KASAN: slab-use-after-free Write in nr_neigh_put

Status: auto-obsoleted due to no activity on 2026/07/22 20:36
Subsystems: hams
Labels: prio:normal
[Documentation on labels]
Reported-by: syzbot+08ca620c862d89afe6d6@syzkaller.appspotmail.com
First crash: 173d, last: 101d
▶ ▼ ✨ AI Jobs (3)
ID Workflow Result Correct Bug Created Started Finished Revision Error
60db4fa0-e41f-41fd-a511-47bee0cda1dc repro-c Reproduced: ✅ ❓ KASAN: slab-use-after-free Write in nr_neigh_put 2026/05/26 10:35 2026/05/26 10:41 2026/05/26 11:40 c69befb30ac10e158cc9d1557b508ee3f0eca1de 

			
				
	

	
	

		752cb8f7-f75f-427e-abd9-485c496e75e8
		assessment-security
		
			
				
					DenialOfService: ✅
				
			
				
					Exploitable: ✅
				
			
				
					FilesystemTrigger: ❌
				
			
				
					NetworkTrigger: ❌
				
			
				
					PeripheralTrigger: ❌
				
			
				
					RemoteTrigger: ❌
				
			
				
					Unprivileged: ❌
				
			
				
					UserNamespace: ❌
				
			
				
					VMGuestTrigger: ❌
				
			
				
					VMHostTrigger: ❌
				
			
				
			
		
		❓
		KASAN: slab-use-after-free Write in nr_neigh_put
		2026/05/15 18:55
		2026/05/15 18:55
		2026/05/15 19:42
		efdaf0f9b8bfc56ea6d17bea15a64f4591cc712d
		
			

			
				
	

	
	

		b05afe00-6886-48a2-be50-5d7430f1c330
		repro
		
			
				
			
				
			
				
			
		
		❓
		KASAN: slab-use-after-free Write in nr_neigh_put
		2026/03/07 16:27
		2026/03/07 16:27
		2026/03/07 16:39
		31e9c887f7dc24e04b3ca70d0d54fc34141844b0
		
			

			
				
	

	
	



			

		

	

	
	

		

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			[syzbot] [hams?] KASAN: slab-use-after-free Write in nr_neigh_put
			0 (1)
			2026/01/31 09:49
		

	
	




			
			
		

	

	

	
	
Sample crash report:

	
==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
BUG: KASAN: slab-use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
BUG: KASAN: slab-use-after-free in __refcount_sub_and_test include/linux/refcount.h:389 [inline]
BUG: KASAN: slab-use-after-free in __refcount_dec_and_test include/linux/refcount.h:432 [inline]
BUG: KASAN: slab-use-after-free in refcount_dec_and_test include/linux/refcount.h:450 [inline]
BUG: KASAN: slab-use-after-free in nr_neigh_put+0x21/0x170 include/net/netrom.h:139
Write of size 4 at addr ffff888028dc0ebc by task syz.3.4420/22103

CPU: 1 UID: 0 PID: 22103 Comm: syz.3.4420 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
 instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
 atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
 __refcount_sub_and_test include/linux/refcount.h:389 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 nr_neigh_put+0x21/0x170 include/net/netrom.h:139
 nr_del_neigh+0x25a/0x2d0 net/netrom/nr_route.c:440
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5a8e59c819
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:00007f5a8f3c3028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f5a8e815fa0 RCX: 00007f5a8e59c819
RDX: 0000200000000740 RSI: 000000000000890c RDI: 000000000000000b
RBP: 00007f5a8e632c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5a8e816038 R14: 00007f5a8e815fa0 R15: 00007fff4f4442c8
 </TASK>

Allocated by task 20448:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x31c/0x660 mm/slub.c:5380
 kmalloc_noprof include/linux/slab.h:950 [inline]
 nr_add_neigh+0x104/0x520 net/netrom/nr_route.c:392
 nr_rt_ioctl+0xdf9/0xf90 net/netrom/nr_route.c:660
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 22103:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2685 [inline]
 slab_free mm/slub.c:6165 [inline]
 kfree+0x1c1/0x630 mm/slub.c:6483
 __nr_remove_neigh net/netrom/nr_route.c:299 [inline]
 nr_remove_neigh net/netrom/nr_route.c:308 [inline]
 nr_del_neigh+0x246/0x2d0 net/netrom/nr_route.c:439
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888028dc0e80
 which belongs to the cache kmalloc-64 of size 64
The buggy address is located 60 bytes inside of
 freed 64-byte region [ffff888028dc0e80, ffff888028dc0ec0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x28dc0
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff88813fea78c0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 36, tgid 36 (kworker/u8:2), ts 8945898703, free_ts 8878260428
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_slab_page mm/slub.c:3292 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3481
 new_slab mm/slub.c:3539 [inline]
 refill_objects+0x331/0x3c0 mm/slub.c:7175
 refill_sheaf mm/slub.c:2812 [inline]
 __pcs_replace_empty_main+0x2e6/0x730 mm/slub.c:4615
 alloc_from_pcs mm/slub.c:4717 [inline]
 slab_alloc_node mm/slub.c:4851 [inline]
 __do_kmalloc_node mm/slub.c:5259 [inline]
 __kmalloc_noprof+0x474/0x760 mm/slub.c:5272
 kmalloc_noprof include/linux/slab.h:954 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 lsm_blob_alloc security/security.c:193 [inline]
 lsm_task_alloc security/security.c:245 [inline]
 security_task_alloc+0x4d/0x330 security/security.c:2683
 copy_process+0x16df/0x3cd0 kernel/fork.c:2205
 kernel_clone+0x248/0x8e0 kernel/fork.c:2653
 user_mode_thread+0x110/0x180 kernel/fork.c:2729
 call_usermodehelper_exec_work+0x5c/0x230 kernel/umh.c:171
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
page last free pid 849 tgid 849 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1433 [inline]
 __free_frozen_pages+0xc2b/0xdb0 mm/page_alloc.c:2978
 vfree+0x25a/0x400 mm/vmalloc.c:3479
 delayed_vfree_work+0x55/0x80 mm/vmalloc.c:3398
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
 ffff888028dc0d80: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff888028dc0e00: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
>ffff888028dc0e80: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                                        ^
 ffff888028dc0f00: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff888028dc0f80: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
==================================================================



	

	



	Crashes (2):
		
		

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			2026/04/13 20:35
			net
			2dddb34dd0d0
			9530ccf9
			.config
			console log
			report
			
			
			info
			
				[disk image]
			
				[vmlinux]
			
				[kernel image]
			
			ci-upstream-net-this-kasan-gce
			KASAN: slab-use-after-free Write in nr_neigh_put
		

		
		

			2026/01/31 04:54
			net-next
			6ad42b244136
			e01a0ca6
			.config
			console log
			report
			
			
			info
			
				[disk image]
			
				[vmlinux]
			
				[kernel image]
			
			ci-upstream-net-kasan-gce
			KASAN: slab-use-after-free Write in nr_neigh_put
		

		
		


* Struck through repros no longer work on HEAD.