linux-kernel - [BUG] KASAN_ null-ptr-deref in h5_recv during HCI UART handling on Linux 6.18

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Message-ID: <4ae89f04.1423.19c2cf17a5c.Coremail.25181214217@stu.xidian.edu.cn>
Date: Thu, 5 Feb 2026 16:35:48 +0800 (GMT+08:00)
From: 王明煜 <25181214217@....xidian.edu.cn>
To: marcel@...tmann.org, luiz.dentz@...il.com
Cc: linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: [BUG] KASAN_ null-ptr-deref in h5_recv during HCI UART handling on
 Linux 6.18

Dear Maintainers,

When using our customized Syzkaller to fuzz the latest Linux kernel, the following crash was triggered.

HEAD commit:7d0a66e4bb9081d75c82ec4957c50034cb0ea449
git tree: upstream
Output:https://github.com/manual0/crash/blob/main/report_8250_lpss.txt
Kernel config: https://github.com/manual0/crash/blob/main/config_syzbot.txt
C reproducer:https://github.com/manual0/crash/blob/main/repro_8250_lpss.c
Syz reproducer:https://github.com/manual0/crash/blob/main/repro_8250_lpss.syz

KASAN reports a null-pointer dereference in h5_recv within drivers/bluetooth/hci_h5.c when processing HCI UART input. The issue is triggered during normal ioctl/syscall paths while receiving data via hci_uart_tty_receive. This indicates that a pointer was unexpectedly NULL when dereferenced, leading to a general protection fault on a non-canonical address. The bug is consistently reproducible with our Syzkaller fuzzing setup and affects the Bluetooth H5 driver stack on Linux 6.18.

Oops: general protection fault, probably for non-canonical address 0xdffffc000000005f: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x00000000000002f8-0x00000000000002ff]
CPU: 0 UID: 0 PID: 108263 Comm: syz.1.9803 Not tainted 6.18.0 #1 PREEMPT(full) 
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
RIP: 0010:h5_recv+0xfc/0x8f0 home/wmy/Fuzzer/third_tool/linux-6.18/drivers/bluetooth/hci_h5.c:572
Code: c1 e8 03 4c 01 f0 48 89 44 24 08 48 8d 83 08 03 00 00 48 89 44 24 30 48 c1 e8 03 48 89 44 24 10 e8 69 cc 8f f9 48 8b 44 24 08 <80> 38 00 0f 85 a7 01 00 00 48 89 ea 48 89 e9 48 8b 83 f8 02 00 00
RSP: 0018:ffffc90007bafbe8 EFLAGS: 00010212
RAX: dffffc000000005f RBX: 0000000000000000 RCX: ffffc900142e2000
RDX: 0000000000080000 RSI: ffffffff882a8b97 RDI: 0000000000000005
RBP: ffffc90007bafd78 R08: 0000000000000000 R09: ffffed10073de083
R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000001
R13: 0000000000000001 R14: dffffc0000000000 R15: ffff888039ef0400
FS:  00007f69530e2640(0000) GS:ffff8880cf001000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000036b60000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 hci_uart_tty_receive+0x25b/0x800 home/wmy/Fuzzer/third_tool/linux-6.18/drivers/bluetooth/hci_ldisc.c:627
 tiocsti home/wmy/Fuzzer/third_tool/linux-6.18/drivers/tty/tty_io.c:2290 [inline]
 tty_ioctl+0x502/0x1690 home/wmy/Fuzzer/third_tool/linux-6.18/drivers/tty/tty_io.c:2706
 vfs_ioctl home/wmy/Fuzzer/third_tool/linux-6.18/fs/ioctl.c:51 [inline]
 __do_sys_ioctl home/wmy/Fuzzer/third_tool/linux-6.18/fs/ioctl.c:597 [inline]
 __se_sys_ioctl home/wmy/Fuzzer/third_tool/linux-6.18/fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x18f/0x210 home/wmy/Fuzzer/third_tool/linux-6.18/fs/ioctl.c:583
 do_syscall_x64 home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcb/0xfa0 home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f69521b059d
Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f69530e1f98 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f6952425fa0 RCX: 00007f69521b059d
RDX: 0000200000000080 RSI: 0000000000005412 RDI: 000000000000000c
RBP: 00007f695224e078 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6952426038 R14: 00007f6952425fa0 R15: 00007f69530c2000
 </TASK>

Thanks,
Mingyu Wang