[v6.1] KASAN: use-after-free Read in br_switchdev_fdb_notify

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f6e38ae624cf Linux 6.1.158
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1763d192580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7eb38bd5021fec61
dashboard link: https://syzkaller.appspot.com/bug?extid=40ee65725b8d520813cb
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2b7003e2661d/disk-f6e38ae6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0696cea8d016/vmlinux-f6e38ae6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6b7a89e636d7/bzImage-f6e38ae6.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+40ee65...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in br_switchdev_fdb_populate net/bridge/br_switchdev.c:142 [inline]
BUG: KASAN: use-after-free in br_switchdev_fdb_notify+0x2ad/0x380 net/bridge/br_switchdev.c:163
Read of size 8 at addr ffff8880575f5808 by task kworker/1:3/4256

CPU: 1 PID: 4256 Comm: kworker/1:3 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: events_long br_fdb_cleanup
Call Trace:
<TASK>
dump_stack_lvl+0x168/0x22e lib/dump_stack.c:106
print_address_description mm/kasan/report.c:316 [inline]
print_report+0xa8/0x210 mm/kasan/report.c:420
kasan_report+0x10b/0x140 mm/kasan/report.c:524
br_switchdev_fdb_populate net/bridge/br_switchdev.c:142 [inline]
br_switchdev_fdb_notify+0x2ad/0x380 net/bridge/br_switchdev.c:163
fdb_notify+0x89/0x160 net/bridge/br_fdb.c:189
fdb_delete+0xd52/0x10f0 net/bridge/br_fdb.c:325
br_fdb_cleanup+0x2a3/0x4c0 net/bridge/br_fdb.c:550
process_one_work+0x898/0x1160 kernel/workqueue.c:2292
worker_thread+0xaa2/0x1250 kernel/workqueue.c:2439
kthread+0x29d/0x330 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
</TASK>

Allocated by task 0:
kasan_save_stack mm/kasan/common.c:45 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:52
____kasan_kmalloc mm/kasan/common.c:374 [inline]
__kasan_kmalloc+0x8e/0xa0 mm/kasan/common.c:383
kasan_kmalloc include/linux/kasan.h:211 [inline]
__do_kmalloc_node mm/slab_common.c:936 [inline]
__kmalloc_node_track_caller+0xae/0x230 mm/slab_common.c:956
kmalloc_reserve net/core/skbuff.c:446 [inline]
__alloc_skb+0x22a/0x7e0 net/core/skbuff.c:515
alloc_skb include/linux/skbuff.h:1271 [inline]
__tcp_send_ack+0x9d/0x5a0 net/ipv4/tcp_output.c:4033
tcp_ack_snd_check net/ipv4/tcp_input.c:5672 [inline]
tcp_rcv_established+0xeb6/0x1d30 net/ipv4/tcp_input.c:6116
tcp_v4_do_rcv+0x48d/0xb00 net/ipv4/tcp_ipv4.c:1683
tcp_v4_rcv+0x2789/0x2e30 net/ipv4/tcp_ipv4.c:2114
ip_protocol_deliver_rcu+0x3ad/0x780 net/ipv4/ip_input.c:205
ip_local_deliver_finish+0x2c7/0x510 net/ipv4/ip_input.c:233
NF_HOOK+0x2ff/0x390 include/linux/netfilter.h:302
dst_input include/net/dst.h:463 [inline]
ip_sublist_rcv_finish net/ipv4/ip_input.c:580 [inline]
ip_list_rcv_finish net/ipv4/ip_input.c:631 [inline]
ip_sublist_rcv+0xa30/0xd10 net/ipv4/ip_input.c:639
ip_list_rcv+0x3df/0x430 net/ipv4/ip_input.c:674
__netif_receive_skb_list_ptype net/core/dev.c:5624 [inline]
__netif_receive_skb_list_core+0x574/0x740 net/core/dev.c:5672
__netif_receive_skb_list net/core/dev.c:5724 [inline]
netif_receive_skb_list_internal+0x90f/0xc50 net/core/dev.c:5815
gro_normal_list include/net/gro.h:433 [inline]
napi_complete_done+0x37d/0x830 net/core/dev.c:6156
virtqueue_napi_complete drivers/net/virtio_net.c:403 [inline]
virtnet_poll+0x991/0x1150 drivers/net/virtio_net.c:1717
__napi_poll+0xc0/0x460 net/core/dev.c:6590
napi_poll net/core/dev.c:6657 [inline]
net_rx_action+0x5b1/0xad0 net/core/dev.c:6771
handle_softirqs+0x2a1/0x920 kernel/softirq.c:596
__do_softirq kernel/softirq.c:630 [inline]
invoke_softirq kernel/softirq.c:470 [inline]
__irq_exit_rcu+0x12f/0x220 kernel/softirq.c:679
irq_exit_rcu+0x5/0x20 kernel/softirq.c:691
common_interrupt+0xb5/0xd0 arch/x86/kernel/irq.c:242
asm_common_interrupt+0x22/0x40 arch/x86/include/asm/idtentry.h:682

Freed by task 32:
kasan_save_stack mm/kasan/common.c:45 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:52
kasan_save_free_info+0x2d/0x50 mm/kasan/generic.c:516
____kasan_slab_free+0x126/0x1e0 mm/kasan/common.c:236
kasan_slab_free include/linux/kasan.h:177 [inline]
slab_free_hook mm/slub.c:1729 [inline]
slab_free_freelist_hook+0x131/0x1a0 mm/slub.c:1755
slab_free mm/slub.c:3687 [inline]
__kmem_cache_free+0xb6/0x1f0 mm/slub.c:3700
skb_free_head net/core/skbuff.c:762 [inline]
skb_release_data+0x5db/0x7c0 net/core/skbuff.c:791
skb_release_all net/core/skbuff.c:856 [inline]
napi_consume_skb+0x12f/0x1d0 net/core/skbuff.c:1113
free_old_xmit_skbs+0x111/0x2a0 drivers/net/virtio_net.c:1639
virtnet_poll_tx+0x20f/0x520 drivers/net/virtio_net.c:1811
__napi_poll+0xc0/0x460 net/core/dev.c:6590
napi_poll net/core/dev.c:6657 [inline]
net_rx_action+0x5b1/0xad0 net/core/dev.c:6771
handle_softirqs+0x2a1/0x920 kernel/softirq.c:596
__do_softirq kernel/softirq.c:630 [inline]
invoke_softirq kernel/softirq.c:470 [inline]
__irq_exit_rcu+0x12f/0x220 kernel/softirq.c:679
irq_exit_rcu+0x5/0x20 kernel/softirq.c:691
common_interrupt+0xb5/0xd0 arch/x86/kernel/irq.c:242
asm_common_interrupt+0x22/0x40 arch/x86/include/asm/idtentry.h:682

Last potentially related work creation:
kasan_save_stack+0x3a/0x60 mm/kasan/common.c:45
__kasan_record_aux_stack+0xb2/0xc0 mm/kasan/generic.c:486
call_rcu+0x154/0x980 kernel/rcu/tree.c:2849
br_del_if+0x15d/0x330 net/bridge/br_if.c:739
do_set_master net/core/rtnetlink.c:2616 [inline]
do_setlink+0xe3c/0x3c40 net/core/rtnetlink.c:2840
rtnl_group_changelink net/core/rtnetlink.c:3361 [inline]
__rtnl_newlink net/core/rtnetlink.c:3618 [inline]
rtnl_newlink+0x10a3/0x1ff0 net/core/rtnetlink.c:3655
rtnetlink_rcv_msg+0x79b/0xed0 net/core/rtnetlink.c:6150
netlink_rcv_skb+0x1de/0x420 net/netlink/af_netlink.c:2511
netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
netlink_unicast+0x74d/0x8d0 net/netlink/af_netlink.c:1344
netlink_sendmsg+0x89e/0xbc0 net/netlink/af_netlink.c:1872
sock_sendmsg_nosec net/socket.c:718 [inline]
__sock_sendmsg net/socket.c:730 [inline]
____sys_sendmsg+0x59b/0x970 net/socket.c:2519
___sys_sendmsg+0x21c/0x290 net/socket.c:2573
__sys_sendmsg net/socket.c:2602 [inline]
__do_sys_sendmsg net/socket.c:2611 [inline]
__se_sys_sendmsg+0x19e/0x270 net/socket.c:2609
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff8880575f5800
which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 8 bytes inside of
1024-byte region [ffff8880575f5800, ffff8880575f5c00)

The buggy address belongs to the physical page:
page:ffffea00015d7c00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x575f0
head:ffffea00015d7c00 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 dead000000000100 dead000000000122 ffff888017441dc0
raw: 0000000000000000 0000000000100010 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 0x52a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 4273, tgid 4273 (syz-executor), ts 79282216194, free_ts 22688754025
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook+0x173/0x1a0 mm/page_alloc.c:2532
prep_new_page mm/page_alloc.c:2539 [inline]
get_page_from_freelist+0x1a26/0x1ac0 mm/page_alloc.c:4328
__alloc_pages+0x1df/0x4e0 mm/page_alloc.c:5614
alloc_slab_page+0x5d/0x160 mm/slub.c:1799
allocate_slab mm/slub.c:1944 [inline]
new_slab+0x87/0x2c0 mm/slub.c:1997
___slab_alloc+0xbc6/0x1230 mm/slub.c:3154
__slab_alloc mm/slub.c:3240 [inline]
slab_alloc_node mm/slub.c:3325 [inline]
__kmem_cache_alloc_node+0x1a0/0x260 mm/slub.c:3398
__do_kmalloc_node mm/slab_common.c:935 [inline]
__kmalloc+0xa0/0x240 mm/slab_common.c:949
kmalloc_array include/linux/slab.h:615 [inline]
batadv_hash_new+0x77/0x290 net/batman-adv/hash.c:52
batadv_bla_init+0x44b/0x6f0 net/batman-adv/bridge_loop_avoidance.c:1563
batadv_mesh_init+0x3d8/0x700 net/batman-adv/main.c:211
batadv_softif_init_late+0x9b6/0xe50 net/batman-adv/soft-interface.c:810
register_netdevice+0x65b/0x1aa0 net/core/dev.c:10130
rtnl_newlink_create net/core/rtnetlink.c:3422 [inline]
__rtnl_newlink net/core/rtnetlink.c:3642 [inline]
rtnl_newlink+0x14c4/0x1ff0 net/core/rtnetlink.c:3655
rtnetlink_rcv_msg+0x79b/0xed0 net/core/rtnetlink.c:6150
netlink_rcv_skb+0x1de/0x420 net/netlink/af_netlink.c:2511
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1459 [inline]
free_pcp_prepare mm/page_alloc.c:1509 [inline]
free_unref_page_prepare+0x8b4/0x9a0 mm/page_alloc.c:3384
free_unref_page+0x2e/0x3f0 mm/page_alloc.c:3479
free_contig_range+0x9d/0x150 mm/page_alloc.c:9574
destroy_args+0x100/0xa31 mm/debug_vm_pgtable.c:1031
debug_vm_pgtable+0x32a/0x37e mm/debug_vm_pgtable.c:1359
do_one_initcall+0x214/0x7a0 init/main.c:1310
do_initcall_level+0x137/0x1e4 init/main.c:1383
do_initcalls+0x4b/0x8a init/main.c:1399
kernel_init_freeable+0x3fa/0x5ac init/main.c:1638
kernel_init+0x19/0x1b0 init/main.c:1526
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

Memory state around the buggy address:
ffff8880575f5700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880575f5780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8880575f5800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880575f5880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880575f5900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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