How to exemplify this shortcoming of rootless podman: "When using --net=host with rootless containers, subsequent podman execs ..." #23823

eriksjolund · 2024-08-31T14:39:20Z

eriksjolund
Aug 31, 2024

In the list Shortcomings of Rootless Podman there is this sentence:

When using --net=host with rootless containers, subsequent podman execs to that container will not join the host network namespace because it is owned by root.

Does anyone have an example showing this?

I tried it out on Fedora CoreOS 40.20240825.1.0 but I am not able to demonstrate it.
On the other hand I don't know exactly what is meant.

Here is my best trial

Create directory
```
mkdir ~/dir
```
Change directory
```
cd ~/dir
```
Create the file Containerfile containing
```
FROM docker.io/library/fedora
RUN useradd test
```
(user test then has UID 1000 and GID 1000)
Build the container
```
podman build -t myimg .
```

Create the file ~/start.bash containing

#!/bin/bash
set -o errexit
set -o nounset
dir=$(mktemp -d)
touch $dir/file
chmod 777 -R $dir

ctr=$(podman run  --rm -d -v $dir:/dir:z --network=host localhost/myimg sh -c "ls -ln /proc/self/ns/net >> /dir/file && sleep 300")
sleep 1
podman exec --user 1000:1000 $ctr sh -c "ls -ln /proc/self/ns/net >> /dir/file"
podman exec --user 1000:1000 $ctr sh -c "curl -sL www.kernel.org | head -1 >> /dir/file"
echo result:
cat $dir/file

Run the script

bash start.bash

The following output is printed

result:
lrwxrwxrwx. 1 0 0 0 Aug 31 10:15 /proc/self/ns/net -> net:[4026531840]
lrwxrwxrwx. 1 1000 1000 0 Aug 31 10:15 /proc/self/ns/net -> net:[4026531840]
<!DOCTYPE html>

(I don't know how to interpret the results)

For details, see

podman/rootless.md

Line 47 in ef905ef

    
           * When using --net=host with rootless containers, subsequent podman execs to that container will not join the host network namespace because it is owned by root.

eriksjolund · 2024-08-31T14:47:27Z

eriksjolund
Aug 31, 2024
Author

I found a clue

The git commit message
9de18a1
says it fixes
#4473
which has a section Steps to reproduce the issue:

1 reply

eriksjolund Aug 31, 2024
Author

After reading #4473 and #10384 I'm beginning understand what this is all about. I'll close this discussion thread.

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