[syzbot] [hams?] KMSAN: uninit-value in sixpack_receive_buf (4)

[syzbot <syzbot+ecdb8c9878a81eb21e54@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    fd95357fd8c6 Merge tag 'sched_ext-for-6.18-rc6-fixes-2' of..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14b20e92580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=61a9bf3cc5d17a01
dashboard link: https://syzkaller.appspot.com/bug?extid=ecdb8c9878a81eb21e54
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/68372e629a75/disk-fd95357f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d18e790887c9/vmlinux-fd95357f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4eb563ad2c24/bzImage-fd95357f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ecdb8c9878a81eb21e54@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in sixpack_decode drivers/net/hamradio/6pack.c:891 [inline]
BUG: KMSAN: uninit-value in sixpack_receive_buf+0xcf1/0x2d20 drivers/net/hamradio/6pack.c:413
 sixpack_decode drivers/net/hamradio/6pack.c:891 [inline]
 sixpack_receive_buf+0xcf1/0x2d20 drivers/net/hamradio/6pack.c:413
 tty_ldisc_receive_buf+0x1f7/0x2c0 drivers/tty/tty_buffer.c:391
 tty_port_default_receive_buf+0xd7/0x1a0 drivers/tty/tty_port.c:37
 receive_buf drivers/tty/tty_buffer.c:445 [inline]
 flush_to_ldisc+0x43e/0xe30 drivers/tty/tty_buffer.c:495
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0xb91/0x1d80 kernel/workqueue.c:3346
 worker_thread+0xedf/0x1590 kernel/workqueue.c:3427
 kthread+0xd5c/0xf00 kernel/kthread.c:463
 ret_from_fork+0x1f5/0x4c0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Uninit was created at:
 slab_post_alloc_hook mm/slub.c:4985 [inline]
 slab_alloc_node mm/slub.c:5288 [inline]
 __do_kmalloc_node mm/slub.c:5649 [inline]
 __kmalloc_noprof+0xabb/0x1b40 mm/slub.c:5662
 kmalloc_noprof include/linux/slab.h:961 [inline]
 tty_buffer_alloc drivers/tty/tty_buffer.c:180 [inline]
 __tty_buffer_request_room+0x3d4/0x7a0 drivers/tty/tty_buffer.c:273
 __tty_insert_flip_string_flags+0x157/0x6f0 drivers/tty/tty_buffer.c:309
 tty_insert_flip_char include/linux/tty_flip.h:77 [inline]
 uart_insert_char+0x368/0x930 drivers/tty/serial/serial_core.c:3457
 serial8250_read_char+0x1ba/0x670 drivers/tty/serial/8250/8250_port.c:1641
 serial8250_rx_chars drivers/tty/serial/8250/8250_port.c:1658 [inline]
 serial8250_handle_irq+0x930/0x1110 drivers/tty/serial/8250/8250_port.c:1822
 serial8250_default_handle_irq+0x116/0x370 drivers/tty/serial/8250/8250_port.c:1846
 serial8250_interrupt+0xcb/0x430 drivers/tty/serial/8250/8250_core.c:82
 __handle_irq_event_percpu+0x11e/0xf80 kernel/irq/handle.c:203
 handle_irq_event_percpu kernel/irq/handle.c:240 [inline]
 handle_irq_event+0xe0/0x2a0 kernel/irq/handle.c:257
 handle_edge_irq+0x2a9/0xb50 kernel/irq/chip.c:855
 generic_handle_irq_desc include/linux/irqdesc.h:173 [inline]
 handle_irq arch/x86/kernel/irq.c:254 [inline]
 call_irq_handler arch/x86/kernel/irq.c:-1 [inline]
 __common_interrupt+0x9d/0x180 arch/x86/kernel/irq.c:325
 common_interrupt+0x4c/0xb0 arch/x86/kernel/irq.c:318
 asm_common_interrupt+0x2b/0x40 arch/x86/include/asm/idtentry.h:688

CPU: 1 UID: 0 PID: 13878 Comm: kworker/u8:21 Tainted: G        W           syzkaller #0 PREEMPT(none) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: events_unbound flush_to_ldisc
=====================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup