KASAN: use-after-free Read in vlan_dev_get_iflink

Status: upstream: reported C repro on 2025/10/31 17:51
Bug presence: origin:lts
[Documentation on labels]
Reported-by: syzbot+4234cb99239796b6887b@syzkaller.appspotmail.com
First crash: 715d, last: 108d
Fix bisection: failed (error log, bisect log)
  
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2025/11/04 lts (merge base) ac56c046adf4 C [report] KASAN: use-after-free Read in vlan_dev_get_iflink
2025/11/04 upstream (ToT) c9cfc122f037 C Didn't crash
▶ ▼ Similar bugs (6)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-4.19 KASAN: use-after-free Read in vlan_dev_get_iflink 19 syz, C error 18 1359d 2298d 0/1 upstream: reported C repro on 2020/04/13 08:02
linux-4.14 KASAN: use-after-free Read in vlan_dev_get_iflink 19 syz, C error 12 1422d 2285d 0/1 upstream: reported C repro on 2020/04/25 21:56
linux-5.15 KASAN: use-after-free Read in vlan_dev_get_iflink (2) 19 2 300d 317d 0/3 auto-obsoleted due to no activity on 2026/01/10 03:27
linux-5.15 KASAN: use-after-free Read in vlan_dev_get_iflink 19 4 698d 727d 0/3 auto-obsoleted due to no activity on 2024/12/07 21:23
upstream KASAN: use-after-free Read in vlan_dev_get_iflink net 19 syz, C error error 13 2027d 2197d 0/29 auto-obsoleted due to no activity on 2022/09/27 12:32
android-5-10 KASAN: use-after-free Read in vlan_dev_get_iflink 19 syz, C 50 2d02h 466d 0/2 upstream: reported C repro on 2025/04/19 07:52
▶ ▼ Last patch testing requests (6)
Created Duration User Patch Repo Result
2026/07/27 16:48 14m retest repro android13-5.15-lts log
2026/06/06 22:17 13m retest repro android13-5.15-lts log
2026/04/12 06:30 19m retest repro android13-5.15-lts report log
2026/03/13 04:06 6m retest repro android13-5.15-lts error
2026/01/24 04:24 13m retest repro android13-5.15-lts OK log
2026/01/02 02:54 9m retest repro android13-5.15-lts report log
▶ ▼ Fix bisection attempts (2)
Created Duration User Patch Repo Result
2026/02/01 04:06 4m bisect fix android13-5.15-lts error job log
2025/12/18 10:50 1h18m bisect fix android13-5.15-lts OK (0) job log log

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in vlan_dev_get_iflink+0x6d/0x70 net/8021q/vlan_dev.c:766
Read of size 4 at addr ffff8881226e00d0 by task kworker/u4:0/8

CPU: 0 PID: 8 Comm: kworker/u4:0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: netns cleanup_net
Call Trace:
 <TASK>
 __dump_stack+0x21/0x30 lib/dump_stack.c:88
 dump_stack_lvl+0xee/0x150 lib/dump_stack.c:106
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:427 [inline]
 kasan_report+0xf1/0x140 mm/kasan/report.c:444
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report_generic.c:308
 vlan_dev_get_iflink+0x6d/0x70 net/8021q/vlan_dev.c:766
 dev_get_iflink+0x70/0xc0 net/core/dev.c:711
 default_operstate net/core/link_watch.c:41 [inline]
 rfc2863_policy+0x124/0x2b0 net/core/link_watch.c:53
 linkwatch_do_dev+0x3b/0x160 net/core/link_watch.c:160
 linkwatch_forget_dev+0x170/0x180 net/core/link_watch.c:238
 netdev_run_todo+0x2af/0x990 net/core/dev.c:10687
 rtnl_unlock+0xe/0x10 net/core/rtnetlink.c:112
 default_device_exit_batch+0x335/0x390 net/core/dev.c:11684
 ops_exit_list net/core/net_namespace.c:177 [inline]
 cleanup_net+0x602/0xad0 net/core/net_namespace.c:599
 process_one_work+0x6be/0xba0 kernel/workqueue.c:2325
 worker_thread+0xa59/0x1200 kernel/workqueue.c:2472
 kthread+0x411/0x500 kernel/kthread.c:337
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>

Allocated by task 362:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:45 [inline]
 set_alloc_info mm/kasan/common.c:433 [inline]
 ____kasan_kmalloc mm/kasan/common.c:512 [inline]
 __kasan_kmalloc+0xda/0x110 mm/kasan/common.c:521
 kasan_kmalloc include/linux/kasan.h:227 [inline]
 __kmalloc+0x13d/0x2c0 mm/slub.c:4436
 __kmalloc_node include/linux/slab.h:487 [inline]
 kmalloc_node include/linux/slab.h:642 [inline]
 kvmalloc_node+0x206/0x300 mm/util.c:621
 kvmalloc include/linux/mm.h:862 [inline]
 kvzalloc include/linux/mm.h:870 [inline]
 alloc_netdev_mqs+0x8d/0xc90 net/core/dev.c:10900
 rtnl_create_link+0x2ef/0x9d0 net/core/rtnetlink.c:3232
 __rtnl_newlink net/core/rtnetlink.c:3514 [inline]
 rtnl_newlink+0x103f/0x17b0 net/core/rtnetlink.c:3572
 rtnetlink_rcv_msg+0x9e4/0xb90 net/core/rtnetlink.c:5650
 netlink_rcv_skb+0x1e0/0x430 net/netlink/af_netlink.c:2511
 rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:5668
 netlink_unicast_kernel net/netlink/af_netlink.c:1322 [inline]
 netlink_unicast+0x876/0xa40 net/netlink/af_netlink.c:1348
 netlink_sendmsg+0x86a/0xb70 net/netlink/af_netlink.c:1922
 sock_sendmsg_nosec net/socket.c:704 [inline]
 __sock_sendmsg net/socket.c:716 [inline]
 __sys_sendto+0x423/0x580 net/socket.c:2063
 __do_sys_sendto net/socket.c:2075 [inline]
 __se_sys_sendto net/socket.c:2071 [inline]
 __x64_sys_sendto+0xe5/0x100 net/socket.c:2071
 x64_sys_call+0x178/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:45
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

Freed by task 8:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4a/0x70 mm/kasan/common.c:45
 kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:370
 ____kasan_slab_free+0x125/0x160 mm/kasan/common.c:365
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:373
 kasan_slab_free include/linux/kasan.h:193 [inline]
 slab_free_hook mm/slub.c:1728 [inline]
 slab_free_freelist_hook+0xc2/0x190 mm/slub.c:1754
 slab_free mm/slub.c:3526 [inline]
 kfree+0xc4/0x270 mm/slub.c:4588
 kvfree+0x35/0x40 mm/util.c:661
 netdev_freemem+0x3f/0x60 net/core/dev.c:10854
 netdev_release+0x7f/0xb0 net/core/net-sysfs.c:1903
 device_release+0x96/0x1c0 drivers/base/core.c:-1
 kobject_cleanup lib/kobject.c:713 [inline]
 kobject_release lib/kobject.c:744 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x18a/0x270 lib/kobject.c:761
 netdev_run_todo+0x812/0x990 net/core/dev.c:10710
 rtnl_unlock+0xe/0x10 net/core/rtnetlink.c:112
 default_device_exit_batch+0x335/0x390 net/core/dev.c:11684
 ops_exit_list net/core/net_namespace.c:177 [inline]
 cleanup_net+0x602/0xad0 net/core/net_namespace.c:599
 process_one_work+0x6be/0xba0 kernel/workqueue.c:2325
 worker_thread+0xa59/0x1200 kernel/workqueue.c:2472
 kthread+0x411/0x500 kernel/kthread.c:337
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

The buggy address belongs to the object at ffff8881226e0000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 208 bytes inside of
 4096-byte region [ffff8881226e0000, ffff8881226e1000)
The buggy address belongs to the page:
page:ffffea000489b800 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1226e0
head:ffffea000489b800 order:3 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 0000000000000000 dead000000000122 ffff888100043380
raw: 0000000000000000 0000000000040004 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 362, ts 26318180519, free_ts 25163316112
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x192/0x1b0 mm/page_alloc.c:2605
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2611
 get_page_from_freelist+0x2cc5/0x2d50 mm/page_alloc.c:4485
 __alloc_pages+0x18f/0x440 mm/page_alloc.c:5808
 alloc_slab_page mm/slub.c:-1 [inline]
 allocate_slab mm/slub.c:1937 [inline]
 new_slab+0xa1/0x4d0 mm/slub.c:2000
 ___slab_alloc+0x381/0x810 mm/slub.c:3033
 __slab_alloc+0x49/0x90 mm/slub.c:3120
 slab_alloc_node mm/slub.c:3211 [inline]
 slab_alloc mm/slub.c:3255 [inline]
 kmem_cache_alloc_trace+0x146/0x270 mm/slub.c:3272
 kmalloc include/linux/slab.h:619 [inline]
 kzalloc include/linux/slab.h:750 [inline]
 kobject_uevent_env+0x272/0x700 lib/kobject_uevent.c:539
 kobject_uevent+0x1d/0x30 lib/kobject_uevent.c:657
 __kobject_del+0xd7/0x2f0 lib/kobject.c:625
 kobject_cleanup lib/kobject.c:704 [inline]
 kobject_release lib/kobject.c:744 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x1db/0x270 lib/kobject.c:761
 net_rx_queue_update_kobjects+0x40e/0x480 net/core/net-sysfs.c:1124
 netif_set_real_num_rx_queues+0x107/0x1f0 net/core/dev.c:3027
 veth_init_queues+0x116/0x180 drivers/net/veth.c:1613
 veth_newlink+0xab7/0xda0 drivers/net/veth.c:1732
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 free_pages_prepare mm/page_alloc.c:1472 [inline]
 free_pcp_prepare mm/page_alloc.c:1544 [inline]
 free_unref_page_prepare+0x542/0x550 mm/page_alloc.c:3534
 free_unref_page+0xa2/0x550 mm/page_alloc.c:3616
 free_the_page mm/page_alloc.c:805 [inline]
 __free_pages+0x6c/0x100 mm/page_alloc.c:5884
 __vunmap+0x84d/0x9e0 mm/vmalloc.c:2660
 __vfree mm/vmalloc.c:2709 [inline]
 vfree+0x8b/0xc0 mm/vmalloc.c:2740
 kcov_put kernel/kcov.c:417 [inline]
 kcov_close+0x2b/0x50 kernel/kcov.c:519
 __fput+0x20b/0x8b0 fs/file_table.c:311
 ____fput+0x15/0x20 fs/file_table.c:339
 task_work_run+0x127/0x190 kernel/task_work.c:188
 exit_task_work include/linux/task_work.h:33 [inline]
 do_exit+0xa7e/0x27a0 kernel/exit.c:889
 do_group_exit+0x141/0x310 kernel/exit.c:1003
 get_signal+0x66a/0x1480 kernel/signal.c:2907
 arch_do_signal_or_restart+0xc1/0x10f0 arch/x86/kernel/signal.c:867
 handle_signal_work kernel/entry/common.c:154 [inline]
 exit_to_user_mode_loop+0xa7/0xe0 kernel/entry/common.c:178
 exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:214
 __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
 syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:307

Memory state around the buggy address:
 ffff8881226dff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8881226e0000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8881226e0080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                 ^
 ffff8881226e0100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881226e0180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (14):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/10/31 17:39 android13-5.15-lts 1edb21e89ce4 2c50b6a9 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (clean fs)] ci2-android-5-15 KASAN: use-after-free Read in vlan_dev_get_iflink
2025/02/21 16:50 android13-5.15-lts 058abb720bd1 0808a665 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in vlan_dev_get_iflink
2025/10/30 21:58 android13-5.15-lts 1edb21e89ce4 2c50b6a9 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in vlan_dev_get_iflink
2025/03/04 09:13 android13-5.15-lts 7d1f9b5c2ff5 c3901742 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in vlan_dev_get_iflink
2025/02/28 16:24 android13-5.15-lts 7d1f9b5c2ff5 67cf5345 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in vlan_dev_get_iflink
2025/02/26 23:19 android13-5.15-lts 7d1f9b5c2ff5 6a8fcbc4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in vlan_dev_get_iflink
2025/02/21 15:30 android13-5.15-lts 058abb720bd1 0808a665 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in vlan_dev_get_iflink
2025/02/21 12:30 android13-5.15-lts 058abb720bd1 0808a665 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in vlan_dev_get_iflink
2025/02/21 11:34 android13-5.15-lts 058abb720bd1 0808a665 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in vlan_dev_get_iflink
2025/02/21 11:25 android13-5.15-lts 058abb720bd1 0808a665 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in vlan_dev_get_iflink
2025/01/20 12:23 android13-5.15-lts 829d9f138569 f2cb035c .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in vlan_dev_get_iflink
2024/11/23 18:36 android13-5.15-lts 101e665d55a8 68da6d95 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in vlan_dev_get_iflink
2024/10/02 17:06 android13-5.15-lts 8e36931104ac 02f9582a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in vlan_dev_get_iflink
2024/08/13 02:39 android13-5.15-lts 70e1a731d986 7b0f4b46 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in vlan_dev_get_iflink
* Struck through repros no longer work on HEAD.