Public bug reported:
It seems that if-up.d is activated before any temporary directory is
available. On affected setup that caused a bash here-tag to fail, thus
security settings were not applied to the interface leaving it open to
attacks.
Documentation seems to be unclear, if any script should expect, that
temporary directory would work. At least here it was quite unexpected
that data processing in scripts without explicit request for disk
operation failed due to that.
In my opinion, a CAVEAT in the interfaces (5) documentation might be
sufficient in most cases.
A workaround for the affected setup was to create a separate temporary
directory on /var/run (which is a tmpfs instance) and export it using
TEMPDIR.
To reproduce:
cat <<OUTEREOF > /etc/network/if-up.d/aaa-early
#!/bin/bash
echo "mounts"
cat /proc/mounts
echo "touch"
touch /tmp/xxx
cat <<EOF
Here document test
EOF
echo "mounts again"
cat /proc/mounts
OUTEREOF
chmod 0755 /etc/network/if-up.d/aaa-early
touch /forcefsck
reboot
# cat /var/log/upstart/network-interface-eth0.log
mounts
...
tmpfs /run tmpfs rw,nosuid,noexec,relatime,size=24784k,mode=755 0 0
/dev/disk/by-uuid/19c0ddc6-c305-4a8a-86f2-fb470ae5b39c / ext4
ro,relatime,data=ordered 0 0
...
touch
touch: cannot touch '/tmp/xxx': Read-only file system
/etc/network/if-up.d/aaa-early: line 7: cannot create temp file for
here-document: Read-only file system
mounts again
...
/dev/disk/by-uuid/19c0ddc6-c305-4a8a-86f2-fb470ae5b39c / ext4
ro,relatime,data=ordered 0 0
...
# lsb_release -rd
Description: Ubuntu 14.04.2 LTS
Release: 14.04
# apt-cache policy ifupdown
ifupdown:
Installed: 0.7.47.2ubuntu4.1
Candidate: 0.7.47.2ubuntu4.1
Version table:
*** 0.7.47.2ubuntu4.1 0
500 http://ubuntu-proxy-ehealth.d03.arc.local/ubuntu/
trusty-updates/main i386 Packages
100 /var/lib/dpkg/status
0.7.47.2ubuntu4 0
500 http://ubuntu-proxy-ehealth.d03.arc.local/ubuntu/ trusty/main i386
Packages
** Affects: ifupdown (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1434121
Title:
if-up might fail when triggered before temporary directory available
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