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Linus Torvalds 591beb0e3a io_uring-bpf-restrictions.4-20260206
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Merge tag 'io_uring-bpf-restrictions.4-20260206' of git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux

Pull io_uring bpf filters from Jens Axboe:
 "This adds support for both cBPF filters for io_uring, as well as task
  inherited restrictions and filters.

  seccomp and io_uring don't play along nicely, as most of the
  interesting data to filter on resides somewhat out-of-band, in the
  submission queue ring.

  As a result, things like containers and systemd that apply seccomp
  filters, can't filter io_uring operations.

  That leaves them with just one choice if filtering is critical -
  filter the actual io_uring_setup(2) system call to simply disallow
  io_uring. That's rather unfortunate, and has limited us because of it.

  io_uring already has some filtering support. It requires the ring to
  be setup in a disabled state, and then a filter set can be applied.
  This filter set is completely bi-modal - an opcode is either enabled
  or it's not. Once a filter set is registered, the ring can be enabled.
  This is very restrictive, and it's not useful at all to systemd or
  containers which really want both broader and more specific control.

  This first adds support for cBPF filters for opcodes, which enables
  tighter control over what exactly a specific opcode may do. As
  examples, specific support is added for IORING_OP_OPENAT/OPENAT2,
  allowing filtering on resolve flags. And another example is added for
  IORING_OP_SOCKET, allowing filtering on domain/type/protocol. These
  are both common use cases. cBPF was chosen rather than eBPF, because
  the latter is often restricted in containers as well.

  These filters are run post the init phase of the request, which allows
  filters to even dip into data that is being passed in struct in user
  memory, as the init side of requests make that data stable by bringing
  it into the kernel. This allows filtering without needing to copy this
  data twice, or have filters etc know about the exact layout of the
  user data. The filters get the already copied and sanitized data
  passed.

  On top of that support is added for per-task filters, meaning that any
  ring created with a task that has a per-task filter will get those
  filters applied when it's created. These filters are inherited across
  fork as well. Once a filter has been registered, any further added
  filters may only further restrict what operations are permitted.

  Filters cannot change the return value of an operation, they can only
  permit or deny it based on the contents"

* tag 'io_uring-bpf-restrictions.4-20260206' of git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux:
  io_uring: allow registration of per-task restrictions
  io_uring: add task fork hook
  io_uring/bpf_filter: add ref counts to struct io_bpf_filter
  io_uring/bpf_filter: cache lookup table in ctx->bpf_filters
  io_uring/bpf_filter: allow filtering on contents of struct open_how
  io_uring/net: allow filtering on IORING_OP_SOCKET data
  io_uring: add support for BPF filtering for opcode restrictions
History 2026-02-09 17:31:17 -08:00
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Linux kernel
============

The Linux kernel is the core of any Linux operating system. It manages hardware,
system resources, and provides the fundamental services for all other software.

Quick Start
-----------

* Report a bug: See Documentation/admin-guide/reporting-issues.rst
* Get the latest kernel: https://kernel.org
* Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst
* Join the community: https://lore.kernel.org/

Essential Documentation
-----------------------

All users should be familiar with:

* Building requirements: Documentation/process/changes.rst
* Code of Conduct: Documentation/process/code-of-conduct.rst
* License: See COPYING

Documentation can be built with make htmldocs or viewed online at:
https://www.kernel.org/doc/html/latest/


Who Are You?
============

Find your role below:

* New Kernel Developer - Getting started with kernel development
* Academic Researcher - Studying kernel internals and architecture
* Security Expert - Hardening and vulnerability analysis
* Backport/Maintenance Engineer - Maintaining stable kernels
* System Administrator - Configuring and troubleshooting
* Maintainer - Leading subsystems and reviewing patches
* Hardware Vendor - Writing drivers for new hardware
* Distribution Maintainer - Packaging kernels for distros


For Specific Users
==================

New Kernel Developer
--------------------

Welcome! Start your kernel development journey here:

* Getting Started: Documentation/process/development-process.rst
* Your First Patch: Documentation/process/submitting-patches.rst
* Coding Style: Documentation/process/coding-style.rst
* Build System: Documentation/kbuild/index.rst
* Development Tools: Documentation/dev-tools/index.rst
* Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst
* Core APIs: Documentation/core-api/index.rst

Academic Researcher
-------------------

Explore the kernel's architecture and internals:

* Researcher Guidelines: Documentation/process/researcher-guidelines.rst
* Memory Management: Documentation/mm/index.rst
* Scheduler: Documentation/scheduler/index.rst
* Networking Stack: Documentation/networking/index.rst
* Filesystems: Documentation/filesystems/index.rst
* RCU (Read-Copy Update): Documentation/RCU/index.rst
* Locking Primitives: Documentation/locking/index.rst
* Power Management: Documentation/power/index.rst

Security Expert
---------------

Security documentation and hardening guides:

* Security Documentation: Documentation/security/index.rst
* LSM Development: Documentation/security/lsm-development.rst
* Self Protection: Documentation/security/self-protection.rst
* Reporting Vulnerabilities: Documentation/process/security-bugs.rst
* CVE Procedures: Documentation/process/cve.rst
* Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst
* Security Features: Documentation/userspace-api/seccomp_filter.rst

Backport/Maintenance Engineer
-----------------------------

Maintain and stabilize kernel versions:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* Backporting Guide: Documentation/process/backporting.rst
* Applying Patches: Documentation/process/applying-patches.rst
* Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git for Maintainers: Documentation/maintainer/configure-git.rst

System Administrator
--------------------

Configure, tune, and troubleshoot Linux systems:

* Admin Guide: Documentation/admin-guide/index.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst
* Tracing/Debugging: Documentation/trace/index.rst
* Performance Security: Documentation/admin-guide/perf-security.rst
* Hardware Monitoring: Documentation/hwmon/index.rst

Maintainer
----------

Lead kernel subsystems and manage contributions:

* Maintainer Handbook: Documentation/maintainer/index.rst
* Pull Requests: Documentation/maintainer/pull-requests.rst
* Managing Patches: Documentation/maintainer/modifying-patches.rst
* Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst
* Development Process: Documentation/process/maintainer-handbooks.rst
* Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git Configuration: Documentation/maintainer/configure-git.rst

Hardware Vendor
---------------

Write drivers and support new hardware:

* Driver API Guide: Documentation/driver-api/index.rst
* Driver Model: Documentation/driver-api/driver-model/driver.rst
* Device Drivers: Documentation/driver-api/infrastructure.rst
* Bus Types: Documentation/driver-api/driver-model/bus.rst
* Device Tree Bindings: Documentation/devicetree/bindings/
* Power Management: Documentation/driver-api/pm/index.rst
* DMA API: Documentation/core-api/dma-api.rst

Distribution Maintainer
-----------------------

Package and distribute the kernel:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* ABI Documentation: Documentation/ABI/README
* Kernel Configuration: Documentation/kbuild/kconfig.rst
* Module Signing: Documentation/admin-guide/module-signing.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst



Communication and Support
=========================

* Mailing Lists: https://lore.kernel.org/
* IRC: #kernelnewbies on irc.oftc.net
* Bugzilla: https://bugzilla.kernel.org/
* MAINTAINERS file: Lists subsystem maintainers and mailing lists
* Email Clients: Documentation/process/email-clients.rst