KASAN: slab-use-after-free Read in nr_add_node

Status: upstream: reported syz repro on 2025/09/18 05:23
Bug presence: origin:upstream
Labels: missing-backport
[Documentation on labels]
Reported-by: syzbot+bc816d17a19282db7bb3@syzkaller.appspotmail.com
First crash: 317d, last: 317d
Fix bisection: failed (error log, bisect log)
  
▶ ▼ Bug presence (3)
Date Name Commit Repro Result
2026/05/27 linux-6.6.y (ToT) 0a40c6fbd105 syz [report] possible deadlock in nr_rt_device_down
2025/09/19 upstream (ToT) 097a6c336d00 syz [report] possible deadlock in nr_rt_device_down
2026/05/27 upstream (ToT) eb3f4b7426cf syz Didn't crash
▶ ▼ Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: slab-use-after-free Read in nr_add_node prio:normal hams 19 syz, C error error 6 109d 309d 0/29 upstream: reported C repro on 2025/09/25 16:35
linux-6.1 KASAN: use-after-free Read in nr_add_node 19 1 507d 507d 0/3 auto-obsoleted due to no activity on 2025/06/19 16:48
linux-6.1 KASAN: use-after-free Read in nr_add_node (2) origin:upstream 19 syz, C error 1 216d 317d 0/3 upstream: reported C repro on 2025/09/18 05:54
linux-5.15 KASAN: use-after-free Read in nr_add_node origin:upstream 19 syz, C error 1 5d06h 556d 0/3 upstream: reported C repro on 2025/01/22 09:11
▶ ▼ Fix bisection attempts (2)
Created Duration User Patch Repo Result
2026/06/08 02:13 13m fix candidate upstream error job log
2026/01/22 02:58 0m bisect fix linux-6.6.y error job log

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in nr_add_node+0x2455/0x24b0 net/netrom/nr_route.c:248
Read of size 2 at addr ffff88805bffd332 by task syz.3.1722/9436

CPU: 1 PID: 9436 Comm: syz.3.1722 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x16c/0x230 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:364 [inline]
 print_report+0xac/0x220 mm/kasan/report.c:468
 kasan_report+0x117/0x150 mm/kasan/report.c:581
 nr_add_node+0x2455/0x24b0 net/netrom/nr_route.c:248
 nr_rt_ioctl+0xc0f/0xd40 net/netrom/nr_route.c:651
 sock_do_ioctl+0xd7/0x2f0 net/socket.c:1222
 sock_ioctl+0x623/0x7a0 net/socket.c:1341
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f547dd8eba9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f547eb3b038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f547dfd5fa0 RCX: 00007f547dd8eba9
RDX: 0000200000000000 RSI: 000000000000890b RDI: 0000000000000004
RBP: 00007f547de11e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f547dfd6038 R14: 00007f547dfd5fa0 R15: 00007fff2d313028
 </TASK>

Allocated by task 9440:
 kasan_save_stack mm/kasan/common.c:45 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:52
 ____kasan_kmalloc mm/kasan/common.c:374 [inline]
 __kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:383
 kmalloc include/linux/slab.h:600 [inline]
 nr_add_node+0x7f9/0x24b0 net/netrom/nr_route.c:146
 nr_rt_ioctl+0xc0f/0xd40 net/netrom/nr_route.c:651
 sock_do_ioctl+0xd7/0x2f0 net/socket.c:1222
 sock_ioctl+0x623/0x7a0 net/socket.c:1341
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Freed by task 9436:
 kasan_save_stack mm/kasan/common.c:45 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:52
 kasan_save_free_info+0x2e/0x50 mm/kasan/generic.c:522
 ____kasan_slab_free+0x126/0x1e0 mm/kasan/common.c:236
 kasan_slab_free include/linux/kasan.h:164 [inline]
 slab_free_hook mm/slub.c:1811 [inline]
 slab_free_freelist_hook+0x130/0x1b0 mm/slub.c:1837
 slab_free mm/slub.c:3830 [inline]
 __kmem_cache_free+0xba/0x1f0 mm/slub.c:3843
 nr_add_node+0x1c40/0x24b0 net/netrom/nr_route.c:246
 nr_rt_ioctl+0xc0f/0xd40 net/netrom/nr_route.c:651
 sock_do_ioctl+0xd7/0x2f0 net/socket.c:1222
 sock_ioctl+0x623/0x7a0 net/socket.c:1341
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff88805bffd300
 which belongs to the cache kmalloc-64 of size 64
The buggy address is located 50 bytes inside of
 freed 64-byte region [ffff88805bffd300, ffff88805bffd340)

The buggy address belongs to the physical page:
page:ffffea00016fff40 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x5bffd
ksm flags: 0xfff00000000800(slab|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000800 ffff888017841640 ffffea0001663400 dead000000000007
raw: 0000000000000000 0000000000200020 00000001ffffffff 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 0x112cc0(GFP_USER|__GFP_NOWARN|__GFP_NORETRY), pid 5809, tgid 5809 (syz-executor), ts 93104503711, free_ts 27330338935
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x1cd/0x210 mm/page_alloc.c:1554
 prep_new_page mm/page_alloc.c:1561 [inline]
 get_page_from_freelist+0x195c/0x19f0 mm/page_alloc.c:3191
 __alloc_pages+0x1e3/0x460 mm/page_alloc.c:4457
 alloc_slab_page+0x5d/0x170 mm/slub.c:1881
 allocate_slab mm/slub.c:2028 [inline]
 new_slab+0x87/0x2e0 mm/slub.c:2081
 ___slab_alloc+0xc6d/0x1300 mm/slub.c:3253
 __slab_alloc mm/slub.c:3339 [inline]
 __slab_alloc_node mm/slub.c:3392 [inline]
 slab_alloc_node mm/slub.c:3485 [inline]
 __kmem_cache_alloc_node+0x1a2/0x260 mm/slub.c:3534
 __do_kmalloc_node mm/slab_common.c:1006 [inline]
 __kmalloc+0xa4/0x240 mm/slab_common.c:1020
 kmalloc include/linux/slab.h:604 [inline]
 kzalloc include/linux/slab.h:721 [inline]
 kobject_get_path+0xc3/0x2c0 lib/kobject.c:161
 kobject_uevent_env+0x28a/0x8c0 lib/kobject_uevent.c:544
 rx_queue_add_kobject net/core/net-sysfs.c:1101 [inline]
 net_rx_queue_update_kobjects+0x313/0x580 net/core/net-sysfs.c:1141
 register_queue_kobjects net/core/net-sysfs.c:1801 [inline]
 netdev_register_kobject+0x227/0x310 net/core/net-sysfs.c:2046
 register_netdevice+0x128f/0x1ae0 net/core/dev.c:10280
 register_netdev+0x3b/0x50 net/core/dev.c:10412
 vti6_init_net+0x214/0x330 net/ipv6/ip6_vti.c:1163
 ops_init+0x397/0x640 net/core/net_namespace.c:139
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1154 [inline]
 free_unref_page_prepare+0x7ce/0x8e0 mm/page_alloc.c:2336
 free_unref_page+0x32/0x2e0 mm/page_alloc.c:2429
 free_contig_range+0xa1/0x160 mm/page_alloc.c:6369
 destroy_args+0x80/0x850 mm/debug_vm_pgtable.c:1015
 debug_vm_pgtable+0x3cc/0x410 mm/debug_vm_pgtable.c:1400
 do_one_initcall+0x1fd/0x750 init/main.c:1238
 do_initcall_level+0x137/0x1f0 init/main.c:1300
 do_initcalls+0x69/0xd0 init/main.c:1316
 kernel_init_freeable+0x3d2/0x570 init/main.c:1553
 kernel_init+0x1d/0x1c0 init/main.c:1443
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293

Memory state around the buggy address:
 ffff88805bffd200: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff88805bffd280: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>ffff88805bffd300: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                                     ^
 ffff88805bffd380: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff88805bffd400: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/09/18 05:22 linux-6.6.y 60a9e718726f e2beed91 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in nr_add_node
* Struck through repros no longer work on HEAD.