Debian: CVE-2025-21948: linux, linux-6.1 -- security update

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

HID: appleir: Fix potential NULL dereference at raw event handle

Syzkaller reports a NULL pointer dereference issue in input_event().

BUG: KASAN: null-ptr-deref in instrument_atomic_read include/linux/instrumented.h:68 [inline]
BUG: KASAN: null-ptr-deref in _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
BUG: KASAN: null-ptr-deref in is_event_supported drivers/input/input.c:67 [inline]
BUG: KASAN: null-ptr-deref in input_event+0x42/0xa0 drivers/input/input.c:395
Read of size 8 at addr 0000000000000028 by task syz-executor199/2949

CPU: 0 UID: 0 PID: 2949 Comm: syz-executor199 Not tainted 6.13.0-rc4-syzkaller-00076-gf097a36ef88d #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
kasan_report+0xd9/0x110 mm/kasan/report.c:602
check_region_inline mm/kasan/generic.c:183 [inline]
kasan_check_range+0xef/0x1a0 mm/kasan/generic.c:189
instrument_atomic_read include/linux/instrumented.h:68 [inline]
_test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
is_event_supported drivers/input/input.c:67 [inline]
input_event+0x42/0xa0 drivers/input/input.c:395
input_report_key include/linux/input.h:439 [inline]
key_down drivers/hid/hid-appleir.c:159 [inline]
appleir_raw_event+0x3e5/0x5e0 drivers/hid/hid-appleir.c:232
__hid_input_report.constprop.0+0x312/0x440 drivers/hid/hid-core.c:2111
hid_ctrl+0x49f/0x550 drivers/hid/usbhid/hid-core.c:484
__usb_hcd_giveback_urb+0x389/0x6e0 drivers/usb/core/hcd.c:1650
usb_hcd_giveback_urb+0x396/0x450 drivers/usb/core/hcd.c:1734
dummy_timer+0x17f7/0x3960 drivers/usb/gadget/udc/dummy_hcd.c:1993
__run_hrtimer kernel/time/hrtimer.c:1739 [inline]
__hrtimer_run_queues+0x20a/0xae0 kernel/time/hrtimer.c:1803
hrtimer_run_softirq+0x17d/0x350 kernel/time/hrtimer.c:1820
handle_softirqs+0x206/0x8d0 kernel/softirq.c:561
__do_softirq kernel/softirq.c:595 [inline]
invoke_softirq kernel/softirq.c:435 [inline]
__irq_exit_rcu+0xfa/0x160 kernel/softirq.c:662
irq_exit_rcu+0x9/0x30 kernel/softirq.c:678
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1049 [inline]
sysvec_apic_timer_interrupt+0x90/0xb0 arch/x86/kernel/apic/apic.c:1049
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
__mod_timer+0x8f6/0xdc0 kernel/time/timer.c:1185
add_timer+0x62/0x90 kernel/time/timer.c:1295
schedule_timeout+0x11f/0x280 kernel/time/sleep_timeout.c:98
usbhid_wait_io+0x1c7/0x380 drivers/hid/usbhid/hid-core.c:645
usbhid_init_reports+0x19f/0x390 drivers/hid/usbhid/hid-core.c:784
hiddev_ioctl+0x1133/0x15b0 drivers/hid/usbhid/hiddev.c:794
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:906 [inline]
__se_sys_ioctl fs/ioctl.c:892 [inline]
__x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
</TASK>

This happens due to the malformed report items sent by the emulated device
which results in a report, that has no fields, being added to the report list.
Due to this appleir_input_configured() is never called, hidinput_connect()
fails which results in the HID_CLAIMED_INPUT flag is not being set. However,
it does not make appleir_probe() fail and lets the event callback to be
called without the associated input device.

Thus, add a check for the HID_CLAIMED_INPUT flag and leave the event hook
early if the driver didn't claim any input_dev for some reason. Moreover,
some other hid drivers accessing input_dev in their event callbacks do have
similar checks, too.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.