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Rik van Riel c94203f462 livepatch: fix race between fork and KLP transition 
commit 747f7a2901 upstream.

The KLP transition code depends on the TIF_PATCH_PENDING and
the task->patch_state to stay in sync. On a normal (forward)
transition, TIF_PATCH_PENDING will be set on every task in
the system, while on a reverse transition (after a failed
forward one) first TIF_PATCH_PENDING will be cleared from
every task, followed by it being set on tasks that need to
be transitioned back to the original code.

However, the fork code copies over the TIF_PATCH_PENDING flag
from the parent to the child early on, in dup_task_struct and
setup_thread_stack. Much later, klp_copy_process will set
child->patch_state to match that of the parent.

However, the parent's patch_state may have been changed by KLP loading
or unloading since it was initially copied over into the child.

This results in the KLP code occasionally hitting this warning in
klp_complete_transition:

        for_each_process_thread(g, task) {
                WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
                task->patch_state = KLP_UNDEFINED;
        }

Set, or clear, the TIF_PATCH_PENDING flag in the child task
depending on whether or not it is needed at the time
klp_copy_process is called, at a point in copy_process where the
tasklist_lock is held exclusively, preventing races with the KLP
code.

The KLP code does have a few places where the state is changed
without the tasklist_lock held, but those should not cause
problems because klp_update_patch_state(current) cannot be
called while the current task is in the middle of fork,
klp_check_and_switch_task() which is called under the pi_lock,
which prevents rescheduling, and manipulation of the patch
state of idle tasks, which do not fork.

This should prevent this warning from triggering again in the
future, and close the race for both normal and reverse transitions.

Signed-off-by: Rik van Riel <riel@surriel.com>
Reported-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Fixes: d83a7cb375 ("livepatch: change to a per-task consistency model")
Cc: stable@kernel.org
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220808150019.03d6a67b@imladris.surriel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2022-10-26 13:16:57 +02:00
arch UM: cpuinfo: Fix a warning for CONFIG_CPUMASK_OFFSTACK 2022-10-26 13:16:56 +02:00
block block-map: add __GFP_ZERO flag for alloc_page in function bio_copy_kern 2022-06-06 08:20:57 +02:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-25 11:46:44 +02:00
crypto crypto: drbg - make reseeding from get_random_bytes() synchronous 2022-06-25 11:46:41 +02:00
Documentation ARM: dts: fix Moxa SDIO 'compatible', remove 'sdhci' misnomer 2022-10-26 13:16:52 +02:00
drivers fbdev: smscufx: Fix use-after-free in ufx_ops_open() 2022-10-26 13:16:56 +02:00
firmware Fix built-in early-load Intel microcode alignment 2020-01-23 08:20:30 +01:00
fs ext4: place buffer head allocation before handle start 2022-10-26 13:16:57 +02:00
include scsi: stex: Properly zero out the passthrough command structure 2022-10-26 13:16:54 +02:00
init random: handle latent entropy and command line from random_init() 2022-06-25 11:46:40 +02:00
ipc ipc: WARN if trying to remove ipc object which is absent 2021-12-08 08:46:53 +01:00
kernel livepatch: fix race between fork and KLP transition 2022-10-26 13:16:57 +02:00
lib ratelimit: Fix data-races in ___ratelimit(). 2022-09-05 10:25:04 +02:00
mm mm/migrate_device.c: flush TLB while holding PTL 2022-10-26 13:16:50 +02:00
net netfilter: nf_queue: fix socket leak 2022-10-26 13:16:53 +02:00
samples samples/kretprobes: Fix return value if register_kretprobe() failed 2021-11-26 11:40:31 +01:00
scripts Makefile.extrawarn: Move -Wcast-function-type-strict to W=1 2022-10-26 13:16:51 +02:00
security apparmor: fix reference count leak in aa_pivotroot() 2022-08-25 11:11:32 +02:00
sound ALSA: usb-audio: Fix NULL dererence at error path 2022-10-26 13:16:55 +02:00
tools selftests: Fix the if conditions of in test_extra_filter() 2022-10-26 13:16:51 +02:00
usr initramfs: restore default compression behavior 2020-04-13 10:34:19 +02:00
virt KVM: Add infrastructure and macro to mark VM as bugged 2022-08-25 11:11:29 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: rpm-pkg: keep spec file until make mrproper 2018-02-13 10:19:46 +01:00
.mailmap .mailmap: Add Maciej W. Rozycki's Imagination e-mail address 2017-11-10 12:16:15 -08:00
COPYING
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS MAINTAINERS: co-maintain random.c 2022-06-25 11:46:29 +02:00
Makefile Linux 4.14.295 2022-09-28 10:56:52 +02:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.