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### Background Various admin operations will be invoked by some userspace task, but the work will be done on a separate kernel thread at a later time. Snapshots are an example, which are triggered through zfs_ioc_snapshot() -> dsl_dataset_snapshot(), but the actual work is from a task dispatched to dp_sync_taskq. Many such tasks end up in dsl_enforce_ds_ss_limits(), where various limits and permissions are enforced. Among other things, it is necessary to ensure that the invoking task (that is, the user) has permission to do things. We can't simply check if the running task has permission; it is a privileged kernel thread, which can do anything. However, in the general case it's not safe to simply query the task for its permissions at the check time, as the task may not exist any more, or its permissions may have changed since it was first invoked. So instead, we capture the permissions by saving CRED() in the user task, and then using it for the check through the secpolicy_* functions. ### Current implementation The current code calls CRED() to get the credential, which gets a pointer to the cred_t inside the current task and passes it to the worker task. However, it doesn't take a reference to the cred_t, and so expects that it won't change, and that the task continues to exist. In practice that is always the case, because we don't let the calling task return from the kernel until the work is done. For Linux, we also take a reference to the current task, because the Linux credential APIs for the most part do not check an arbitrary credential, but rather, query what a task can do. See secpolicy_zfs_proc(). Again, we don't take a reference on the task, just a pointer to it. ### Changes We change to calling crhold() on the task credential, and crfree() when we're done with it. This ensures it stays alive and unchanged for the duration of the call. On the Linux side, we change the main policy checking function priv_policy_ns() to use override_creds()/revert_creds() if necessary to make the provided credential active in the current task, allowing the standard task-permission APIs to do the needed check. Since the task pointer is no longer required, this lets us entirely remove secpolicy_zfs_proc() and the need to carry a task pointer around as well. Sponsored-by: https://despairlabs.com/sponsor/ Signed-off-by: Rob Norris <robn@despairlabs.com> Reviewed-by: Pavel Snajdr <snajpa@snajpa.net> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Reviewed-by: Kyle Evans <kevans@FreeBSD.org> Reviewed-by: Tony Hutter <hutter2@llnl.gov> |
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OpenZFS is an advanced file system and volume manager which was originally developed for Solaris and is now maintained by the OpenZFS community. This repository contains the code for running OpenZFS on Linux and FreeBSD.
Official Resources
- Documentation - for using and developing this repo
- ZoL Site - Linux release info & links
- Mailing lists
- OpenZFS site - for conference videos and info on other platforms (illumos, OSX, Windows, etc)
Installation
Full documentation for installing OpenZFS on your favorite operating system can be found at the Getting Started Page.
Contribute & Develop
We have a separate document with contribution guidelines.
We have a Code of Conduct.
Release
OpenZFS is released under a CDDL license.
For more details see the NOTICE, LICENSE and COPYRIGHT files; UCRL-CODE-235197
Supported Kernels
- The
METAfile contains the officially recognized supported Linux kernel versions. - Supported FreeBSD versions are any supported branches and releases starting from 13.0-RELEASE.