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SubjectRe: plan9 semantics on Linux - mount namespaces
Enrico Weigelt <> writes:

> On 13.02.2018 22:12, Enrico Weigelt wrote:
> CC
>> Hi folks,
>> I'm currently trying to implement plan9 semantics on Linux and
>> yet sorting out how to do the mount namespace handling.
>> On plan9, any unprivileged process can create its own namespace
>> and mount/bind at will, while on Linux this requires CAP_SYS_ADMIN.
>> What is the reason for not allowing arbitrary users to create their
>> own private mount namespace ? What could go wrong here ?

suid root executables could be fooled. An easy case is fooling
/bin/su into reading a different copy of /etc/shadow, and allowing
arbitrary changes between users.

>> IMHO, we could allow mount/bind under the following conditions:
>> * the process is in a private mount namespace
>> * no suid-flag is honored (either force all mounts to nosuid or
>>   completely mask it out)
>> * only certain whitelisted filesystems allowed (eg. 9P and FUSE)
>> Maybe that all could be enabled by a new capability.
>> any suggestions ?

User namespaces limit the contained processes to not having any
permissions outside of the user namespace. While still allowing the
fully unix permission model inside user namespaces.

I am in the final stages of getting the changes in the vfs and in fuse
to allow unprivileged users to mount that filesystem. plan9fs would
also be a candidate for that kind of treatment if it had a maintainer.


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