Bug#859003: systemd-container: strange permissions on /dev/pts/ptmx

Russell Coker russell at coker.com.au
Wed Mar 29 14:07:47 BST 2017

Package: systemd-container
Version: 232-22
Severity: normal

# grep pts /proc/mounts 
devpts /dev/pts devpts rw,seclabel,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000 0 0
# ls -l /dev/pts/ptmx
c---------. 1 root root 5, 2 Mar 20 21:51 /dev/pts/ptmx

The above is from a regular Debian/unstable shell.

# grep pts /proc/mounts 
devpts /dev/pts devpts rw,seclabel,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=666 0 0
# ls -l /dev/pts/ptmx
crw-rw-rw-. 1 root root 5, 2 Mar 30  2017 /dev/pts/ptmx

The above is from a shell run from a chroot managed by systemd-nspawn.  I have
systemd-nspawn starting the below shell script that runs sshd, so nothing in
the chroot environment has any effect on mount options.

Why does the virtual environment created by systemd-nspawn have different
permissions for /dev/pts/ptmx than the outside environment?  I am not claiming
that what systemd-nspawn is doing is inherently wrong (it might be the correct
thing for other distributions), but I believe that it should be consistent with
the main Debian environment.  It is plausible that systemd-nspawn is correct
here and the rest of Debian is wrong, if so please reassign the bug
appropriately.  But as a security person I'm leaning towards minimum privileges
being the correct choice, which means mode 0 would be correct and mode 666
(as used by systemd-nspawn) would be a bug.

set -e

restorecon -R /dev
mkdir -p /var/run/sshd
restorecon -R /var/run
/usr/sbin/sshd -D

-- System Information:
Debian Release: 9.0
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.9.0-2-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_AU.UTF-8, LC_CTYPE=en_AU.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash
Init: systemd (via /run/systemd/system)

Versions of packages systemd-container depends on:
ii  dbus             1.10.16-1
ii  libacl1          2.2.52-3+b1
ii  libblkid1        2.29.2-1
ii  libbz2-1.0       1.0.6-8.1
ii  libc6            2.24-9
ii  libcurl3-gnutls  7.52.1-3
ii  libgcrypt20      1.7.6-1
ii  libip4tc0        1.6.0+snapshot20161117-5
ii  liblzma5         5.2.2-1.2+b1
ii  libseccomp2      2.3.1-2.1
ii  libselinux1      2.6-3+b1
ii  systemd          232-22
ii  zlib1g           1:1.2.8.dfsg-5

Versions of packages systemd-container recommends:
ii  btrfs-progs        4.9.1-1
pn  libnss-mymachines  <none>

systemd-container suggests no packages.

-- no debconf information

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