[moderation] [bridge?] KASAN: slab-use-after-free Read in br_switchdev_fdb_notify

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d0c22de9995b Merge tag 'input-for-v6.15-rc7' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1573e170580000
kernel config: https://syzkaller.appspot.com/x/.config?x=9fd1c9848687d742
dashboard link: https://syzkaller.appspot.com/bug?extid=409edcbf1a71a5afac1e
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
userspace arch: i386
CC: [bri...@lists.linux.dev da...@davemloft.net edum...@google.com ho...@kernel.org ido...@nvidia.com ku...@kernel.org linux-...@vger.kernel.org net...@vger.kernel.org pab...@redhat.com ra...@blackwall.org ro...@nvidia.com]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/877ae05716bc/disk-d0c22de9.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ed6ebfb8cbab/vmlinux-d0c22de9.xz
kernel image: https://storage.googleapis.com/syzbot-assets/18b1fac36f77/bzImage-d0c22de9.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+409edc...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in br_switchdev_fdb_populate net/bridge/br_switchdev.c:138 [inline]
BUG: KASAN: slab-use-after-free in br_switchdev_fdb_notify+0x30b/0x3e0 net/bridge/br_switchdev.c:162
Read of size 8 at addr ffff888035082008 by task kworker/1:5/5890

CPU: 1 UID: 0 PID: 5890 Comm: kworker/1:5 Not tainted 6.15.0-rc7-syzkaller-00152-gd0c22de9995b #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
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:408 [inline]
print_report+0xb4/0x290 mm/kasan/report.c:521
kasan_report+0x118/0x150 mm/kasan/report.c:634
br_switchdev_fdb_populate net/bridge/br_switchdev.c:138 [inline]
br_switchdev_fdb_notify+0x30b/0x3e0 net/bridge/br_switchdev.c:162
fdb_notify+0x89/0x160 net/bridge/br_fdb.c:186
fdb_delete+0xec4/0x1160 net/bridge/br_fdb.c:324
br_fdb_cleanup+0x2aa/0x4d0 net/bridge/br_fdb.c:568
process_one_work kernel/workqueue.c:3238 [inline]
process_scheduled_works+0xadb/0x17a0 kernel/workqueue.c:3319
worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
kthread+0x70e/0x8a0 kernel/kthread.c:464
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>

Allocated by task 5850:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
poison_kmalloc_redzone mm/kasan/common.c:377 [inline]
__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:394
kasan_kmalloc include/linux/kasan.h:260 [inline]
__kmalloc_cache_noprof+0x230/0x3d0 mm/slub.c:4358
kmalloc_noprof include/linux/slab.h:905 [inline]
kzalloc_noprof include/linux/slab.h:1039 [inline]
new_nbp+0x188/0x440 net/bridge/br_if.c:431
br_add_if+0x28e/0xec0 net/bridge/br_if.c:599
do_set_master+0x533/0x6d0 net/core/rtnetlink.c:2946
do_setlink+0xd47/0x40d0 net/core/rtnetlink.c:3159
rtnl_changelink net/core/rtnetlink.c:3769 [inline]
__rtnl_newlink net/core/rtnetlink.c:3928 [inline]
rtnl_newlink+0x160b/0x1c70 net/core/rtnetlink.c:4065
rtnetlink_rcv_msg+0x7cc/0xb70 net/core/rtnetlink.c:6955
netlink_rcv_skb+0x219/0x490 net/netlink/af_netlink.c:2534
netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
netlink_unicast+0x75b/0x8d0 net/netlink/af_netlink.c:1339
netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1883
sock_sendmsg_nosec net/socket.c:712 [inline]
__sock_sendmsg+0x21c/0x270 net/socket.c:727
__sys_sendto+0x3bd/0x520 net/socket.c:2180
__do_compat_sys_socketcall net/compat.c:-1 [inline]
__se_compat_sys_socketcall net/compat.c:423 [inline]
__ia32_compat_sys_socketcall+0x71c/0x9c0 net/compat.c:423
do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
__do_fast_syscall_32+0xb4/0x110 arch/x86/entry/syscall_32.c:306
do_fast_syscall_32+0x34/0x80 arch/x86/entry/syscall_32.c:331
entry_SYSENTER_compat_after_hwframe+0x84/0x8e

Freed by task 23:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:576
poison_slab_object mm/kasan/common.c:247 [inline]
__kasan_slab_free+0x62/0x70 mm/kasan/common.c:264
kasan_slab_free include/linux/kasan.h:233 [inline]
slab_free_hook mm/slub.c:2380 [inline]
slab_free mm/slub.c:4642 [inline]
kfree+0x193/0x440 mm/slub.c:4841
kobject_cleanup lib/kobject.c:689 [inline]
kobject_release lib/kobject.c:720 [inline]
kref_put include/linux/kref.h:65 [inline]
kobject_put+0x22b/0x480 lib/kobject.c:737
rcu_do_batch kernel/rcu/tree.c:2568 [inline]
rcu_core+0xca8/0x1710 kernel/rcu/tree.c:2824
handle_softirqs+0x286/0x870 kernel/softirq.c:579
run_ksoftirqd+0x9b/0x100 kernel/softirq.c:968
smpboot_thread_fn+0x542/0xa60 kernel/smpboot.c:164
kthread+0x70e/0x8a0 kernel/kthread.c:464
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Last potentially related work creation:
kasan_save_stack+0x3e/0x60 mm/kasan/common.c:47
kasan_record_aux_stack+0xbc/0xd0 mm/kasan/generic.c:548
__call_rcu_common kernel/rcu/tree.c:3082 [inline]
call_rcu+0x142/0x990 kernel/rcu/tree.c:3202
br_del_if+0x146/0x320 net/bridge/br_if.c:739
do_set_master+0x30f/0x6d0 net/core/rtnetlink.c:2930
do_setlink+0xd47/0x40d0 net/core/rtnetlink.c:3159
rtnl_group_changelink net/core/rtnetlink.c:3783 [inline]
__rtnl_newlink net/core/rtnetlink.c:3937 [inline]
rtnl_newlink+0x149f/0x1c70 net/core/rtnetlink.c:4065
rtnetlink_rcv_msg+0x7cc/0xb70 net/core/rtnetlink.c:6955
netlink_rcv_skb+0x219/0x490 net/netlink/af_netlink.c:2534
netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
netlink_unicast+0x75b/0x8d0 net/netlink/af_netlink.c:1339
netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1883
sock_sendmsg_nosec net/socket.c:712 [inline]
__sock_sendmsg+0x21c/0x270 net/socket.c:727
____sys_sendmsg+0x505/0x830 net/socket.c:2566
___sys_sendmsg+0x21f/0x2a0 net/socket.c:2620
__sys_sendmsg+0x164/0x220 net/socket.c:2652
do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
__do_fast_syscall_32+0xb4/0x110 arch/x86/entry/syscall_32.c:306
do_fast_syscall_32+0x34/0x80 arch/x86/entry/syscall_32.c:331
entry_SYSENTER_compat_after_hwframe+0x84/0x8e

The buggy address belongs to the object at ffff888035082000
which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 8 bytes inside of
freed 1024-byte region [ffff888035082000, ffff888035082400)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x35080
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801a041dc0 ffffea0001f6d800 dead000000000002
raw: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801a041dc0 ffffea0001f6d800 dead000000000002
head: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea0000d42001 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 5851, tgid 5851 (syz-executor), ts 79590784104, free_ts 79575620413
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x1d8/0x230 mm/page_alloc.c:1714
prep_new_page mm/page_alloc.c:1722 [inline]
get_page_from_freelist+0x21ce/0x22b0 mm/page_alloc.c:3684
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:4966
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2301
alloc_slab_page mm/slub.c:2450 [inline]
allocate_slab+0x8a/0x3b0 mm/slub.c:2618
new_slab mm/slub.c:2672 [inline]
___slab_alloc+0xbfc/0x1480 mm/slub.c:3858
__slab_alloc mm/slub.c:3948 [inline]
__slab_alloc_node mm/slub.c:4023 [inline]
slab_alloc_node mm/slub.c:4184 [inline]
__kmalloc_cache_noprof+0x296/0x3d0 mm/slub.c:4353
kmalloc_noprof include/linux/slab.h:905 [inline]
kzalloc_noprof include/linux/slab.h:1039 [inline]
batadv_hardif_add_interface net/batman-adv/hard-interface.c:884 [inline]
batadv_hard_if_event+0x11b7/0x1a50 net/batman-adv/hard-interface.c:968
notifier_call_chain+0x1b6/0x3e0 kernel/notifier.c:85
call_netdevice_notifiers_extack net/core/dev.c:2214 [inline]
call_netdevice_notifiers net/core/dev.c:2228 [inline]
register_netdevice+0x1608/0x1af0 net/core/dev.c:11037
veth_newlink+0x42f/0xa50 drivers/net/veth.c:1818
rtnl_newlink_create+0x308/0xaf0 net/core/rtnetlink.c:3833
__rtnl_newlink net/core/rtnetlink.c:3950 [inline]
rtnl_newlink+0x16d6/0x1c70 net/core/rtnetlink.c:4065
rtnetlink_rcv_msg+0x7cc/0xb70 net/core/rtnetlink.c:6955
netlink_rcv_skb+0x219/0x490 net/netlink/af_netlink.c:2534
netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
netlink_unicast+0x75b/0x8d0 net/netlink/af_netlink.c:1339
page last free pid 5850 tgid 5850 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1258 [inline]
__free_frozen_pages+0xb0e/0xcd0 mm/page_alloc.c:2721
__slab_free+0x326/0x400 mm/slub.c:4553
qlink_free mm/kasan/quarantine.c:163 [inline]
qlist_free_all+0x9a/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:329
kasan_slab_alloc include/linux/kasan.h:250 [inline]
slab_post_alloc_hook mm/slub.c:4147 [inline]
slab_alloc_node mm/slub.c:4196 [inline]
__kmalloc_cache_noprof+0x1be/0x3d0 mm/slub.c:4353
kmalloc_noprof include/linux/slab.h:905 [inline]
kzalloc_noprof include/linux/slab.h:1039 [inline]
kset_create lib/kobject.c:965 [inline]
kset_create_and_add+0x5a/0x170 lib/kobject.c:1008
register_queue_kobjects net/core/net-sysfs.c:2085 [inline]
netdev_register_kobject+0x180/0x2f0 net/core/net-sysfs.c:2340
register_netdevice+0x126c/0x1af0 net/core/dev.c:10999
veth_newlink+0x42f/0xa50 drivers/net/veth.c:1818
rtnl_newlink_create+0x308/0xaf0 net/core/rtnetlink.c:3833
__rtnl_newlink net/core/rtnetlink.c:3950 [inline]
rtnl_newlink+0x16d6/0x1c70 net/core/rtnetlink.c:4065
rtnetlink_rcv_msg+0x7cc/0xb70 net/core/rtnetlink.c:6955
netlink_rcv_skb+0x219/0x490 net/netlink/af_netlink.c:2534
netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
netlink_unicast+0x75b/0x8d0 net/netlink/af_netlink.c:1339
netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1883

Memory state around the buggy address:
ffff888035081f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888035081f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888035082000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888035082080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888035082100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.