Ubuntu: (Multiple Advisories) (CVE-2025-21943): Linux kernel vulnerabilities

In the Linux kernel, the following vulnerability has been resolved:

gpio: aggregator: protect driver attr handlers against module unload

Both new_device_store and delete_device_store touch module global
resources (e.g. gpio_aggregator_lock). To prevent race conditions with
module unload, a reference needs to be held.

Add try_module_get() in these handlers.

For new_device_store, this eliminates what appears to be the most dangerous
scenario: if an id is allocated from gpio_aggregator_idr but
platform_device_register has not yet been called or completed, a concurrent
module unload could fail to unregister/delete the device, leaving behind a
dangling platform device/GPIO forwarder. This can result in various issues.
The following simple reproducer demonstrates these problems:

#!/bin/bash
while :; do
# note: whether 'gpiochip0 0' exists or not does not matter.
echo 'gpiochip0 0' > /sys/bus/platform/drivers/gpio-aggregator/new_device
done &
while :; do
modprobe gpio-aggregator
modprobe -r gpio-aggregator
done &
wait

Starting with the following warning, several kinds of warnings will appear
and the system may become unstable:

------------[ cut here ]------------
list_del corruption, ffff888103e2e980->next is LIST_POISON1 (dead000000000100)
WARNING: CPU: 1 PID: 1327 at lib/list_debug.c:56 __list_del_entry_valid_or_report+0xa3/0x120
[...]
RIP: 0010:__list_del_entry_valid_or_report+0xa3/0x120
[...]
Call Trace:
<TASK>
? __list_del_entry_valid_or_report+0xa3/0x120
? __warn.cold+0x93/0xf2
? __list_del_entry_valid_or_report+0xa3/0x120
? report_bug+0xe6/0x170
? __irq_work_queue_local+0x39/0xe0
? handle_bug+0x58/0x90
? exc_invalid_op+0x13/0x60
? asm_exc_invalid_op+0x16/0x20
? __list_del_entry_valid_or_report+0xa3/0x120
gpiod_remove_lookup_table+0x22/0x60
new_device_store+0x315/0x350 [gpio_aggregator]
kernfs_fop_write_iter+0x137/0x1f0
vfs_write+0x262/0x430
ksys_write+0x60/0xd0
do_syscall_64+0x6c/0x180
entry_SYSCALL_64_after_hwframe+0x76/0x7e
[...]
</TASK>
---[ end trace 0000000000000000 ]---