Thanks Moody for the nudge in a direction I hadn't explored. It seems that Linux does not see 9p as been safe to mount without privilege. From what I understand, only FS with the FS_USERNS_MOUNT flag can be mounted in a user namespace. It seems that v9fs is not one of them:
For example, tmpfs is a safe FS, and I can do: unshare --user --map-root-user --mount mount -t tmpfs tmpfs mnt/mnt1/ and it works. However, if I do: unshare --user --map-root-user --mount mount -t 9p -o trans=unix /run/9p/srv4 mnt/mnt1 I get mount: /home/edouard/mnt/mnt1: permission denied. I've sent an email to the linux kernel mailing list to see if somebody there has any up to date information. Somebody tried the same thing in 2018: https://lore.kernel.org/all/39b08c53-3449-3164-c1b1-44ac587dd...@metux.net/T/ Seemingly without succeeding. The end of the above thread is a bit worrying: > plan9fs would > also be a candidate for that kind of treatment if it had a maintainer. I did not know v9fs was unmaintained, I find that a bit surprising. It does work very reliably. I'll keep this list updated as I make progress. Cheers, Edouard mo...@posixcafe.org writes: > Edouard, > > I am no Linux expert, but I think if you create a mount namespace as part of > the user namespace you will be allowed to execute mounts without root. In > terms of clients, I am not aware > of any other then the one within the linux kernel. > > Regards, > Moody > 9fans / 9fans / see discussions + participants + delivery options Permalink ------------------------------------------ 9fans: 9fans Permalink: https://9fans.topicbox.com/groups/9fans/Tb5d039f675c54046-M7429b33b5dade82a7a13839d Delivery options: https://9fans.topicbox.com/groups/9fans/subscription
