path: root/mm/memcontrol.c
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authorChristian Brauner <>2021-01-21 14:19:20 +0100
committerChristian Brauner <>2021-01-24 14:27:15 +0100
commita6435940b62f81a1718bf2bd46a051379fc89b9d (patch)
treeef8c19f17e540a33c427df827fd8baacf759405c /mm/memcontrol.c
parent19c329f6808995b142b3966301f217c831e7cf31 (diff)
mount: attach mappings to mounts
In order to support per-mount idmappings vfsmounts are marked with user namespaces. The idmapping of the user namespace will be used to map the ids of vfs objects when they are accessed through that mount. By default all vfsmounts are marked with the initial user namespace. The initial user namespace is used to indicate that a mount is not idmapped. All operations behave as before. Based on prior discussions we want to attach the whole user namespace and not just a dedicated idmapping struct. This allows us to reuse all the helpers that already exist for dealing with idmappings instead of introducing a whole new range of helpers. In addition, if we decide in the future that we are confident enough to enable unprivileged users to setup idmapped mounts the permission checking can take into account whether the caller is privileged in the user namespace the mount is currently marked with. Later patches enforce that once a mount has been idmapped it can't be remapped. This keeps permission checking and life-cycle management simple. Users wanting to change the idmapped can always create a new detached mount with a different idmapping. Add a new mnt_userns member to vfsmount and two simple helpers to retrieve the mnt_userns from vfsmounts and files. The idea to attach user namespaces to vfsmounts has been floated around in various forms at Linux Plumbers in ~2018 with the original idea tracing back to a discussion in 2017 at a conference in St. Petersburg between Christoph, Tycho, and myself. Link: Cc: Christoph Hellwig <> Cc: David Howells <> Cc: Al Viro <> Cc: Reviewed-by: Christoph Hellwig <> Signed-off-by: Christian Brauner <>
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