[syzbot] [serial?] KMSAN: uninit-value in gsmld_receive_buf (2)

[syzbot <syzbot+60e074cc0d3b54a82cf1@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    cf38b2340c0e Merge tag 'soc-fixes-6.19-2' of git://git.ker..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15e05d22580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8bf02b9e495b9fcd
dashboard link: https://syzkaller.appspot.com/bug?extid=60e074cc0d3b54a82cf1
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0bca22500a65/disk-cf38b234.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7d7caf81eafb/vmlinux-cf38b234.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d9e3619531e9/bzImage-cf38b234.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+60e074cc0d3b54a82cf1@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in gsmld_receive_buf+0x558/0x5d0 drivers/tty/n_gsm.c:3617
 gsmld_receive_buf+0x558/0x5d0 drivers/tty/n_gsm.c:3617
 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/0xe40 drivers/tty/tty_buffer.c:495
 process_one_work kernel/workqueue.c:3257 [inline]
 process_scheduled_works+0xb03/0x1da0 kernel/workqueue.c:3340
 worker_thread+0xede/0x1590 kernel/workqueue.c:3421
 kthread+0xd5a/0xf00 kernel/kthread.c:463
 ret_from_fork+0x207/0x6f0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

Uninit was created at:
 slab_post_alloc_hook mm/slub.c:4960 [inline]
 slab_alloc_node mm/slub.c:5263 [inline]
 __do_kmalloc_node mm/slub.c:5656 [inline]
 __kmalloc_noprof+0xae9/0x1c00 mm/slub.c:5669
 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:3423
 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/0x420 drivers/tty/serial/8250/8250_core.c:86
 __handle_irq_event_percpu+0x118/0xec0 kernel/irq/handle.c:211
 handle_irq_event_percpu kernel/irq/handle.c:248 [inline]
 handle_irq_event+0xe0/0x2a0 kernel/irq/handle.c:265
 handle_edge_irq+0x2a9/0xb50 kernel/irq/chip.c:855
 generic_handle_irq_desc include/linux/irqdesc.h:172 [inline]
 handle_irq arch/x86/kernel/irq.c:255 [inline]
 call_irq_handler arch/x86/kernel/irq.c:-1 [inline]
 __common_interrupt+0x9d/0x180 arch/x86/kernel/irq.c:326
 common_interrupt+0x94/0xb0 arch/x86/kernel/irq.c:319
 asm_common_interrupt+0x2b/0x40 arch/x86/include/asm/idtentry.h:688

CPU: 1 UID: 0 PID: 6065 Comm: kworker/u8:16 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: events_unbound flush_to_ldisc
=====================================================


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