[v5.15] KASAN: use-after-free Read in l2cap_sock_new_connection_cb (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cc5ec8769306 Linux 5.15.196
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=15849e92580000
kernel config: https://syzkaller.appspot.com/x/.config?x=e1bb6d24ef2164eb
dashboard link: https://syzkaller.appspot.com/bug?extid=424eb096397600e92a91
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=124d657c580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c71c660545b2/disk-cc5ec876.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/4f011826cca6/vmlinux-cc5ec876.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8ccd1a2c3f8c/bzImage-cc5ec876.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+424eb0...@syzkaller.appspotmail.com

ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
</TASK>
kobject_add_internal failed for hci1:201 with -EEXIST, don't try to register things with the same name in the same directory.
Bluetooth: hci1: failed to register connection device
==================================================================
BUG: KASAN: use-after-free in l2cap_sock_new_connection_cb+0x125/0x1c0 net/bluetooth/l2cap_sock.c:1494
Read of size 8 at addr ffff88807bdc0550 by task kworker/u5:0/146

CPU: 1 PID: 146 Comm: kworker/u5:0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: hci1 hci_rx_work
Call Trace:
<TASK>
dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
print_address_description+0x60/0x2d0 mm/kasan/report.c:248
__kasan_report mm/kasan/report.c:434 [inline]
kasan_report+0xdf/0x130 mm/kasan/report.c:451
l2cap_sock_new_connection_cb+0x125/0x1c0 net/bluetooth/l2cap_sock.c:1494
l2cap_connect_cfm+0x35d/0x10d0 net/bluetooth/l2cap_core.c:8303
hci_connect_cfm include/net/bluetooth/hci_core.h:1505 [inline]
le_conn_complete_evt+0xdaf/0x1590 net/bluetooth/hci_event.c:5439
hci_le_conn_complete_evt net/bluetooth/hci_event.c:5464 [inline]
hci_le_meta_evt+0x289/0x3b80 net/bluetooth/hci_event.c:6186
hci_event_packet+0xe05/0x12f0 net/bluetooth/hci_event.c:6535
hci_rx_work+0x255/0xa10 net/bluetooth/hci_core.c:5160
process_one_work+0x863/0x1000 kernel/workqueue.c:2310
worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
kthread+0x436/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
</TASK>

Allocated by task 146:
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track mm/kasan/common.c:46 [inline]
set_alloc_info mm/kasan/common.c:434 [inline]
____kasan_kmalloc mm/kasan/common.c:513 [inline]
__kasan_kmalloc+0xb5/0xf0 mm/kasan/common.c:522
kmalloc include/linux/slab.h:612 [inline]
sk_prot_alloc+0xe7/0x210 net/core/sock.c:1866
sk_alloc+0x2f/0x310 net/core/sock.c:1922
l2cap_sock_alloc+0x33/0x200 net/bluetooth/l2cap_sock.c:1867
l2cap_sock_new_connection_cb+0xd1/0x1c0 net/bluetooth/l2cap_sock.c:1479
l2cap_connect_cfm+0x35d/0x10d0 net/bluetooth/l2cap_core.c:8303
hci_connect_cfm include/net/bluetooth/hci_core.h:1505 [inline]
le_conn_complete_evt+0xdaf/0x1590 net/bluetooth/hci_event.c:5439
hci_le_conn_complete_evt net/bluetooth/hci_event.c:5464 [inline]
hci_le_meta_evt+0x289/0x3b80 net/bluetooth/hci_event.c:6186
hci_event_packet+0xe05/0x12f0 net/bluetooth/hci_event.c:6535
hci_rx_work+0x255/0xa10 net/bluetooth/hci_core.c:5160
process_one_work+0x863/0x1000 kernel/workqueue.c:2310
worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
kthread+0x436/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

Freed by task 15901:
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:46
kasan_set_free_info+0x1f/0x40 mm/kasan/generic.c:360
____kasan_slab_free+0xd5/0x110 mm/kasan/common.c:366
kasan_slab_free include/linux/kasan.h:230 [inline]
slab_free_hook mm/slub.c:1710 [inline]
slab_free_freelist_hook+0xea/0x170 mm/slub.c:1736
slab_free mm/slub.c:3504 [inline]
kfree+0xef/0x2a0 mm/slub.c:4564
sk_prot_free net/core/sock.c:1905 [inline]
__sk_destruct+0x578/0x840 net/core/sock.c:1991
l2cap_sock_cleanup_listen+0xda/0x270 net/bluetooth/l2cap_sock.c:1459
l2cap_sock_release+0x66/0x1e0 net/bluetooth/l2cap_sock.c:1420
__sock_release net/socket.c:651 [inline]
sock_close+0xd5/0x240 net/socket.c:1346
__fput+0x234/0x930 fs/file_table.c:311
task_work_run+0x125/0x1a0 kernel/task_work.c:188
exit_task_work include/linux/task_work.h:33 [inline]
do_exit+0x61e/0x20a0 kernel/exit.c:883
do_group_exit+0x12e/0x300 kernel/exit.c:997
get_signal+0x6ca/0x12c0 kernel/signal.c:2900
arch_do_signal_or_restart+0xc1/0x1300 arch/x86/kernel/signal.c:867
handle_signal_work kernel/entry/common.c:154 [inline]
exit_to_user_mode_loop+0x9e/0x130 kernel/entry/common.c:178
exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:214
__syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:307
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x66/0xd0

The buggy address belongs to the object at ffff88807bdc0000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 1360 bytes inside of
2048-byte region [ffff88807bdc0000, ffff88807bdc0800)
The buggy address belongs to the page:
page:ffffea0001ef7000 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7bdc0
head:ffffea0001ef7000 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 dead000000000100 dead000000000122 ffff888016842000
raw: 0000000000000000 0000000000080008 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 0x1d28c0(GFP_NOWAIT|__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 4288, ts 60655818127, free_ts 60606915048
prep_new_page mm/page_alloc.c:2426 [inline]
get_page_from_freelist+0x1b77/0x1c60 mm/page_alloc.c:4192
__alloc_pages+0x1e1/0x470 mm/page_alloc.c:5487
alloc_slab_page mm/slub.c:1780 [inline]
allocate_slab mm/slub.c:1917 [inline]
new_slab+0xc0/0x4b0 mm/slub.c:1980
___slab_alloc+0x81e/0xdf0 mm/slub.c:3013
__slab_alloc mm/slub.c:3100 [inline]
slab_alloc_node mm/slub.c:3191 [inline]
__kmalloc_node_track_caller+0x1fc/0x3a0 mm/slub.c:4963
kmalloc_reserve net/core/skbuff.c:356 [inline]
pskb_expand_head+0x127/0x10f0 net/core/skbuff.c:1709
netlink_trim+0x180/0x220 net/netlink/af_netlink.c:1299
netlink_broadcast_filtered+0x7c/0x1170 net/netlink/af_netlink.c:1511
netlink_broadcast net/netlink/af_netlink.c:1556 [inline]
nlmsg_multicast include/net/netlink.h:1033 [inline]
nlmsg_notify+0xec/0x1a0 net/netlink/af_netlink.c:2550
rtnl_notify net/core/rtnetlink.c:761 [inline]
rtmsg_ifinfo_send net/core/rtnetlink.c:3910 [inline]
rtmsg_ifinfo_event net/core/rtnetlink.c:3925 [inline]
rtnetlink_event+0x13a/0x1a0 net/core/rtnetlink.c:5735
notifier_call_chain kernel/notifier.c:83 [inline]
raw_notifier_call_chain+0xcb/0x160 kernel/notifier.c:391
call_netdevice_notifiers_extack net/core/dev.c:2061 [inline]
call_netdevice_notifiers net/core/dev.c:2075 [inline]
dev_set_mac_address+0x2c4/0x3d0 net/core/dev.c:9114
dev_set_mac_address_user+0x2d/0x50 net/core/dev.c:9128
do_setlink+0x80d/0x3980 net/core/rtnetlink.c:2736
__rtnl_newlink net/core/rtnetlink.c:3452 [inline]
rtnl_newlink+0x1419/0x17d0 net/core/rtnetlink.c:3574
rtnetlink_rcv_msg+0x7ff/0xe90 net/core/rtnetlink.c:5684
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1340 [inline]
free_pcp_prepare mm/page_alloc.c:1391 [inline]
free_unref_page_prepare+0x637/0x6c0 mm/page_alloc.c:3317
free_unref_page+0x94/0x280 mm/page_alloc.c:3396
qlist_free_all+0x35/0x90 mm/kasan/quarantine.c:176
kasan_quarantine_reduce+0x150/0x160 mm/kasan/quarantine.c:283
__kasan_slab_alloc+0x2f/0xd0 mm/kasan/common.c:444
kasan_slab_alloc include/linux/kasan.h:254 [inline]
slab_post_alloc_hook+0x4c/0x380 mm/slab.h:519
slab_alloc_node mm/slub.c:3225 [inline]
kmem_cache_alloc_node+0x12d/0x2d0 mm/slub.c:3261
__alloc_skb+0xf4/0x750 net/core/skbuff.c:415
alloc_skb include/linux/skbuff.h:1162 [inline]
nlmsg_new include/net/netlink.h:953 [inline]
inet_netconf_notify_devconf+0x16f/0x230 net/ipv4/devinet.c:2121
__devinet_sysctl_unregister net/ipv4/devinet.c:2630 [inline]
devinet_sysctl_unregister net/ipv4/devinet.c:2654 [inline]
inetdev_destroy net/ipv4/devinet.c:326 [inline]
inetdev_event+0x71c/0x1360 net/ipv4/devinet.c:1611
notifier_call_chain kernel/notifier.c:83 [inline]
raw_notifier_call_chain+0xcb/0x160 kernel/notifier.c:391
call_netdevice_notifiers_extack net/core/dev.c:2061 [inline]
call_netdevice_notifiers net/core/dev.c:2075 [inline]
unregister_netdevice_many+0xf57/0x18f0 net/core/dev.c:11134
sit_exit_batch_net+0x498/0x4e0 net/ipv6/sit.c:1952
ops_exit_list net/core/net_namespace.c:177 [inline]
cleanup_net+0x77b/0xb80 net/core/net_namespace.c:635
process_one_work+0x863/0x1000 kernel/workqueue.c:2310
worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457

Memory state around the buggy address:
ffff88807bdc0400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88807bdc0480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88807bdc0500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88807bdc0580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88807bdc0600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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