[syzbot] [bridge?] KASAN: slab-use-after-free Read in br_multicast_add_router

[syzbot <syzbot+7bfa4b72c6a5da128d32@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    82cbd06f327f net: enetc: fix the netc-lib driver build dep..
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=163549d4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=73696606574e3967
dashboard link: https://syzkaller.appspot.com/bug?extid=7bfa4b72c6a5da128d32
compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/7bcff4a03866/disk-82cbd06f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/80e0c2155db8/vmlinux-82cbd06f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e766bd001fb5/bzImage-82cbd06f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7bfa4b72c6a5da128d32@syzkaller.appspotmail.com

netlink: 'syz.1.1059': attribute type 25 has an invalid length.
==================================================================
BUG: KASAN: slab-use-after-free in br_multicast_rport_from_node net/bridge/br_multicast.c:3298 [inline]
BUG: KASAN: slab-use-after-free in br_multicast_get_rport_slot net/bridge/br_multicast.c:3312 [inline]
BUG: KASAN: slab-use-after-free in br_multicast_add_router+0x15e/0x520 net/bridge/br_multicast.c:3350
Read of size 8 at addr ffff8880285f11b0 by task syz.1.1059/9405

CPU: 0 UID: 0 PID: 9405 Comm: syz.1.1059 Not tainted 6.15.0-syzkaller-12425-g82cbd06f327f #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:408 [inline]
 print_report+0xd2/0x2b0 mm/kasan/report.c:521
 kasan_report+0x118/0x150 mm/kasan/report.c:634
 br_multicast_rport_from_node net/bridge/br_multicast.c:3298 [inline]
 br_multicast_get_rport_slot net/bridge/br_multicast.c:3312 [inline]
 br_multicast_add_router+0x15e/0x520 net/bridge/br_multicast.c:3350
 br_multicast_mark_router+0x3fa/0x5d0 net/bridge/br_multicast.c:3416
 br_ip4_multicast_mark_router net/bridge/br_multicast.c:3431 [inline]
 br_multicast_set_port_router+0x3cf/0xc50 net/bridge/br_multicast.c:4569
 br_setport+0xeab/0x1670 net/bridge/br_netlink.c:1027
 br_setlink+0x4d5/0x800 net/bridge/br_netlink.c:1118
 rtnl_bridge_setlink+0x5b2/0x7d0 net/core/rtnetlink.c:5520
 rtnetlink_rcv_msg+0x779/0xb70 net/core/rtnetlink.c:6953
 netlink_rcv_skb+0x205/0x470 net/netlink/af_netlink.c:2534
 netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
 netlink_unicast+0x758/0x8d0 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 net/socket.c:2652 [inline]
 __do_sys_sendmsg net/socket.c:2657 [inline]
 __se_sys_sendmsg net/socket.c:2655 [inline]
 __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2655
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f4e4158e929
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:00007f4e424d3038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f4e417b5fa0 RCX: 00007f4e4158e929
RDX: 0000000000000000 RSI: 0000200000000000 RDI: 0000000000000003
RBP: 00007f4e41610b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f4e417b5fa0 R15: 00007fffe0e7f318
 </TASK>

Allocated by task 5847:
 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:4359
 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+0xcf0/0x41c0 net/core/rtnetlink.c:3148
 rtnl_changelink net/core/rtnetlink.c:3759 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3918 [inline]
 rtnl_newlink+0x160b/0x1c70 net/core/rtnetlink.c:4055
 rtnetlink_rcv_msg+0x7cf/0xb70 net/core/rtnetlink.c:6944
 netlink_rcv_skb+0x205/0x470 net/netlink/af_netlink.c:2534
 netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
 netlink_unicast+0x758/0x8d0 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_sys_sendto net/socket.c:2187 [inline]
 __se_sys_sendto net/socket.c:2183 [inline]
 __x64_sys_sendto+0xde/0x100 net/socket.c:2183
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

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:2381 [inline]
 slab_free mm/slub.c:4643 [inline]
 kfree+0x18e/0x440 mm/slub.c:4842
 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:2576 [inline]
 rcu_core+0xca5/0x1710 kernel/rcu/tree.c:2832
 handle_softirqs+0x286/0x870 kernel/softirq.c:579
 run_ksoftirqd+0x9b/0x100 kernel/softirq.c:968
 smpboot_thread_fn+0x53f/0xa60 kernel/smpboot.c:164
 kthread+0x70e/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148
 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+0xbd/0xd0 mm/kasan/generic.c:548
 __call_rcu_common kernel/rcu/tree.c:3090 [inline]
 call_rcu+0x142/0x990 kernel/rcu/tree.c:3210
 br_del_if+0x146/0x320 net/bridge/br_if.c:739
 do_set_master+0x30f/0x6d0 net/core/rtnetlink.c:2930
 do_setlink+0xcf0/0x41c0 net/core/rtnetlink.c:3148
 rtnl_changelink net/core/rtnetlink.c:3759 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3918 [inline]
 rtnl_newlink+0x160b/0x1c70 net/core/rtnetlink.c:4055
 rtnetlink_rcv_msg+0x7cf/0xb70 net/core/rtnetlink.c:6944
 netlink_rcv_skb+0x205/0x470 net/netlink/af_netlink.c:2534
 netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
 netlink_unicast+0x758/0x8d0 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 net/socket.c:2652 [inline]
 __do_sys_sendmsg net/socket.c:2657 [inline]
 __se_sys_sendmsg net/socket.c:2655 [inline]
 __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2655
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff8880285f1000
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 432 bytes inside of
 freed 1024-byte region [ffff8880285f1000, ffff8880285f1400)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x285f0
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801a441dc0 0000000000000000 dead000000000001
raw: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801a441dc0 0000000000000000 dead000000000001
head: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea0000a17c01 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 0x252800(GFP_NOWAIT|__GFP_NORETRY|__GFP_COMP|__GFP_THISNODE), pid 151, tgid 151 (kworker/u8:5), ts 13293406822, free_ts 0
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1704
 prep_new_page mm/page_alloc.c:1712 [inline]
 get_page_from_freelist+0x21e4/0x22c0 mm/page_alloc.c:3669
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:4959
 alloc_slab_page mm/slub.c:2453 [inline]
 allocate_slab+0x65/0x3b0 mm/slub.c:2619
 new_slab mm/slub.c:2673 [inline]
 ___slab_alloc+0xbfc/0x1480 mm/slub.c:3859
 __slab_alloc mm/slub.c:3949 [inline]
 __slab_alloc_node mm/slub.c:4024 [inline]
 slab_alloc_node mm/slub.c:4185 [inline]
 __do_kmalloc_node mm/slub.c:4327 [inline]
 __kmalloc_node_noprof+0x2fd/0x4e0 mm/slub.c:4334
 kmalloc_node_noprof include/linux/slab.h:932 [inline]
 blk_alloc_flush_queue+0xe2/0x230 block/blk-flush.c:490
 blk_mq_alloc_hctx block/blk-mq.c:4037 [inline]
 blk_mq_alloc_and_init_hctx+0x679/0xd60 block/blk-mq.c:4500
 __blk_mq_realloc_hw_ctxs+0x169/0x400 block/blk-mq.c:4531
 blk_mq_realloc_hw_ctxs block/blk-mq.c:4558 [inline]
 blk_mq_init_allocated_queue+0x400/0x1490 block/blk-mq.c:4590
 blk_mq_alloc_queue+0x197/0x290 block/blk-mq.c:4400
 scsi_alloc_sdev+0x76d/0xb50 drivers/scsi/scsi_scan.c:339
 scsi_probe_and_add_lun+0x1cb/0x4520 drivers/scsi/scsi_scan.c:1210
 __scsi_scan_target+0x1dd/0xd10 drivers/scsi/scsi_scan.c:1775
 scsi_scan_channel drivers/scsi/scsi_scan.c:1863 [inline]
 scsi_scan_host_selected+0x372/0x690 drivers/scsi/scsi_scan.c:1892
 do_scsi_scan_host drivers/scsi/scsi_scan.c:2031 [inline]
 do_scan_async+0x124/0x760 drivers/scsi/scsi_scan.c:2041
page_owner free stack trace missing

Memory state around the buggy address:
 ffff8880285f1080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880285f1100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8880285f1180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                     ^
 ffff8880285f1200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880285f1280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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