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Breno Leitao 859c199bb3
fs/select: reject negative timeval components in kern_select()
kern_select() normalises the user-supplied struct __kernel_old_timeval
with

	tv.tv_sec + (tv.tv_usec / USEC_PER_SEC)
	(tv.tv_usec % USEC_PER_SEC) * NSEC_PER_USEC

before calling poll_select_set_timeout() -> timespec64_valid().  Both
operands of the seconds sum are unbounded user-controlled signed long.
A crafted pair where tv_usec is a negative multiple of USEC_PER_SEC
drives the sum across the wrap boundary - e.g.

	{ .tv_sec = LONG_MIN, .tv_usec = -1000000 }

yields sec = LONG_MAX, nsec = 0, which passes timespec64_valid() and
then flows through timespec64_add_safe(), which saturates the absolute
deadline to TIME64_MAX (clamped further to KTIME_MAX downstream).
select(2) therefore blocks effectively forever instead of returning
-EINVAL as POSIX requires for a negative timeout.

Only the legacy __NR_select syscall takes this path.  pselect6, ppoll,
poll and epoll_pwait2 all hand the user's two fields directly to
poll_select_set_timeout(), which validates *before* doing any
arithmetic:

	/* fs/select.c:271 -- the validator */
	int poll_select_set_timeout(struct timespec64 *to, time64_t sec, long nsec)
	{
		struct timespec64 ts = {.tv_sec = sec, .tv_nsec = nsec};
		if (!timespec64_valid(&ts))
			return -EINVAL;
		...
	}

	/* include/linux/time64.h:97 -- timespec64_valid */
	if (ts->tv_sec < 0)                              return false;
	if ((unsigned long)ts->tv_nsec >= NSEC_PER_SEC)  return false;

	/* fs/select.c:744  do_pselect() (pselect6, pselect6_time32) */
	if (get_timespec64(&ts, tsp)) return -EFAULT;
	if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec)) return -EINVAL;

	/* fs/select.c:1097 ppoll */
	if (get_timespec64(&ts, tsp)) return -EFAULT;
	if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec)) return -EINVAL;

	/* fs/select.c:1065 poll -- timeout_msecs is int; >= 0 gates the math */
	if (timeout_msecs >= 0)
		poll_select_set_timeout(to, timeout_msecs / MSEC_PER_SEC,
		                        NSEC_PER_MSEC * (timeout_msecs % MSEC_PER_SEC));

	/* fs/eventpoll.c:2512 epoll_pwait2 */
	if (get_timespec64(&ts, timeout)) return -EFAULT;
	if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec)) return -EINVAL;

In every one of these the wrap-prone arithmetic from kern_select()
simply does not exist; the user fields reach timespec64_valid()
unmodified.  glibc routes the C-library select() through pselect6,
so the bug is reachable only via a direct syscall(__NR_select, ...).

The pre-validation negative check that used to live here was lost
when the syscall was switched to the poll_select_set_timeout() helper.
Restore it: reject tv_sec < 0 || tv_usec < 0 up front, mirroring what
glibc does in userspace.  do_compat_select() has the same arithmetic
pattern but is only reachable on 32-bit compat and from a different
syscall entry; left for a follow-up so this change stays minimal.

Reproducer (returns -1/EINVAL on a fixed kernel; blocks indefinitely
on an unfixed one):

	struct timeval tv = { .tv_sec = LONG_MIN, .tv_usec = -1000000 };
	fd_set r;
	int pfd[2];
	pipe(pfd);
	FD_ZERO(&r);
	FD_SET(pfd[0], &r);
	syscall(__NR_select, pfd[0] + 1, &r, NULL, NULL, &tv);

Fixes: 4d36a9e65d ("select: deal with math overflow from borderline valid userland data")
Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20260429-timeval-v1-1-4448e2588bbf@debian.org
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
2026-05-12 14:41:40 +02:00
Documentation hwmon fixes for v7.1-rc3 2026-05-09 08:32:50 -07:00
LICENSES LICENSES: Add modern form of the LGPL-2.1 tags to the usage guide section 2025-10-22 07:58:19 +02:00
arch powerpc fixes for 7.1 #2 2026-05-09 08:03:21 -07:00
block block: only read from sqe on initial invocation of blkdev_uring_cmd() 2026-05-05 01:37:12 -06:00
certs Clang build fixes for 7.1 2026-04-24 09:29:51 -07:00
crypto This push contains the following changes: 2026-05-02 12:31:43 -07:00
drivers - Fix a string leak in the versalnet driver 2026-05-10 12:21:57 -07:00
fs fs/select: reject negative timeval components in kern_select() 2026-05-12 14:41:40 +02:00
include bpf-fixes 2026-05-09 18:42:54 -07:00
init memblock: updates for 7.0-rc1 2026-04-18 11:29:14 -07:00
io_uring io_uring-7.1-20260508 2026-05-08 13:12:48 -07:00
ipc Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
kernel bpf-fixes 2026-05-09 18:42:54 -07:00
lib fbdev fixes & cleanups for 7.1-rc3: 2026-05-05 14:25:44 -07:00
mm slab fixes for 7.1-rc1 2026-05-03 08:19:57 -07:00
net rxrpc: Also unshare DATA/RESPONSE packets when paged frags are present 2026-05-10 08:15:57 -07:00
rust Rust fixes for v7.1 2026-05-09 11:24:02 -07:00
samples soc: drivers for 7.1 2026-04-16 20:34:34 -07:00
scripts First round of Kbuild fixes for 7.1 2026-04-25 17:04:15 -07:00
security selinux: shrink critical section in sel_write_load() 2026-05-05 16:02:28 -04:00
sound ASoC: Fixes for v7.1 2026-05-06 16:10:00 +02:00
tools bpf-fixes 2026-05-09 18:42:54 -07:00
usr kbuild: uapi: also test UAPI headers against C++ compilers 2026-03-25 13:24:42 +01:00
virt Arm: 2026-04-17 07:18:03 -07:00
.clang-format Devicetree updates for v7.0: 2026-02-11 18:27:08 -08:00
.clippy.toml rust: bump Clippy's MSRV and clean `incompatible_msrv` allows 2026-04-07 09:51:39 +02:00
.cocciconfig
.editorconfig editorconfig: add rst extension 2026-01-26 19:07:09 -08:00
.get_maintainer.ignore .get_maintainer.ignore: add Askar 2026-04-15 02:15:02 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: rust: provide an option to inline C helpers into Rust 2026-03-30 02:03:52 +02:00
.mailmap MAINTAINERS: Update mail for Peter Rosin 2026-05-04 21:02:58 +02:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -07:00
.rustfmt.toml rust: add `.rustfmt.toml` 2022-09-28 09:02:20 +02:00
COPYING
CREDITS Delete some obsolete networking code 2026-04-24 09:41:58 -07:00
Kbuild checksyscalls: move instance functionality into generic code 2026-04-05 09:21:32 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS Fixes for clk drivers: 2026-05-10 08:10:47 -07:00
Makefile Linux 7.1-rc3 2026-05-10 14:08:09 -07:00
README docs: add AI Coding Assistants documentation 2026-01-06 14:55:06 -07:00

README

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
* AI Coding Assistant - LLMs and AI-powered development tools


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

AI Coding Assistant
-------------------

CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and
follow the AI coding assistants documentation before contributing to the Linux
kernel:

* Documentation/process/coding-assistants.rst

This documentation contains essential requirements about licensing, attribution,
and the Developer Certificate of Origin that all AI tools must comply with.


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