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Merge tag 'notifications-20200601' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs
Pull notification queue from David Howells:
"This adds a general notification queue concept and adds an event
source for keys/keyrings, such as linking and unlinking keys and
changing their attributes.
Thanks to Debarshi Ray, we do have a pull request to use this to fix a
problem with gnome-online-accounts - as mentioned last time:
https://gitlab.gnome.org/GNOME/gnome-online-accounts/merge_requests/47
Without this, g-o-a has to constantly poll a keyring-based kerberos
cache to find out if kinit has changed anything.
[ There are other notification pending: mount/sb fsinfo notifications
for libmount that Karel Zak and Ian Kent have been working on, and
Christian Brauner would like to use them in lxc, but let's see how
this one works first ]
LSM hooks are included:
- A set of hooks are provided that allow an LSM to rule on whether or
not a watch may be set. Each of these hooks takes a different
"watched object" parameter, so they're not really shareable. The
LSM should use current's credentials. [Wanted by SELinux & Smack]
- A hook is provided to allow an LSM to rule on whether or not a
particular message may be posted to a particular queue. This is
given the credentials from the event generator (which may be the
system) and the watch setter. [Wanted by Smack]
I've provided SELinux and Smack with implementations of some of these
hooks.
WHY
===
Key/keyring notifications are desirable because if you have your
kerberos tickets in a file/directory, your Gnome desktop will monitor
that using something like fanotify and tell you if your credentials
cache changes.
However, we also have the ability to cache your kerberos tickets in
the session, user or persistent keyring so that it isn't left around
on disk across a reboot or logout. Keyrings, however, cannot currently
be monitored asynchronously, so the desktop has to poll for it - not
so good on a laptop. This facility will allow the desktop to avoid the
need to poll.
DESIGN DECISIONS
================
- The notification queue is built on top of a standard pipe. Messages
are effectively spliced in. The pipe is opened with a special flag:
pipe2(fds, O_NOTIFICATION_PIPE);
The special flag has the same value as O_EXCL (which doesn't seem
like it will ever be applicable in this context)[?]. It is given up
front to make it a lot easier to prohibit splice&co from accessing
the pipe.
[?] Should this be done some other way? I'd rather not use up a new
O_* flag if I can avoid it - should I add a pipe3() system call
instead?
The pipe is then configured::
ioctl(fds[1], IOC_WATCH_QUEUE_SET_SIZE, queue_depth);
ioctl(fds[1], IOC_WATCH_QUEUE_SET_FILTER, &filter);
Messages are then read out of the pipe using read().
- It should be possible to allow write() to insert data into the
notification pipes too, but this is currently disabled as the
kernel has to be able to insert messages into the pipe *without*
holding pipe->mutex and the code to make this work needs careful
auditing.
- sendfile(), splice() and vmsplice() are disabled on notification
pipes because of the pipe->mutex issue and also because they
sometimes want to revert what they just did - but one or more
notification messages might've been interleaved in the ring.
- The kernel inserts messages with the wait queue spinlock held. This
means that pipe_read() and pipe_write() have to take the spinlock
to update the queue pointers.
- Records in the buffer are binary, typed and have a length so that
they can be of varying size.
This allows multiple heterogeneous sources to share a common
buffer; there are 16 million types available, of which I've used
just a few, so there is scope for others to be used. Tags may be
specified when a watchpoint is created to help distinguish the
sources.
- Records are filterable as types have up to 256 subtypes that can be
individually filtered. Other filtration is also available.
- Notification pipes don't interfere with each other; each may be
bound to a different set of watches. Any particular notification
will be copied to all the queues that are currently watching for it
- and only those that are watching for it.
- When recording a notification, the kernel will not sleep, but will
rather mark a queue as having lost a message if there's
insufficient space. read() will fabricate a loss notification
message at an appropriate point later.
- The notification pipe is created and then watchpoints are attached
to it, using one of:
keyctl_watch_key(KEY_SPEC_SESSION_KEYRING, fds[1], 0x01);
watch_mount(AT_FDCWD, "/", 0, fd, 0x02);
watch_sb(AT_FDCWD, "/mnt", 0, fd, 0x03);
where in both cases, fd indicates the queue and the number after is
a tag between 0 and 255.
- Watches are removed if either the notification pipe is destroyed or
the watched object is destroyed. In the latter case, a message will
be generated indicating the enforced watch removal.
Things I want to avoid:
- Introducing features that make the core VFS dependent on the
network stack or networking namespaces (ie. usage of netlink).
- Dumping all this stuff into dmesg and having a daemon that sits
there parsing the output and distributing it as this then puts the
responsibility for security into userspace and makes handling
namespaces tricky. Further, dmesg might not exist or might be
inaccessible inside a container.
- Letting users see events they shouldn't be able to see.
TESTING AND MANPAGES
====================
- The keyutils tree has a pipe-watch branch that has keyctl commands
for making use of notifications. Proposed manual pages can also be
found on this branch, though a couple of them really need to go to
the main manpages repository instead.
If the kernel supports the watching of keys, then running "make
test" on that branch will cause the testing infrastructure to spawn
a monitoring process on the side that monitors a notifications pipe
for all the key/keyring changes induced by the tests and they'll
all be checked off to make sure they happened.
https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/keyutils.git/log/?h=pipe-watch
- A test program is provided (samples/watch_queue/watch_test) that
can be used to monitor for keyrings, mount and superblock events.
Information on the notifications is simply logged to stdout"
* tag 'notifications-20200601' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
smack: Implement the watch_key and post_notification hooks
selinux: Implement the watch_key security hook
keys: Make the KEY_NEED_* perms an enum rather than a mask
pipe: Add notification lossage handling
pipe: Allow buffers to be marked read-whole-or-error for notifications
Add sample notification program
watch_queue: Add a key/keyring notification facility
security: Add hooks to rule on setting a watch
pipe: Add general notification queue support
pipe: Add O_NOTIFICATION_PIPE
security: Add a hook for the point of notification insertion
uapi: General notification queue definitions
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# SPDX-License-Identifier: GPL-2.0-only
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#
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# Key management configuration
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#
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config KEYS
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bool "Enable access key retention support"
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select ASSOCIATIVE_ARRAY
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help
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This option provides support for retaining authentication tokens and
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access keys in the kernel.
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It also includes provision of methods by which such keys might be
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associated with a process so that network filesystems, encryption
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support and the like can find them.
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Furthermore, a special type of key is available that acts as keyring:
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a searchable sequence of keys. Each process is equipped with access
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to five standard keyrings: UID-specific, GID-specific, session,
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process and thread.
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If you are unsure as to whether this is required, answer N.
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config KEYS_REQUEST_CACHE
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bool "Enable temporary caching of the last request_key() result"
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depends on KEYS
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help
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This option causes the result of the last successful request_key()
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call that didn't upcall to the kernel to be cached temporarily in the
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task_struct. The cache is cleared by exit and just prior to the
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resumption of userspace.
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This allows the key used for multiple step processes where each step
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wants to request a key that is likely the same as the one requested
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by the last step to save on the searching.
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An example of such a process is a pathwalk through a network
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filesystem in which each method needs to request an authentication
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key. Pathwalk will call multiple methods for each dentry traversed
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(permission, d_revalidate, lookup, getxattr, getacl, ...).
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config PERSISTENT_KEYRINGS
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bool "Enable register of persistent per-UID keyrings"
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depends on KEYS
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help
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This option provides a register of persistent per-UID keyrings,
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primarily aimed at Kerberos key storage. The keyrings are persistent
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in the sense that they stay around after all processes of that UID
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have exited, not that they survive the machine being rebooted.
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A particular keyring may be accessed by either the user whose keyring
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it is or by a process with administrative privileges. The active
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LSMs gets to rule on which admin-level processes get to access the
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cache.
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Keyrings are created and added into the register upon demand and get
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removed if they expire (a default timeout is set upon creation).
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config BIG_KEYS
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bool "Large payload keys"
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depends on KEYS
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depends on TMPFS
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depends on CRYPTO_LIB_CHACHA20POLY1305 = y
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help
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This option provides support for holding large keys within the kernel
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(for example Kerberos ticket caches). The data may be stored out to
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swapspace by tmpfs.
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If you are unsure as to whether this is required, answer N.
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config TRUSTED_KEYS
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tristate "TRUSTED KEYS"
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depends on KEYS && TCG_TPM
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select CRYPTO
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select CRYPTO_HMAC
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select CRYPTO_SHA1
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select CRYPTO_HASH_INFO
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help
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This option provides support for creating, sealing, and unsealing
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keys in the kernel. Trusted keys are random number symmetric keys,
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generated and RSA-sealed by the TPM. The TPM only unseals the keys,
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if the boot PCRs and other criteria match. Userspace will only ever
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see encrypted blobs.
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If you are unsure as to whether this is required, answer N.
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config ENCRYPTED_KEYS
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tristate "ENCRYPTED KEYS"
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depends on KEYS
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select CRYPTO
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select CRYPTO_HMAC
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select CRYPTO_AES
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select CRYPTO_CBC
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select CRYPTO_SHA256
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select CRYPTO_RNG
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help
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This option provides support for create/encrypting/decrypting keys
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in the kernel. Encrypted keys are kernel generated random numbers,
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which are encrypted/decrypted with a 'master' symmetric key. The
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'master' key can be either a trusted-key or user-key type.
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Userspace only ever sees/stores encrypted blobs.
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If you are unsure as to whether this is required, answer N.
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config KEY_DH_OPERATIONS
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bool "Diffie-Hellman operations on retained keys"
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depends on KEYS
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select CRYPTO
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select CRYPTO_HASH
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select CRYPTO_DH
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help
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This option provides support for calculating Diffie-Hellman
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public keys and shared secrets using values stored as keys
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in the kernel.
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If you are unsure as to whether this is required, answer N.
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config KEY_NOTIFICATIONS
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bool "Provide key/keyring change notifications"
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depends on KEYS && WATCH_QUEUE
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help
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This option provides support for getting change notifications on keys
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and keyrings on which the caller has View permission. This makes use
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of the /dev/watch_queue misc device to handle the notification
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buffer and provides KEYCTL_WATCH_KEY to enable/disable watches.
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