[PATCH v3 00/25] user_namespace: introduce fsid mappings

Serge E. Hallyn serge at hallyn.com
Wed Feb 19 19:35:58 UTC 2020

On Tue, Feb 18, 2020 at 03:33:46PM +0100, Christian Brauner wrote:
> With fsid mappings we can solve this by writing an id mapping of 0
> 100000 100000 and an fsid mapping of 0 300000 100000. On filesystem
> access the kernel will now lookup the mapping for 300000 in the fsid
> mapping tables of the user namespace. And since such a mapping exists,
> the corresponding files will have correct ownership.

So if I have

/proc/self/uid_map: 0 100000 100000
/proc/self/fsid_map: 1000 1000 1

1. If I read files from the rootfs which have host uid 101000, they
will appear as uid 100 to me?

2. If I read host files with uid 1000, they will appear as uid 1000 to me?

3. If I create a new file, as uid 1000, what will be the inode owning uid?

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