KASAN: null-ptr-deref Write in remove_waiter

Status: premoderation: reported C repro on 2026/07/20 12:54
Bug presence: origin:upstream
[Documentation on labels]
Reported-by: syzbot+70939aa6360eaed17ac9@syzkaller.appspotmail.com
First crash: 5d08h, last: 5d06h
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2026/07/20 lts (merge base) 51eba7e6c91a C [report] lost connection to test machine
2026/07/20 upstream (ToT) 1590cf032971 C [report] lost connection to test machine
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-6-1 KASAN: null-ptr-deref Write in remove_waiter 12 C 1 13d 13d 0/2 upstream: reported C repro on 2026/07/12 10:10
upstream general protection fault in remove_waiter prio:high kernel 2 syz 6 76d 88d 29/29 fixed on 2026/07/15 08:27

Sample crash report:
==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
BUG: KASAN: null-ptr-deref in atomic_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:1300 [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+0x85/0x120 kernel/locking/spinlock.c:154
Write of size 4 at addr 000000000000094c by task syz.2.49/516

CPU: 1 UID: 0 PID: 516 Comm: syz.2.49 Not tainted syzkaller #0 68e3201df5fdad0ba521b4874bccf43aba0ac9cd
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/25/2026
Call Trace:
 <TASK>
 __dump_stack+0x21/0x30 lib/dump_stack.c:94
 dump_stack_lvl+0x140/0x1c0 lib/dump_stack.c:120
 print_report+0x3d/0x70 mm/kasan/report.c:484
 kasan_report+0x162/0x1a0 mm/kasan/report.c:594
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x25a/0x2b0 mm/kasan/generic.c:189
 __kasan_check_write+0x18/0x20 mm/kasan/shadow.c:37
 instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
 atomic_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:1300 [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+0x85/0x120 kernel/locking/spinlock.c:154
 class_raw_spinlock_constructor include/linux/spinlock.h:536 [inline]
 remove_waiter+0xdc/0x740 kernel/locking/rtmutex.c:1552
 rt_mutex_start_proxy_lock+0xf7/0x1f0 kernel/locking/rtmutex_api.c:356
 futex_requeue+0x10a5/0x1450 kernel/futex/requeue.c:633
 do_futex+0x354/0x510 kernel/futex/syscalls.c:-1
 __do_sys_futex kernel/futex/syscalls.c:209 [inline]
 __se_sys_futex+0x13c/0x320 kernel/futex/syscalls.c:190
 __x64_sys_futex+0xe9/0x110 kernel/futex/syscalls.c:190
 x64_sys_call+0x227f/0x2ee0 arch/x86/include/generated/asm/syscalls_64.h:203
 do_syscall_x64 arch/x86/entry/common.c:47 [inline]
 do_syscall_64+0x57/0xf0 arch/x86/entry/common.c:78
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7fc66919de99
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:00007fc668fbd028 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: ffffffffffffffda RBX: 00007fc669426180 RCX: 00007fc66919de99
RDX: 0000000000000001 RSI: 000000000000000c RDI: 000020000000cffc
RBP: 00007fc669233eaf R08: 0000200000048000 R09: 0000000000000000
R10: 0000200000000040 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc669426218 R14: 00007fc669426180 R15: 00007ffe5e797f98
 </TASK>
==================================================================
BUG: kernel NULL pointer dereference, address: 000000000000094c
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 8000000116d6d067 P4D 8000000116d6d067 PUD 0 
Oops: Oops: 0002 [#1] PREEMPT SMP KASAN PTI
CPU: 1 UID: 0 PID: 516 Comm: syz.2.49 Tainted: G    B              syzkaller #0 68e3201df5fdad0ba521b4874bccf43aba0ac9cd
Tainted: [B]=BAD_PAGE
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/25/2026
RIP: 0010:arch_atomic_try_cmpxchg arch/x86/include/asm/atomic.h:107 [inline]
RIP: 0010:raw_atomic_try_cmpxchg_acquire include/linux/atomic/atomic-arch-fallback.h:2170 [inline]
RIP: 0010:atomic_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:1302 [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+0x9b/0x120 kernel/locking/spinlock.c:154
Code: 04 04 c7 44 24 20 00 00 00 00 be 04 00 00 00 e8 db 8c 3a fc 4c 89 f7 be 04 00 00 00 e8 ce 8c 3a fc 8b 44 24 20 b9 01 00 00 00 <f0> 0f b1 0b 75 38 43 c6 44 3c 04 f8 48 c7 04 24 0e 36 e0 45 4b c7
RSP: 0018:ffffc90000dff880 EFLAGS: 00010097
RAX: 0000000000000000 RBX: 000000000000094c RCX: 0000000000000001
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffc90000dff8a0
RBP: ffffc90000dff910 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520001bff14 R12: 1ffff920001bff10
R13: ffff888117a7a628 R14: ffffc90000dff8a0 R15: dffffc0000000000
FS:  00007fc668fbd6c0(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000000094c CR3: 0000000117f36000 CR4: 00000000003526b0
Call Trace:
 <TASK>
 class_raw_spinlock_constructor include/linux/spinlock.h:536 [inline]
 remove_waiter+0xdc/0x740 kernel/locking/rtmutex.c:1552
 rt_mutex_start_proxy_lock+0xf7/0x1f0 kernel/locking/rtmutex_api.c:356
 futex_requeue+0x10a5/0x1450 kernel/futex/requeue.c:633
 do_futex+0x354/0x510 kernel/futex/syscalls.c:-1
 __do_sys_futex kernel/futex/syscalls.c:209 [inline]
 __se_sys_futex+0x13c/0x320 kernel/futex/syscalls.c:190
 __x64_sys_futex+0xe9/0x110 kernel/futex/syscalls.c:190
 x64_sys_call+0x227f/0x2ee0 arch/x86/include/generated/asm/syscalls_64.h:203
 do_syscall_x64 arch/x86/entry/common.c:47 [inline]
 do_syscall_64+0x57/0xf0 arch/x86/entry/common.c:78
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7fc66919de99
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:00007fc668fbd028 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: ffffffffffffffda RBX: 00007fc669426180 RCX: 00007fc66919de99
RDX: 0000000000000001 RSI: 000000000000000c RDI: 000020000000cffc
RBP: 00007fc669233eaf R08: 0000200000048000 R09: 0000000000000000
R10: 0000200000000040 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc669426218 R14: 00007fc669426180 R15: 00007ffe5e797f98
 </TASK>
Modules linked in:
CR2: 000000000000094c
---[ end trace 0000000000000000 ]---
RIP: 0010:arch_atomic_try_cmpxchg arch/x86/include/asm/atomic.h:107 [inline]
RIP: 0010:raw_atomic_try_cmpxchg_acquire include/linux/atomic/atomic-arch-fallback.h:2170 [inline]
RIP: 0010:atomic_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:1302 [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+0x9b/0x120 kernel/locking/spinlock.c:154
Code: 04 04 c7 44 24 20 00 00 00 00 be 04 00 00 00 e8 db 8c 3a fc 4c 89 f7 be 04 00 00 00 e8 ce 8c 3a fc 8b 44 24 20 b9 01 00 00 00 <f0> 0f b1 0b 75 38 43 c6 44 3c 04 f8 48 c7 04 24 0e 36 e0 45 4b c7
RSP: 0018:ffffc90000dff880 EFLAGS: 00010097
RAX: 0000000000000000 RBX: 000000000000094c RCX: 0000000000000001
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffc90000dff8a0
RBP: ffffc90000dff910 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520001bff14 R12: 1ffff920001bff10
R13: ffff888117a7a628 R14: ffffc90000dff8a0 R15: dffffc0000000000
FS:  00007fc668fbd6c0(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000000094c CR3: 0000000117f36000 CR4: 00000000003526b0
----------------
Code disassembly (best guess):
   0:	04 04                	add    $0x4,%al
   2:	c7 44 24 20 00 00 00 	movl   $0x0,0x20(%rsp)
   9:	00
   a:	be 04 00 00 00       	mov    $0x4,%esi
   f:	e8 db 8c 3a fc       	call   0xfc3a8cef
  14:	4c 89 f7             	mov    %r14,%rdi
  17:	be 04 00 00 00       	mov    $0x4,%esi
  1c:	e8 ce 8c 3a fc       	call   0xfc3a8cef
  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 38                	jne    0x68
  30:	43 c6 44 3c 04 f8    	movb   $0xf8,0x4(%r12,%r15,1)
  36:	48 c7 04 24 0e 36 e0 	movq   $0x45e0360e,(%rsp)
  3d:	45
  3e:	4b                   	rex.WXB
  3f:	c7                   	.byte 0xc7

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/20 14:38 android16-6.12 c3f9cafa739b de6a700d .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust KASAN: null-ptr-deref Write in remove_waiter
2026/07/20 12:53 android16-6.12 c3f9cafa739b de6a700d .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust KASAN: null-ptr-deref Write in remove_waiter
* Struck through repros no longer work on HEAD.