Does ssh need sendfd in pledge() call?

[Timothy Brown]

Hi,

I posted this question to the OpenBSD bugs list last week, however
I have had no reply and it was suggested on IRC that I post here
instead. So I must apologise if this is not appropriate.

For a reference here is my previous post:
https://marc.info/?l=openbsd-bugs&m=156080681530337&w=2

I am running OpenBSD 6.5-stable (also tested on -current). When I
ssh somewhere I get a sig abort from pledge().

I use a Yubikey with GPG and use gpg-agent as my ssh-agent. I also
remote forawrd this agent. For example my .ssh/config has the following
(please note the RemoteForward is actually all on one line, I have split
it here to keep it below 80 chars):

Host www
  Hostname 192.168.1.100
  RemoteForward /home/tbrown/.gnupg/S.gpg-agent \
                /home/tbrown/.gnupg/S.gpg-agent.extra
  ExitOnForwardFailure yes

Host *
  ForwardX11 no
  Compression yes
  ServerAliveInterval 30
  ServerAliveCountMax 4
  ControlMaster auto
  ControlPath ~/.ssh/mux/%h_%p_%r
  ControlPersist 4h

If I ssh, for example:

xps ~$ ssh www
Abort trap (core dumped)
xps ~$

I have attached output for when I crank up there verbosity (ssh_verbose.txt),
as it contains long lines.

Dmesg contains:

sh[28960]: pledge "sendfd", syscall 28

If I `ktrace` ssh, I get the following:
 28960 ssh      PLDG  sendmsg, "sendfd", errno 1 Operation not permitted
 28960 ssh      PSIG  SIGABRT SIG_DFL
 28960 ssh      NAMI  "ssh.core"

If I add sendfd to the pledge() call, it works. Please see the attached
patch (ssh.patch).  However I do not know if this is an acceptable
solution.

I guess I have to ask if I am doing something wrong? As in I thought I
would not be the first to hit this error.

Does anybody have any thoughts or ideas?

Many thanks.
Timothy
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Authenticated to 192.168.1.100 ([192.168.1.100]:22).
debug1: Remote connections from /home/tbrown/.gnupg/S.gpg-agent:-2 forwarded to local address /home/tbrown/.gnupg/S.gpg-agent.extra:-2
debug3: send packet: type 80
debug1: setting up multiplex master socket
debug3: muxserver_listen: temporary control path /home/tbrown/.ssh/mux/192.168.1.100_22_tbrown.2EvGYCjVoPNdAIrh
debug2: fd 4 setting O_NONBLOCK
debug3: fd 4 is O_NONBLOCK
debug3: fd 4 is O_NONBLOCK
debug1: channel 0: new [/home/tbrown/.ssh/mux/192.168.1.100_22_tbrown]
debug3: muxserver_listen: mux listener channel 0 fd 4
debug2: fd 3 setting TCP_NODELAY
debug3: ssh_packet_set_tos: set IP_TOS 0x20
debug1: deferring postauth fork until remote forward confirmation received
debug1: Entering interactive session.
debug1: pledge: id
debug2: set_control_persist_exit_time: schedule exit in 14400 seconds
debug3: receive packet: type 80
debug1: client_input_global_request: rtype hostkeys-00 at openssh.com want_reply 0
debug3: receive packet: type 4
debug1: Remote: /home/tbrown/.ssh/authorized_keys:1: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding
debug3: receive packet: type 4
debug1: Remote: /home/tbrown/.ssh/authorized_keys:1: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding
debug3: receive packet: type 81
debug1: remote forward success for: listen /home/tbrown/.gnupg/S.gpg-agent:-2, connect /home/tbrown/.gnupg/S.gpg-agent.extra:-2
debug1: All remote forwarding requests processed
debug1: control_persist_detach: backgrounding master process
debug2: control_persist_detach: background process is 85607
debug2: fd 4 setting O_NONBLOCK
debug1: forking to background
debug1: multiplexing control connection
debug3: fd 5 is O_NONBLOCK
debug3: fd 5 is O_NONBLOCK
debug1: channel 1: new [mux-control]
debug3: channel_post_mux_listener: new mux channel 1 fd 5
debug3: mux_master_read_cb: channel 1: hello sent
debug2: set_control_persist_exit_time: cancel scheduled exit
debug3: mux_master_read_cb: channel 1 packet type 0x00000001 len 4
debug2: mux_master_process_hello: channel 1 slave version 4
debug2: mux_client_hello_exchange: master version 4
debug3: mux_client_forwards: request forwardings: 0 local, 1 remote
debug1: Requesting forwarding of remote forward /home/tbrown/.gnupg/S.gpg-agent:-2 -> /home/tbrown/.gnupg/S.gpg-agent.extra:-2
debug3: mux_master_read_cb: channel 1 packet type 0x10000006 len 92
debug2: mux_master_process_open_fwd: channel 1: request remote forward /home/tbrown/.gnupg/S.gpg-agent:-2 -> /home/tbrown/.gnupg/S.gpg-agent.extra:-2
debug2: mux_master_process_open_fwd: found existing forwarding
debug3: mux_client_request_session: entering
debug3: mux_client_request_alive: entering
debug3: mux_master_read_cb: channel 1 packet type 0x10000004 len 4
debug2: mux_master_process_alive_check: channel 1: alive check
debug3: mux_client_request_alive: done pid = 806
debug3: mux_master_read_cb: channel 1 packet type 0x10000002 len 57
debug2: mux_master_process_new_session: channel 1: request tty 1, X 0, agent 0, subsys 0, term "rxvt-unicode-256color", cmd "", env 0
debug3: mm_receive_fd: recvmsg: Resource temporarily unavailable
mm_receive_fd: recvmsg: expected received 1 got 0
mux_master_process_new_session: failed to receive fd 0 from slave
debug1: channel 1: mux_rcb failed
debug2: channel 1: zombie
debug2: channel 1: gc: notify user
debug3: mux_master_control_cleanup_cb: entering for channel 1
debug2: channel 1: gc: user detached
debug2: channel 1: zombie
debug2: channel 1: garbage collecting
debug1: channel 1: free: mux-control, nchannels 2
debug3: channel 1: status: The following connections are open:

debug2: set_control_persist_exit_time: schedule exit in 14400 seconds
Abort trap (core dumped)
xps ~$

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