[syzbot] [serial?] KMSAN: uninit-value in n_tty_lookahead_flow_ctrl

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    d3fa86b1a7b4 Merge tag 'net-6.7-rc3' of git://git.kernel.o..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=10c3bcd8e80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e32016b84cf917ca
dashboard link: https://syzkaller.appspot.com/bug?extid=0015c7d1e68e7f61621d
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12abdea4e80000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=173b1c94e80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c785fb3c059b/disk-d3fa86b1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/142addbb8256/vmlinux-d3fa86b1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8e6d7e1c7b24/bzImage-d3fa86b1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0015c7d1e68e7f61621d@xxxxxxxxxxxxxxxxxxxxxxxxx

=====================================================
BUG: KMSAN: uninit-value in n_tty_lookahead_flow_ctrl+0x2cd/0x2f0 drivers/tty/n_tty.c:1516
 n_tty_lookahead_flow_ctrl+0x2cd/0x2f0 drivers/tty/n_tty.c:1516
 tty_port_default_lookahead_buf+0x142/0x200 drivers/tty/tty_port.c:59
 lookahead_bufs drivers/tty/tty_buffer.c:427 [inline]
 flush_to_ldisc+0x906/0xdc0 drivers/tty/tty_buffer.c:497
 process_one_work kernel/workqueue.c:2630 [inline]
 process_scheduled_works+0x104e/0x1e70 kernel/workqueue.c:2703
 worker_thread+0xf45/0x1490 kernel/workqueue.c:2784
 kthread+0x3ed/0x540 kernel/kthread.c:388
 ret_from_fork+0x66/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242

Uninit was created at:
 slab_post_alloc_hook+0x129/0xa70 mm/slab.h:768
 slab_alloc_node mm/slub.c:3478 [inline]
 __kmem_cache_alloc_node+0x5c9/0x970 mm/slub.c:3517
 __do_kmalloc_node mm/slab_common.c:1006 [inline]
 __kmalloc+0x121/0x3c0 mm/slab_common.c:1020
 kmalloc include/linux/slab.h:604 [inline]
 tty_buffer_alloc drivers/tty/tty_buffer.c:179 [inline]
 __tty_buffer_request_room+0x36e/0x6c0 drivers/tty/tty_buffer.c:272
 __tty_insert_flip_string_flags+0x140/0x560 drivers/tty/tty_buffer.c:308
 tty_insert_flip_char include/linux/tty_flip.h:77 [inline]
 uart_insert_char+0x39e/0xa00 drivers/tty/serial/serial_core.c:3494
 serial8250_read_char+0x1a2/0x5d0 drivers/tty/serial/8250/8250_port.c:1760
 serial8250_rx_chars drivers/tty/serial/8250/8250_port.c:1777 [inline]
 serial8250_handle_irq+0x77b/0xb30 drivers/tty/serial/8250/8250_port.c:1937
 serial8250_default_handle_irq+0x11a/0x2a0 drivers/tty/serial/8250/8250_port.c:1962
 serial8250_interrupt+0xc0/0x350 drivers/tty/serial/8250/8250_core.c:127
 __handle_irq_event_percpu+0x113/0xc90 kernel/irq/handle.c:158
 handle_irq_event_percpu kernel/irq/handle.c:193 [inline]
 handle_irq_event+0xef/0x2c0 kernel/irq/handle.c:210
 handle_edge_irq+0x341/0xf90 kernel/irq/chip.c:831
 generic_handle_irq_desc include/linux/irqdesc.h:161 [inline]
 handle_irq arch/x86/kernel/irq.c:238 [inline]
 __common_interrupt+0x94/0x1f0 arch/x86/kernel/irq.c:257
 common_interrupt+0x89/0xa0 arch/x86/kernel/irq.c:247
 asm_common_interrupt+0x2b/0x40 arch/x86/include/asm/idtentry.h:636

CPU: 0 PID: 1031 Comm: kworker/u4:7 Not tainted 6.7.0-rc2-syzkaller-00095-gd3fa86b1a7b4 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
Workqueue: events_unbound flush_to_ldisc
=====================================================


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