x/crypto/ssh: Session.Wait() hangs while reading from msg channel after sending EOF to os.Stdin

[gopherbot]

by mischief@offblast.org:

Hi, I'm using go.crypto/ssh to implement an ssh client. I connected
os.Stdin/Stdout/Stderr to Sesion.Stdin/Stdout/Stderr, allocated a PTY and started a
shell. Sending EOF to stdin will cause Session.Wait() to never return while waiting for
a message or close() on clientChan.msg.

The expected behavior here would be for go.crypto/ssh to catch the EOF from
Session.Stdin, send an eof to the remote side's program. Currently, it seems to just
kill Stdin locally and hang it. It might be that the remote program is not a shell, and
some program like cat. In that case, an EOF would simply stop the remote cat process. If
it were the shell, the shell would quit, and send a channel close message back to
go.crypto/ssh, indicating the session is done.

My program can be seen here:
https://bitbucket.org/mischief/scpu/src/51d57a77fcb4799b99424aac782f4ba061b1df01/scpu.go?at=default

I'm using go tip, and I'm testing this on debian 7 and 9front hosts, and connecting to
an openbsd 5.3 server.

Incriminating backtrace after sending EOF:

gdb$ goroutine 1 bt                                                                     
                                                                                 
#0  0x0000000000417a06 in runtime.park (unlockf=void, lock=void, reason=void) at
/srv/go/src/pkg/runtime/proc.c:1224
#1  0x00000000004055f3 in runtime.chanrecv (c=void, ep=void, selected=void,
received=void) at /srv/go/src/pkg/runtime/chan.c:391
#2  0x0000000000405a75 in runtime.chanrecv2 (t=void, c=void) at
/srv/go/src/pkg/runtime/chan.c:464
#3  0x0000000000432b76 in code.google.com/p/go.crypto/ssh.(*Session).wait
(s=0xc210036770, ~anon0=...) at
/tmp/scpu/src/code.google.com/p/go.crypto/ssh/session.go:415
#4  0x0000000000432a23 in code.google.com/p/go.crypto/ssh.(*Session).Wait
(s=0xc210036770, ~anon0=...) at
/tmp/scpu/src/code.google.com/p/go.crypto/ssh/session.go:397
#5  0x000000000040187c in main.interactive (session=0xc210036770, ~anon1=...) at
/tmp/scpu/src/bitbucket.org/mischief/scpu/scpu.go:99
#6  0x000000000040145a in main.main () at
/tmp/scpu/src/bitbucket.org/mischief/scpu/scpu.go:74
#7  0x0000000000415954 in runtime.main () at /srv/go/src/pkg/runtime/proc.c:182
#8  0x0000000000417bd0 in ?? () at /srv/go/src/pkg/runtime/proc.c:1267
#9  0x0000000000000000 in ?? ()

[robpike]

Comment 1:

Labels changed: added priority-later, removed priority-triage, go1.2maybe.

[robpike]

Comment 2:

Status changed to Accepted.

[hanwen]

Comment 3:

Do you have a self contained example that demonstrates this? in ssh/test/ there is a
framework for writing tests against OpenSSH. I think I have a change that might fix
this, but I'd like to verify.

[hanwen]

Comment 4:

Do you have a self contained example that demonstrates this? in ssh/test/ there is a
framework for writing tests against OpenSSH. I think I have a change that might fix
this, but I'd like to verify.

[rsc]

Comment 5:

Labels changed: added go1.3maybe.

[rsc]

Comment 6:

Labels changed: added release-none, removed go1.3maybe.

[rsc]

Comment 7:

Labels changed: added repo-crypto.

[axw]

Comment 8:

I've just hit this. Repro test case (add to session_test.go, along with import "os"):
http://play.golang.org/p/ENRws4aHYV
After the exec completes, Wait blocks until each stdio goroutine returns. The io.Copy
from the pipe is blocking indefinitely.

[davecheney]

Comment 9:

@axwalk, could you please try the development fork at code.google.com/p/gosshnew/ssh and
see if the problem is fixed there ?

[axw]

Comment 10:

@davecheney, same deal on gosshnew.

[davecheney]

Comment 11:

@axwalk, thanks for confirming.

[axw]

Comment 12:

https://golang.org/cl/45200043/
(Is there a way to automatically link CLs to issues?)

[hanwen]

fixed in https://codereview.appspot.com/50380043 .

this can be closed. @ianlancetaylor