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net: mptcp: don't hang before sending 'MP capable with data'
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the following packetdrill script

  socket(..., SOCK_STREAM, IPPROTO_MPTCP) = 3
  fcntl(3, F_GETFL) = 0x2 (flags O_RDWR)
  fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
  connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)
  > S 0:0(0) <mss 1460,sackOK,TS val 100 ecr 0,nop,wscale 8,mpcapable v1 flags[flag_h] nokey>
  < S. 0:0(0) ack 1 win 65535 <mss 1460,sackOK,TS val 700 ecr 100,nop,wscale 8,mpcapable v1 flags[flag_h] key[skey=2]>
  > . 1:1(0) ack 1 win 256 <nop, nop, TS val 100 ecr 700,mpcapable v1 flags[flag_h] key[ckey,skey]>
  getsockopt(3, SOL_SOCKET, SO_ERROR, [0], [4]) = 0
  fcntl(3, F_SETFL, O_RDWR) = 0
  write(3, ..., 1000) = 1000

doesn't transmit 1KB data packet after a successful three-way-handshake,
using mp_capable with data as required by protocol v1, and write() hangs
forever:

 PID: 973    TASK: ffff97dd399cae80  CPU: 1   COMMAND: "packetdrill"
  #0 [ffffa9b94062fb78] __schedule at ffffffff9c90a000
  multipath-tcp#1 [ffffa9b94062fc08] schedule at ffffffff9c90a4a0
  multipath-tcp#2 [ffffa9b94062fc18] schedule_timeout at ffffffff9c90e00d
  multipath-tcp#3 [ffffa9b94062fc90] wait_woken at ffffffff9c120184
  multipath-tcp#4 [ffffa9b94062fcb0] sk_stream_wait_connect at ffffffff9c75b064
  multipath-tcp#5 [ffffa9b94062fd20] mptcp_sendmsg at ffffffff9c8e801c
  multipath-tcp#6 [ffffa9b94062fdc0] sock_sendmsg at ffffffff9c747324
  multipath-tcp#7 [ffffa9b94062fdd8] sock_write_iter at ffffffff9c7473c7
  multipath-tcp#8 [ffffa9b94062fe48] new_sync_write at ffffffff9c302976
  multipath-tcp#9 [ffffa9b94062fed0] vfs_write at ffffffff9c305685
 multipath-tcp#10 [ffffa9b94062ff00] ksys_write at ffffffff9c305985
 multipath-tcp#11 [ffffa9b94062ff38] do_syscall_64 at ffffffff9c004475
 multipath-tcp#12 [ffffa9b94062ff50] entry_SYSCALL_64_after_hwframe at ffffffff9ca0008c
     RIP: 00007f959407eaf7  RSP: 00007ffe9e95a910  RFLAGS: 00000293
     RAX: ffffffffffffffda  RBX: 0000000000000008  RCX: 00007f959407eaf7
     RDX: 00000000000003e8  RSI: 0000000001785fe0  RDI: 0000000000000008
     RBP: 0000000001785fe0   R8: 0000000000000000   R9: 0000000000000003
     R10: 0000000000000007  R11: 0000000000000293  R12: 00000000000003e8
     R13: 00007ffe9e95ae30  R14: 0000000000000000  R15: 0000000000000000
     ORIG_RAX: 0000000000000001  CS: 0033  SS: 002b

Fix it ensuring that socket state is TCP_ESTABLISHED on reception of the
third ack.

Fixes: 1954b86 ("mptcp: Check connection state before attempting send")
Suggested-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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@dcaratti @davem330
dcaratti authored and davem330 committed Mar 12, 2020
1 parent dc3e19f commit 767d3de
Showing 1 changed file with 4 additions and 0 deletions.
4 changes: 4 additions & 0 deletions net/mptcp/protocol.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1049,6 +1049,10 @@ void mptcp_finish_connect(struct sock *ssk)
WRITE_ONCE(msk->write_seq, subflow->idsn + 1);
WRITE_ONCE(msk->ack_seq, ack_seq);
WRITE_ONCE(msk->can_ack, 1);
if (inet_sk_state_load(sk) != TCP_ESTABLISHED) {
inet_sk_state_store(sk, TCP_ESTABLISHED);
sk->sk_state_change(sk);
}
}

static void mptcp_sock_graft(struct sock *sk, struct socket *parent)
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