Cannot access mounted pts device inside container

[codeaholics]

• [x] This is a bug report
• [ ] This is a feature request
• [x] I searched existing issues before opening this one

Expected behavior

Mounting a pts device with --device should make it accessible within the container.

Actual behavior

The device appears, but I get EIO when trying to access it.

Steps to reproduce the behavior

I am using socat to bring a remote serial port to my server over the LAN. socat creates pts devices.

On the physical machine:

root@server:~# ls -l /dev/pts/1
crw--w---- 1 root tty 136, 1 Aug  3 20:54 /dev/pts/1
root@server:~# cat /dev/pts/1
[...output from remote serial device...]

Start a container:

docker run -ti --device=/dev/pts/1:/dev/hostpts ubuntu:17.04 /bin/bash

Now, inside the container:

root@689d0696b167:/# ls -l /dev/hostpts
crw--w---- 1 root tty 136, 1 Aug  3 20:02 /dev/hostpts
root@689d0696b167:/# cat /dev/hostpts
cat: /dev/hostpts: Input/output error

Trying with /dev/null instead of a pts appears to work fine:

root@server:~# docker run -ti --device=/dev/null:/dev/hostnull ubuntu:17.04 /bin/bash
root@2b75680ed7a9:/# ls -l /dev/hostnull
crw-rw-rw- 1 root root 1, 3 Aug  3 20:03 /dev/hostnull
root@2b75680ed7a9:/# cat /dev/hostnull
root@2b75680ed7a9:/#

Output of docker version:

Client:
 Version:      17.06.0-ce
 API version:  1.30
 Go version:   go1.8.3
 Git commit:   02c1d87
 Built:        Fri Jun 23 21:18:10 2017
 OS/Arch:      linux/amd64

Server:
 Version:      17.06.0-ce
 API version:  1.30 (minimum version 1.12)
 Go version:   go1.8.3
 Git commit:   02c1d87
 Built:        Fri Jun 23 21:17:03 2017
 OS/Arch:      linux/amd64
 Experimental: false

Output of docker info:

Containers: 21
 Running: 3
 Paused: 0
 Stopped: 18
Images: 56
Server Version: 17.06.0-ce
Storage Driver: aufs
 Root Dir: /var/lib/docker/aufs
 Backing Filesystem: extfs
 Dirs: 78
 Dirperm1 Supported: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
 Volume: local
 Network: bridge host macvlan null overlay
 Log: awslogs fluentd gcplogs gelf journald json-file logentries splunk syslog
Swarm: inactive
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: cfb82a876ecc11b5ca0977d1733adbe58599088a
runc version: 2d41c047c83e09a6d61d464906feb2a2f3c52aa4
init version: 949e6fa
Security Options:
 apparmor
 seccomp
  Profile: default
Kernel Version: 4.10.0-26-generic
Operating System: Ubuntu 17.04
OSType: linux
Architecture: x86_64
CPUs: 4
Total Memory: 15.55GiB
Name: server
ID: MME7:KAO3:HFB7:RCTP:4P45:FWLV:TI46:YLYQ:3INW:7MLD:LZ2Y:BJK3
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): false
Username: codeaholics
Registry: https://index.docker.io/v1/
Experimental: false
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false

WARNING: No swap limit support

Additional environment details (AWS, VirtualBox, physical, etc.)

root@server:~# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 17.04
Release:    17.04
Codename:   zesty
root@server:~# uname -a
Linux server 4.10.0-26-generic #30-Ubuntu SMP Tue Jun 27 09:30:12 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

[codeaholics]

I've also tried with --security-opt seccomp=unconfined --security-opt apparmor=unconfined and that doesn't change the behaviour.

--privileged causes the device not to appear in the container at all!

[thaJeztah]

Sounds related to https://github.com/moby/moby/issues/11462 (which explains a bit what happens when you start a container)

[plouj]

I can still reproduce this in Docker version 18.05.0-ce, build f150324:

plouj@host:~$ socat -ddd PTY,link=/tmp/remote-serial,rawer,wait-slave,b19200,mode=666 - &
plouj@host:~$ docker run -it --rm --device=/tmp/remote-serial:/dev/ttyUSB0:rwm ubuntu:17.10 /bin/bash
root@5e18766143c9:/# apt update && apt install minicom && minicom --device /dev/ttyUSB0
[...]
minicom: cannot open /dev/ttyUSB0: Input/output error

- stracing minicom in the container (via its parent bash process) from the outside host reveals:

[pid 13507] openat(AT_FDCWD, "/dev/ttyUSB0", O_RDWR|O_NOCTTY|O_NONBLOCK) = -1 EIO (Input/output error)

[kungfoolfighting]

@codeaholics I am trying to do the exact same thing, did you ever get it to work? If not this way, what was your workaround?

[codeaholics]

No, I didn’t. The software inside the container is open source, so I patched it to work with either serial or TCP and had it reach out directly to the socat on the far end without needing one on the local end.

On 28 May 2018, at 14:57, kungfoolfighting notifications@github.com wrote:

@codeaholics I am trying to do the exact same thing, did you ever get it to work? If not this way, what was your workaround?

— You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub, or mute the thread.

[coolacid]

For those that come across this I may have found a work around, one can simply use a volume mount to bindmount the FD into the container.

socat -d -d pty,raw,echo=0,link=/dev/ttyV1 udp4-listen:5000,reuseaddr

docker run -ti --volume=/dev/ttyV1:/dev/ttyV1 ubuntu:17.04 /bin/bash
root@d354ff3eb411:/# ls /dev/ -l
total 0
crw--w---- 1 root tty  136, 0 Jan 23 04:23 console
lrwxrwxrwx 1 root root     11 Jan 23 04:23 core -> /proc/kcore
lrwxrwxrwx 1 root root     13 Jan 23 04:23 fd -> /proc/self/fd
crw-rw-rw- 1 root root   1, 7 Jan 23 04:23 full
drwxrwxrwt 2 root root     40 Jan 23 04:23 mqueue
crw-rw-rw- 1 root root   1, 3 Jan 23 04:23 null
lrwxrwxrwx 1 root root      8 Jan 23 04:23 ptmx -> pts/ptmx
drwxr-xr-x 2 root root      0 Jan 23 04:23 pts
crw-rw-rw- 1 root root   1, 8 Jan 23 04:23 random
drwxrwxrwt 2 root root     40 Jan 23 04:23 shm
lrwxrwxrwx 1 root root     15 Jan 23 04:23 stderr -> /proc/self/fd/2
lrwxrwxrwx 1 root root     15 Jan 23 04:23 stdin -> /proc/self/fd/0
lrwxrwxrwx 1 root root     15 Jan 23 04:23 stdout -> /proc/self/fd/1
crw-rw-rw- 1 root root   5, 0 Jan 23 04:23 tty
crw--w---- 1 root tty  136, 9 Jan 23 04:22 ttyV1
crw-rw-rw- 1 root root   1, 9 Jan 23 04:23 urandom
crw-rw-rw- 1 root root   1, 5 Jan 23 04:23 zero
root@d354ff3eb411:/# cat /dev/ttyV1
Hello all

echo "Hello all" | nc -u localhost 5000

Keep in mind, if the pty goes away and is re-created, the container will not know any better and EIO any access to it

[Teawolf-beep]

Still not working in 19.03.8-ce build afacb8b7f0...however the workaround to use the pts device via the volume flag as mentioned by coolacid seems to work for now.

[kamiccolo]

Still an issue as of 24.0.5, build ced0996600

Even explicitly adding to the cgroup:

$ stat -c "%Hr %Lr" /dev/pts/4
136 4

docker run --rm --device-cgroup-rule='c 136:* rmw' --device=/dev/pts/5:/dev/my_fancy_device  -i -t my_fancy_container /bin/bash

cat /dev/my_fancy_device
cat /dev/my_fancy_device: Input/output error