Hello,
as an unprivileged user one is able to keep network namespaces from expiring by opening /proc/<pid>/net/dev of other processes. I've previously put this on stackexchange [1] and then bugzilla [2]. That's been a while though, so posting here for a bit more visibility in case it's something that's worth fixing.
The reproducer is roughly as follows. As root:
# echo "100" > /proc/sys/user/max_net_namespaces
# while true ; do (unshare -n bash -c 'sleep 0.3 && readlink /proc/self/ns/net') || sleep 0.5 ; done
As unprivileged user in a second terminal, run the below Python script [3]:
# python3 pin_net_namespaces.py
After about one minute the first terminal will show the following until the Python process keeping the network namespaces alive is terminated.
...
unshare: unshare failed: No space left on device
unshare: unshare failed: No space left on device
unshare: unshare failed: No space left on device
unshare: unshare failed: No space left on device
Without the change to max_net_namespaces reproducing just very long, but then also kernel memory grows fairly large.
Does that seem like problematic behavior? I had attached a patch and tests to [2], but I fall into the kernel newbie category, so not sure how useful.
Thanks,
Arne
[3] $ cat pin_net_namespaces.py
#!/usr/bin/env python3
import glob
import os
import time
net_namespaces = {}
while True:
for net_dev in glob.glob("/proc/*/net/dev"):
try:
ino = os.stat(net_dev).st_ino
if ino not in net_namespaces:
net_namespaces[ino] = open(net_dev)
print("Have", len(net_namespaces), "namespaces...")
except FileNotFoundError:
# not fast enough...
pass
time.sleep(0.2)
import glob
import os
import time
net_namespaces = {}
while True:
for net_dev in glob.glob("/proc/*/net/dev"):
try:
ino = os.stat(net_dev).st_ino
if ino not in net_namespaces:
net_namespaces[ino] = open(net_dev)
print("Have", len(net_namespaces), "namespaces...")
except FileNotFoundError:
# not fast enough...
pass
time.sleep(0.2)
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