[Android 6.1] KASAN: null-ptr-deref Write in remove_waiter

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Jul 12, 2026, 6:10:36 AM (8 days ago) Jul 12
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Hello,

syzbot found the following issue on:

HEAD commit: 21b931853e8d BACKPORT: usb: host: xhci-plat: Parse xhci-mi..
git tree: android14-6.1
console output: https://syzkaller.appspot.com/x/log.txt?x=1081d432580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6af0777879025b2
dashboard link: https://syzkaller.appspot.com/bug?extid=ed2a857004831718796a
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16f5f0b9580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1047a0b9580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/81f79235bd78/disk-21b93185.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7536bd278b6c/vmlinux-21b93185.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4c749a817ee2/bzImage-21b93185.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ed2a85...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
BUG: KASAN: null-ptr-deref in atomic_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:541 [inline]
BUG: KASAN: null-ptr-deref in queued_spin_lock include/asm-generic/qspinlock.h:111 [inline]
BUG: KASAN: null-ptr-deref in do_raw_spin_lock include/linux/spinlock.h:187 [inline]
BUG: KASAN: null-ptr-deref in __raw_spin_lock include/linux/spinlock_api_smp.h:134 [inline]
BUG: KASAN: null-ptr-deref in _raw_spin_lock+0x87/0xf0 kernel/locking/spinlock.c:154
Write of size 4 at addr 0000000000000904 by task syz.6.86/677

CPU: 1 PID: 677 Comm: syz.6.86 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Call Trace:
<TASK>
__dump_stack+0x21/0x24 lib/dump_stack.c:88
dump_stack_lvl+0x110/0x170 lib/dump_stack.c:106
print_report+0x3d/0x60 mm/kasan/report.c:423
kasan_report+0x122/0x150 mm/kasan/report.c:524
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x249/0x2a0 mm/kasan/generic.c:189
__kasan_check_write+0x14/0x20 mm/kasan/shadow.c:37
instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
atomic_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:541 [inline]
queued_spin_lock include/asm-generic/qspinlock.h:111 [inline]
do_raw_spin_lock include/linux/spinlock.h:187 [inline]
__raw_spin_lock include/linux/spinlock_api_smp.h:134 [inline]
_raw_spin_lock+0x87/0xf0 kernel/locking/spinlock.c:154
class_raw_spinlock_constructor include/linux/spinlock.h:498 [inline]
remove_waiter+0xdd/0x750 kernel/locking/rtmutex.c:1478
rt_mutex_start_proxy_lock+0x40/0xb0 kernel/locking/rtmutex_api.c:353
futex_requeue+0xff4/0x1330 kernel/futex/requeue.c:629
do_futex+0x25e/0x430 kernel/futex/syscalls.c:-1
__do_sys_futex kernel/futex/syscalls.c:213 [inline]
__se_sys_futex+0x136/0x310 kernel/futex/syscalls.c:194
__x64_sys_futex+0xe5/0x100 kernel/futex/syscalls.c:194
x64_sys_call+0x7ec/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:203
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f37a959de59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f37aa4a7028 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: ffffffffffffffda RBX: 00007f37a9826180 RCX: 00007f37a959de59
RDX: 0000000000000001 RSI: 000000000000000c RDI: 000020000000cffc
RBP: 00007f37a9633e6f R08: 0000200000048000 R09: 0000000000000000
R10: 0000200000000040 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f37a9826218 R14: 00007f37a9826180 R15: 00007ffd6376b508
</TASK>
==================================================================
BUG: kernel NULL pointer dereference, address: 0000000000000904
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 11ca71067 P4D 11ca71067 PUD 0
Oops: 0002 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 677 Comm: syz.6.86 Tainted: G B syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:arch_atomic_try_cmpxchg arch/x86/include/asm/atomic.h:202 [inline]
RIP: 0010:atomic_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:543 [inline]
RIP: 0010:queued_spin_lock include/asm-generic/qspinlock.h:111 [inline]
RIP: 0010:do_raw_spin_lock include/linux/spinlock.h:187 [inline]
RIP: 0010:__raw_spin_lock include/linux/spinlock_api_smp.h:134 [inline]
RIP: 0010:_raw_spin_lock+0x9d/0xf0 kernel/locking/spinlock.c:154
Code: 44 24 20 00 00 00 00 48 89 df be 04 00 00 00 e8 89 f6 b5 fc 4c 89 f7 be 04 00 00 00 e8 7c f6 b5 fc 8b 44 24 20 b9 01 00 00 00 <f0> 0f b1 0b 75 33 43 c6 44 27 04 f8 48 c7 04 24 0e 36 e0 45 4b c7
RSP: 0018:ffffc900015ff940 EFLAGS: 00010097
RAX: 0000000000000000 RBX: 0000000000000904 RCX: 0000000000000001
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffc900015ff960
RBP: ffffc900015ff9d0 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520002bff2c R12: dffffc0000000000
R13: ffff88811b6b6f20 R14: ffffc900015ff960 R15: 1ffff920002bff28
FS: 00007f37aa4a76c0(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000904 CR3: 000000011d6ca000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
class_raw_spinlock_constructor include/linux/spinlock.h:498 [inline]
remove_waiter+0xdd/0x750 kernel/locking/rtmutex.c:1478
rt_mutex_start_proxy_lock+0x40/0xb0 kernel/locking/rtmutex_api.c:353
futex_requeue+0xff4/0x1330 kernel/futex/requeue.c:629
do_futex+0x25e/0x430 kernel/futex/syscalls.c:-1
__do_sys_futex kernel/futex/syscalls.c:213 [inline]
__se_sys_futex+0x136/0x310 kernel/futex/syscalls.c:194
__x64_sys_futex+0xe5/0x100 kernel/futex/syscalls.c:194
x64_sys_call+0x7ec/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:203
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f37a959de59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f37aa4a7028 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: ffffffffffffffda RBX: 00007f37a9826180 RCX: 00007f37a959de59
RDX: 0000000000000001 RSI: 000000000000000c RDI: 000020000000cffc
RBP: 00007f37a9633e6f R08: 0000200000048000 R09: 0000000000000000
R10: 0000200000000040 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f37a9826218 R14: 00007f37a9826180 R15: 00007ffd6376b508
</TASK>
Modules linked in:
CR2: 0000000000000904
---[ end trace 0000000000000000 ]---
RIP: 0010:arch_atomic_try_cmpxchg arch/x86/include/asm/atomic.h:202 [inline]
RIP: 0010:atomic_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:543 [inline]
RIP: 0010:queued_spin_lock include/asm-generic/qspinlock.h:111 [inline]
RIP: 0010:do_raw_spin_lock include/linux/spinlock.h:187 [inline]
RIP: 0010:__raw_spin_lock include/linux/spinlock_api_smp.h:134 [inline]
RIP: 0010:_raw_spin_lock+0x9d/0xf0 kernel/locking/spinlock.c:154
Code: 44 24 20 00 00 00 00 48 89 df be 04 00 00 00 e8 89 f6 b5 fc 4c 89 f7 be 04 00 00 00 e8 7c f6 b5 fc 8b 44 24 20 b9 01 00 00 00 <f0> 0f b1 0b 75 33 43 c6 44 27 04 f8 48 c7 04 24 0e 36 e0 45 4b c7
RSP: 0018:ffffc900015ff940 EFLAGS: 00010097
RAX: 0000000000000000 RBX: 0000000000000904 RCX: 0000000000000001
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffc900015ff960
RBP: ffffc900015ff9d0 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520002bff2c R12: dffffc0000000000
R13: ffff88811b6b6f20 R14: ffffc900015ff960 R15: 1ffff920002bff28
FS: 00007f37aa4a76c0(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000904 CR3: 000000011d6ca000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
0: 44 24 20 rex.R and $0x20,%al
3: 00 00 add %al,(%rax)
5: 00 00 add %al,(%rax)
7: 48 89 df mov %rbx,%rdi
a: be 04 00 00 00 mov $0x4,%esi
f: e8 89 f6 b5 fc call 0xfcb5f69d
14: 4c 89 f7 mov %r14,%rdi
17: be 04 00 00 00 mov $0x4,%esi
1c: e8 7c f6 b5 fc call 0xfcb5f69d
21: 8b 44 24 20 mov 0x20(%rsp),%eax
25: b9 01 00 00 00 mov $0x1,%ecx
* 2a: f0 0f b1 0b lock cmpxchg %ecx,(%rbx) <-- trapping instruction
2e: 75 33 jne 0x63
30: 43 c6 44 27 04 f8 movb $0xf8,0x4(%r15,%r12,1)
36: 48 c7 04 24 0e 36 e0 movq $0x45e0360e,(%rsp)
3d: 45
3e: 4b rex.WXB
3f: c7 .byte 0xc7


---
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