Merge tag 'notifications-20200601' of...
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
Showing
This diff is collapsed.
This diff is collapsed.
include/linux/watch_queue.h
0 → 100644
kernel/watch_queue.c
0 → 100644
This diff is collapsed.
samples/watch_queue/Makefile
0 → 100644
Please register or sign in to comment