KASAN: slab-use-after-free Read in br_switchdev_fdb_notify (2)

Status: fixed on 2026/01/22 13:50
Subsystems: bridge
[Documentation on labels]
Reported-by: syzbot+8a7f78e2f99977bb8765@syzkaller.appspotmail.com
Fix commit: 8dca36978aa8 net: bridge: fix use-after-free due to MST port state bypass
First crash: 291d, last: 271d
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [bridge?] KASAN: slab-use-after-free Read in br_switchdev_fdb_notify (2) 0 (2) 2026/01/20 14:36
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: slab-use-after-free Read in br_switchdev_fdb_notify bridge 19 2 415d 422d 0/29 auto-obsoleted due to no activity on 2025/09/02 15:50
upstream general protection fault in br_switchdev_fdb_notify bridge 2 C error 82 1813d 1818d 20/29 fixed on 2021/11/10 00:50
linux-6.1 KASAN: use-after-free Read in br_switchdev_fdb_notify 19 1 232d 232d 0/3 auto-obsoleted due to no activity on 2026/03/14 12:44

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in br_switchdev_fdb_populate net/bridge/br_switchdev.c:141 [inline]
BUG: KASAN: slab-use-after-free in br_switchdev_fdb_notify+0x30b/0x3e0 net/bridge/br_switchdev.c:165
Read of size 8 at addr ffff888032ecd808 by task kworker/1:16/6949

CPU: 1 UID: 0 PID: 6949 Comm: kworker/1:16 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: events_long br_fdb_cleanup
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xca/0x240 mm/kasan/report.c:482
 kasan_report+0x118/0x150 mm/kasan/report.c:595
 br_switchdev_fdb_populate net/bridge/br_switchdev.c:141 [inline]
 br_switchdev_fdb_notify+0x30b/0x3e0 net/bridge/br_switchdev.c:165
 fdb_notify+0x89/0x160 net/bridge/br_fdb.c:186
 fdb_delete+0xdcf/0x1060 net/bridge/br_fdb.c:324
 br_fdb_cleanup+0x2aa/0x4d0 net/bridge/br_fdb.c:574
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

Allocated by task 6412:
 kasan_save_stack mm/kasan/common.c:56 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
 poison_kmalloc_redzone mm/kasan/common.c:400 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:417
 kasan_kmalloc include/linux/kasan.h:262 [inline]
 __do_kmalloc_node mm/slub.c:5634 [inline]
 __kmalloc_noprof+0x411/0x7f0 mm/slub.c:5646
 kmalloc_noprof include/linux/slab.h:961 [inline]
 kzalloc_noprof include/linux/slab.h:1094 [inline]
 ieee802_11_parse_elems_full+0x152/0x2ab0 net/mac80211/parse.c:1011
 ieee802_11_parse_elems_crc net/mac80211/ieee80211_i.h:2470 [inline]
 ieee802_11_parse_elems net/mac80211/ieee80211_i.h:2477 [inline]
 ieee80211_rx_mgmt_probe_beacon net/mac80211/ibss.c:1569 [inline]
 ieee80211_ibss_rx_queued_mgmt+0x47a/0x2af0 net/mac80211/ibss.c:1600
 ieee80211_iface_process_skb net/mac80211/iface.c:1694 [inline]
 ieee80211_iface_work+0x85f/0x12d0 net/mac80211/iface.c:1748
 cfg80211_wiphy_work+0x2bb/0x470 net/wireless/core.c:435
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Freed by task 6412:
 kasan_save_stack mm/kasan/common.c:56 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
 __kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:587
 kasan_save_free_info mm/kasan/kasan.h:406 [inline]
 poison_slab_object mm/kasan/common.c:252 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:284
 kasan_slab_free include/linux/kasan.h:234 [inline]
 slab_free_hook mm/slub.c:2530 [inline]
 slab_free mm/slub.c:6619 [inline]
 kfree+0x19a/0x6d0 mm/slub.c:6826
 ieee80211_rx_mgmt_probe_beacon net/mac80211/ibss.c:1574 [inline]
 ieee80211_ibss_rx_queued_mgmt+0x1207/0x2af0 net/mac80211/ibss.c:1600
 ieee80211_iface_process_skb net/mac80211/iface.c:1694 [inline]
 ieee80211_iface_work+0x85f/0x12d0 net/mac80211/iface.c:1748
 cfg80211_wiphy_work+0x2bb/0x470 net/wireless/core.c:435
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The buggy address belongs to the object at ffff888032ecd800
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 8 bytes inside of
 freed 1024-byte region [ffff888032ecd800, ffff888032ecdc00)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x32ec8
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
ksm flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801a026dc0 ffffea00014fac00 dead000000000003
raw: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801a026dc0 ffffea00014fac00 dead000000000003
head: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea0000cbb201 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0x52820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 5828, tgid 5828 (syz-executor), ts 74336496992, free_ts 74334892510
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1850
 prep_new_page mm/page_alloc.c:1858 [inline]
 get_page_from_freelist+0x2365/0x2440 mm/page_alloc.c:3884
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5183
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
 alloc_slab_page mm/slub.c:3046 [inline]
 allocate_slab+0x96/0x3a0 mm/slub.c:3219
 new_slab mm/slub.c:3273 [inline]
 ___slab_alloc+0xe94/0x18a0 mm/slub.c:4643
 __slab_alloc+0x65/0x100 mm/slub.c:4762
 __slab_alloc_node mm/slub.c:4838 [inline]
 slab_alloc_node mm/slub.c:5260 [inline]
 __kmalloc_cache_noprof+0x411/0x6f0 mm/slub.c:5750
 kmalloc_noprof include/linux/slab.h:957 [inline]
 kzalloc_noprof include/linux/slab.h:1094 [inline]
 batadv_hardif_add_interface net/batman-adv/hard-interface.c:874 [inline]
 batadv_hard_if_event+0xe9a/0x1730 net/batman-adv/hard-interface.c:958
 notifier_call_chain+0x1b6/0x3e0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
 call_netdevice_notifiers net/core/dev.c:2281 [inline]
 register_netdevice+0x1608/0x1ae0 net/core/dev.c:11332
 veth_newlink+0x5d4/0xa60 drivers/net/veth.c:1884
 rtnl_newlink_create+0x310/0xb00 net/core/rtnetlink.c:3833
 __rtnl_newlink net/core/rtnetlink.c:3950 [inline]
 rtnl_newlink+0x16e4/0x1c80 net/core/rtnetlink.c:4065
 rtnetlink_rcv_msg+0x7cf/0xb70 net/core/rtnetlink.c:6951
 netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2552
page last free pid 5828 tgid 5828 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1394 [inline]
 __free_frozen_pages+0xbc4/0xd30 mm/page_alloc.c:2906
 __slab_free+0x2e7/0x390 mm/slub.c:5954
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x97/0x140 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:352
 kasan_slab_alloc include/linux/kasan.h:252 [inline]
 slab_post_alloc_hook mm/slub.c:4962 [inline]
 slab_alloc_node mm/slub.c:5272 [inline]
 __kmalloc_cache_noprof+0x36f/0x6f0 mm/slub.c:5750
 kmalloc_noprof include/linux/slab.h:957 [inline]
 kzalloc_noprof include/linux/slab.h:1094 [inline]
 ref_tracker_alloc+0x133/0x460 lib/ref_tracker.c:271
 __netdev_tracker_alloc include/linux/netdevice.h:4375 [inline]
 netdev_hold include/linux/netdevice.h:4404 [inline]
 rx_queue_add_kobject net/core/net-sysfs.c:1257 [inline]
 net_rx_queue_update_kobjects+0x1a6/0x740 net/core/net-sysfs.c:1322
 register_queue_kobjects net/core/net-sysfs.c:2114 [inline]
 netdev_register_kobject+0x21f/0x310 net/core/net-sysfs.c:2362
 register_netdevice+0x126c/0x1ae0 net/core/dev.c:11294
 veth_newlink+0x5d4/0xa60 drivers/net/veth.c:1884
 rtnl_newlink_create+0x310/0xb00 net/core/rtnetlink.c:3833
 __rtnl_newlink net/core/rtnetlink.c:3950 [inline]
 rtnl_newlink+0x16e4/0x1c80 net/core/rtnetlink.c:4065
 rtnetlink_rcv_msg+0x7cf/0xb70 net/core/rtnetlink.c:6951
 netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2552
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1346

Memory state around the buggy address:
 ffff888032ecd700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888032ecd780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888032ecd800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff888032ecd880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888032ecd900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/10/27 05:08 net 84a905290cb4 c0460fcd .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce KASAN: slab-use-after-free Read in br_switchdev_fdb_notify
2025/10/06 16:09 net 1b54b0756f05 91305dbe .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce KASAN: slab-use-after-free Read in br_switchdev_fdb_notify
2025/10/25 15:23 net-next bfe62db5422b c0460fcd .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce KASAN: slab-use-after-free Read in br_switchdev_fdb_notify
2025/10/17 12:06 net-next 7e0d4c111369 7adf5298 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce KASAN: slab-use-after-free Read in br_switchdev_fdb_notify
* Struck through repros no longer work on HEAD.