mirror_zfs/module
Rob Norris 4ee13684b9 cred: properly pass and test creds on other threads (#17273)
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.

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.

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>
2025-06-02 16:49:51 -07:00
..
avl Suppress Clang Static Analyzer false positive in the AVL tree code. 2023-03-08 13:51:21 -08:00
icp icp: Use explicit_memset() exclusively in gcm_clear_ctx() 2025-05-27 14:41:45 -07:00
lua lua: add flex array field to TString type 2024-11-05 15:43:52 -08:00
nvpair xdr: header cleanup 2024-04-29 13:50:05 -07:00
os cred: properly pass and test creds on other threads (#17273) 2025-06-02 16:49:51 -07:00
unicode Illumos #15286: do_composition() needs sign awareness 2023-01-05 11:16:21 -08:00
zcommon GCC 15: Fix unterminated-string-initialization (#17244) 2025-05-27 15:03:11 -07:00
zfs cred: properly pass and test creds on other threads (#17273) 2025-06-02 16:49:51 -07:00
zstd Resolve WS-2021-0184 vulnerability in zstd 2023-02-02 15:12:51 -08:00
.gitignore FreeBSD: Ignore symlink to i386 includes 2022-08-02 16:34:23 -07:00
Kbuild.in Linux build: always use objtool 2025-05-30 15:08:01 -07:00
Makefile.bsd zfs_znode: lift common code to a single shared file 2024-11-15 10:15:01 -08:00
Makefile.in Support for cross-compiling kernel modules 2025-05-27 14:54:34 -07:00