+ACK for active-open TCP_SYN_RECV sockets to avoid such a situation. Note that tcp_ack_snd_check() in tcp_rcv_state_process() is skipped not to send an unnecessary ACK, but this could be a bit risky for net.git, so this targets for net-next. Link: https://www.rfc-editor.org/rfc/rfc9293.html#section-3.5-7 [0] Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20240710171246.87533-2-kuniyu@amazon.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net/ipv4')
-rw-r--r--net/ipv4/tcp_input.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index e0f54b9be850..ff9ab3d01ced 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5998,6 +5998,11 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
* RFC 5961 4.2 : Send a challenge ack
*/
if (th->syn) {
+ if (sk->sk_state == TCP_SYN_RECV && sk->sk_socket && th->ack &&
+ TCP_SKB_CB(skb)->seq + 1 == TCP_SKB_CB(skb)->end_seq &&
+ TCP_SKB_CB(skb)->seq + 1 == tp->rcv_nxt &&
+ TCP_SKB_CB(skb)->ack_seq == tp->snd_nxt)
+ goto pass;
syn_challenge:
if (syn_inerr)
TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
@@ -6007,6 +6012,7 @@ syn_challenge:
goto discard;
}
+pass:
bpf_skops_parse_hdr(sk, skb);
return true;
@@ -6813,6 +6819,9 @@ tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
tcp_fast_path_on(tp);
if (sk->sk_shutdown & SEND_SHUTDOWN)
tcp_shutdown(sk, SEND_SHUTDOWN);
+
+ if (sk->sk_socket)
+ goto consume;
break;
case TCP_FIN_WAIT1: {