diff options
| author | Kuniyuki Iwashima <kuniyu@amazon.com> | 2024-07-10 10:12:45 -0700 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2024-07-13 15:19:49 -0700 |
| commit | 23e89e8ee7be73e21200947885a6d3a109a2c58d (patch) | |
| tree | 0d83add45f01a57bad4865f978d3d88796230d97 | |
| parent | 42ffe242860c401c34c62aa369c2add341a6eece (diff) | |
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>
| -rw-r--r-- | net/ipv4/tcp_input.c | 9 |
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: { |