[RFC PATCH 00/27] Containers and using authenticated filesystems

David Howells
2019-02-15T16:07:25Z

Here's a collection of patches that containerises the kernel keys and makes
it possible to separate keys by namespace. This can be extended to any
filesystem that uses request_key() to obtain the pertinent authentication
token on entry to VFS or socket methods.

I have this working with AFS and AF_RXRPC so far, but it could be extended
to other filesystems, such as NFS and CIFS.

The following changes are made:

(1) Add optional namespace tags to a key's index_key. This allows the
following:

(a) Automatic invalidation of all keys with that tag when the
namespace is removed.

(b) Mixing of keys with the same description, but different areas of
operation within a keyring.

(c) Sharing of cache keyrings, such as the DNS lookup cache.

(d) Diversion of upcalls based on namespace criteria.

(2) Provide each network namespace with a tag that can be used with (1).
This is used by the DNS query, rxrpc, nfs idmapper keys.

[!] Note that it might still be better to move these keyrings into the
network namespace.

(3) Provide key ACLs. These allow:

(a) The permissions can be split more finely, in particular separating
out Invalidate and Join.

(b) Permits to be granted to non-standard subjects. So, for instance,
Search permission could be granted to a container object, allowing
a search of the container keyring by a denizen of the container to
find a key that they can't otherwise see.

(4) Provide a kernel container object. Currently, this is created with a
system call and passed flags that indicate the namespaces to be
inherited or replaced. It might be better to actually use something
like fsconfig() to configure the container by setting key=val type
options.

The kernel container object provides the following facilities:

(a) request_key upcall interception. The manager of a container can
intercept requests made inside the container and, using a series
of filters, can cause the authkeys to be placed into keyrings that
serve as queues for one or more upcall processing programs. These
upcall programs use key notifications to monitor those keyrings.

(b) Per-container keyring. A keyring can be attached to the container
such that this is searched by a request_key() performed by a
denizen of the container after searching the thread, process and
session keyrings. The keyring and the keys contained therein must
be granted Search for that container.

This allows:

(i) Authenticated filesystems to be used transparently inside of
the container without any cooperation from the occupant
thereof. All the key maintenance can be done by the manager.

(ii) Keys to be made available to the denizens of a container (by
granting extra permissions to the container subject).

(c) Per-container ID that can be used in audit messages.

(d) Container object creation gives the manager a file descriptor that
can:

(i) Be passed to a dirfd parameter to a VFS syscall, such as
mkdirat(), allowing an operation to be done inside the
container.

(ii) Be passed to fsopen()/fsconfig() to indicate that the target
filesystem is going to be created inside a container, in that
container's namespaces.

(iii) Be passed to the move_mount() syscall as a destination for
setting the root filesystem inside a new mount namespace made
upon container creation.

(e) The ability to configure the container with namespaces or
whatever, and then fork a process into that container to 'boot'
it.

Three sample programs are provided:

(1) test-container. This:

- Creates a kernel container with a blank mount ns.
- Creates its root mount and moves it to the container root.
- Mounts /proc therein.
- Creates a keyring called "_container"
- Sets that as the container keyring.
- Grants Search permission to the container on that keyring.
- Removes owner permission on that keyring.
- Creates a sample user key "foobar" in the container keyring.
- Grants various permissions to the container on that key.
- Creates a keyring called "upcall"
- Intercepts "user" key upcalls from the container to there.
- Forks a process into the container
- Prints the container keyring ID if it can
- Exec's bash.

This program expects to be given the device name for a partition it
can mount as the root and expects it to contain things like /etc,
/bin, /sbin, /lib, /usr containing programs that can be run and /proc
to mount procfs upon. E.g.:

./test-container /dev/sda3

(2) test-upcall. This is a service program that monitors the "upcall"
keyring created by test-container for authkeys appearing, which it
then hands off to /sbin/request-key. This:

- Opens /dev/watch_queue.
- Sets the size to 1 page.
- Sets a filter to watch for "Link creation" key events.
- Sets a watch on the upcall keyring.
- Polls the watch queue for events
- When an event comes in:
- Gets the authkey ID from the event buffer.
- Queries the authkey.
- Forks of a handler which:
- Moves the authkey to its thread keyring
- Sets up a new session keyring with the authkey in it.
- Execs /sbin/request-key.

This can be run in a shell that shares the session keyring with
test-container, from which it will find the upcall keyring.
Alternatively, the keyring ID can be provided on the command line:

./test-upcall [<upcall-keyring>]

It can be triggered from inside of the container with something like:

keyctl request2 user debug:e a @s

and something like:

ptrs h=4 t=2 m=2000003
NOTIFY[00000004-00000002] ty=0003 sy=0002 i=01000010
KEY 78543393 change=2 aux=141053003
Authentication key 141053003
- create 779280685
- uid=0 gid=0
- rings=0,0,798528519
- callout='a'
RQDebug keyid: 779280685
RQDebug desc: debug:e
RQDebug callout: a
RQDebug session keyring: 798528519

will appear on stdout/stderr from it and /sbin/request-key.

(3) test-cont-grant. This is a program to make the nominated key
available to a container's denizens. It:

- Grants search permission to the nominated key.
- Links the nominated key into the container keyring.

It can be run from outside of the keyring like so:

./test-cont-grant <key> [<container-keyring>]

If the keyring isn't given, it will look for one called "_container"
in the session keyring where test-container is expected to have placed
it.

With kAFS, it can be used like follows:

kinit dhowells@REDHAT.COM
kafs-aklog redhat.com

which would log into kerberos and then get a key for accessing an AFS
cell called "redhat.com". This can be seen in the session keyring by
calling "keyctl show":

120378984 --alswrv 0 0 keyring: _ses
474754113 ---lswrv 0 65534 \_ keyring: _uid.0
64049961 --alswrv 0 0 \_ rxrpc: afs@redhat.com
78543393 --alswrv 0 0 \_ keyring: upcall
661655334 --alswrv 0 0 \_ keyring: _container
639103010 --alswrv 0 0 \_ user: foobar

Then doing:

./test-cont-grant 64049961

will result in:

120378984 --alswrv 0 0 keyring: _ses
474754113 ---lswrv 0 65534 \_ keyring: _uid.0
64049961 --alswrv 0 0 \_ rxrpc: afs@procyon.org.uk
78543393 --alswrv 0 0 \_ keyring: upcall
661655334 --alswrv 0 0 \_ keyring: _container
639103010 --alswrv 0 0 \_ user: foobar
64049961 --alswrv 0 0 \_ rxrpc: afs@procyon.org.uk

Inside the container, the cell could be mounted:

mount -t afs "%redhat.com:root.cell" /mnt

and then operations in /mnt will be done using the token that has been
made available. However, this can be overridden locally inside the
container by doing kinit and kafs-aklog there with a different user.

More to the point, the container manager could mount the container's
rootfs, say, over authenticated AFS and then attach the token to the
container and mount the rootfs into the container and the container's
inhabitant need not have any means to gain a kerberos login.

[?] I do wonder if the possibility to use container key searches for
direct mounts should be controlled by a mount option, say:

fsconfig(fsfd, FSCONFIG_SET_CONTAINER, NULL, NULL, cfd);

where you have to have the container handle available.

[!] Note that test-cont-grant picks the container by name and does not
require the container handle when setting the key ACL - but the
name must come from the set of children of the current container.

The patches can be found here also:

http://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/log/?h=container

Note that this is dependent on the mount-api-viro, fsinfo, notifications
and keys-namespace branches.

David
---
David Howells (27):
containers: Rename linux/container.h to linux/container_dev.h
containers: Implement containers as kernel objects
containers: Provide /proc/containers
containers: Allow a process to be forked into a container
containers: Open a socket inside a container
containers, vfs: Allow syscall dirfd arguments to take a container fd
containers: Make fsopen() able to create a superblock in a container
containers, vfs: Honour CONTAINER_NEW_EMPTY_FS_NS
vfs: Allow mounting to other namespaces
containers: Provide fs_context op for container setting
containers: Sample program for driving container objects
containers: Allow a daemon to intercept request_key upcalls in a container
keys: Provide a keyctl to query a request_key authentication key
keys: Break bits out of key_unlink()
keys: Make __key_link_begin() handle lockdep nesting
keys: Grant Link permission to possessers of request_key auth keys
keys: Add a keyctl to move a key between keyrings
keys: Find the least-recently used unseen key in a keyring.
containers: Sample: request_key upcall handling
container, keys: Add a container keyring
keys: Fix request_key() lack of Link perm check on found key
KEYS: Replace uid/gid/perm permissions checking with an ACL
KEYS: Provide KEYCTL_GRANT_PERMISSION
keys: Allow a container to be specified as a subject in a key's ACL
keys: Provide a way to ask for the container keyring
keys: Allow containers to be included in key ACLs by name
containers: Sample to grant access to a key in a container

arch/x86/entry/syscalls/syscall_32.tbl | 3
arch/x86/entry/syscalls/syscall_64.tbl | 3
arch/x86/ia32/sys_ia32.c | 2
certs/blacklist.c | 7
certs/system_keyring.c | 12
drivers/acpi/container.c | 2
drivers/base/container.c | 2
drivers/md/dm-crypt.c | 2
drivers/nvdimm/security.c | 2
fs/afs/security.c | 2
fs/afs/super.c | 18 +
fs/cifs/cifs_spnego.c | 25 +
fs/cifs/cifsacl.c | 28 +
fs/cifs/connect.c | 4
fs/crypto/keyinfo.c | 2
fs/ecryptfs/ecryptfs_kernel.h | 2
fs/ecryptfs/keystore.c | 2
fs/fs_context.c | 39 +
fs/fscache/object-list.c | 2
fs/fsopen.c | 54 ++
fs/namei.c | 45 +-
fs/namespace.c | 129 ++++-
fs/nfs/nfs4idmap.c | 29 +
fs/proc/root.c | 20 +
fs/ubifs/auth.c | 2
include/linux/container.h | 100 +++-
include/linux/container_dev.h | 25 +
include/linux/cred.h | 3
include/linux/fs_context.h | 5
include/linux/init_task.h | 1
include/linux/key-type.h | 2
include/linux/key.h | 122 +++--
include/linux/lsm_hooks.h | 20 +
include/linux/nsproxy.h | 7
include/linux/pid.h | 5
include/linux/proc_ns.h | 6
include/linux/sched.h | 3
include/linux/sched/task.h | 3
include/linux/security.h | 15 +
include/linux/socket.h | 3
include/linux/syscalls.h | 6
include/uapi/linux/container.h | 28 +
include/uapi/linux/keyctl.h | 85 +++
include/uapi/linux/mount.h | 4
init/Kconfig | 7
init/init_task.c | 3
ipc/mqueue.c | 10
kernel/Makefile | 2
kernel/container.c | 532 ++++++++++++++++++++
kernel/cred.c | 45 ++
kernel/exit.c | 1
kernel/fork.c | 111 ++++
kernel/namespaces.h | 15 +
kernel/nsproxy.c | 32 +
kernel/pid.c | 4
kernel/sys_ni.c | 5
lib/digsig.c | 2
net/ceph/ceph_common.c | 2
net/compat.c | 2
net/dns_resolver/dns_key.c | 12
net/dns_resolver/dns_query.c | 15 -
net/rxrpc/key.c | 16 -
net/socket.c | 34 +
samples/vfs/Makefile | 12
samples/vfs/test-cont-grant.c | 84 +++
samples/vfs/test-container.c | 382 ++++++++++++++
samples/vfs/test-upcall.c | 243 +++++++++
security/integrity/digsig.c | 31 -
security/integrity/digsig_asymmetric.c | 2
security/integrity/evm/evm_crypto.c | 2
security/integrity/ima/ima_mok.c | 13
security/integrity/integrity.h | 4
.../integrity/platform_certs/platform_keyring.c | 13
security/keys/Makefile | 2
security/keys/compat.c | 20 +
security/keys/container.c | 419 ++++++++++++++++
security/keys/encrypted-keys/encrypted.c | 2
security/keys/encrypted-keys/masterkey_trusted.c | 2
security/keys/gc.c | 2
security/keys/internal.h | 34 +
security/keys/key.c | 35 -
security/keys/keyctl.c | 176 +++++--
security/keys/keyring.c | 198 ++++++-
security/keys/permission.c | 446 +++++++++++++++--
security/keys/persistent.c | 27 +
security/keys/proc.c | 17 -
security/keys/process_keys.c | 102 +++-
security/keys/request_key.c | 70 ++-
security/keys/request_key_auth.c | 21 +
security/security.c | 12
security/selinux/hooks.c | 16 +
security/smack/smack_lsm.c | 3
92 files changed, 3696 insertions(+), 425 deletions(-)
create mode 100644 include/linux/container_dev.h
create mode 100644 include/uapi/linux/container.h
create mode 100644 kernel/container.c
create mode 100644 kernel/namespaces.h
create mode 100644 samples/vfs/test-cont-grant.c
create mode 100644 samples/vfs/test-container.c
create mode 100644 samples/vfs/test-upcall.c
create mode 100644 security/keys/container.c