From: Cen Zhang Date: Tue, 23 Jun 2026 16:12:59 +0000 (+0800) Subject: Bluetooth: 6lowpan: hold L2CAP conn across debugfs control X-Git-Tag: v7.2-rc3~29^2~13^2~10 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=518aa9505fa10ea5662349e5d2efd8c9e32a820b;p=thirdparty%2Fkernel%2Flinux.git Bluetooth: 6lowpan: hold L2CAP conn across debugfs control get_l2cap_conn() looks up an LE hci_conn under hdev protection, but then drops that protection before reading hcon->l2cap_data and before lowpan_control_write() later dereferences conn->hcon. A disconnect or device close can tear down the same L2CAP connection in that window. The buggy scenario involves two paths, with each column showing the order within that path: 6LoWPAN control write: HCI disconnect/device close: 1. get_l2cap_conn() finds hcon 1. hci_disconn_cfm() dispatches and hcon->l2cap_data. the L2CAP disconnect callback. 2. get_l2cap_conn() drops hdev 2. l2cap_conn_del() clears protection and returns conn. hcon->l2cap_data and drops the L2CAP connection reference. 3. lowpan_control_write() reads 3. hci_conn_del() removes and drops conn->hcon. the HCI connection. Take a reference to the L2CAP connection with l2cap_conn_hold_unless_zero() while hdev is still locked, and drop that reference after the debugfs command's last use of conn. This mirrors the existing L2CAP ACL receive-side handoff and keeps the connection dereferenceable after leaving hdev protection. Export the existing helper so the bluetooth_6lowpan module can use the same lifetime primitive. Validation reproduced this kernel report: BUG: KASAN: slab-use-after-free in lowpan_control_write+0x374/0x520 The buggy address belongs to the object at ffff888111b9d000 which belongs to the cache kmalloc-1k of size 1024 The buggy address is located 0 bytes inside of freed 1024-byte region [ffff888111b9d000, ffff888111b9d400) Read of size 8 Call trace: dump_stack_lvl+0x66/0xa0 print_report+0xce/0x5f0 lowpan_control_write+0x374/0x520 (net/bluetooth/6lowpan.c:1131) srso_alias_return_thunk+0x5/0xfbef5 __virt_addr_valid+0x19f/0x330 kasan_report+0xe0/0x110 __debugfs_file_get+0xf7/0x400 full_proxy_write+0x9e/0xd0 vfs_write+0x1b0/0x810 ksys_write+0xd2/0x170 dnotify_flush+0x32/0x220 do_syscall_64+0x115/0x6a0 (arch/x86/entry/syscall_64.c:87) entry_SYSCALL_64_after_hwframe+0x77/0x7f Allocated by task stack: kasan_save_stack+0x33/0x60 kasan_save_track+0x17/0x60 __kasan_kmalloc+0xaa/0xb0 l2cap_conn_add+0x45/0x520 l2cap_chan_connect+0xac6/0xd90 l2cap_sock_connect+0x216/0x350 __sys_connect+0x101/0x130 __x64_sys_connect+0x40/0x50 do_syscall_64+0x115/0x6a0 (arch/x86/entry/syscall_64.c:87) entry_SYSCALL_64_after_hwframe+0x77/0x7f Freed by task stack: kasan_save_stack+0x33/0x60 kasan_save_track+0x17/0x60 kasan_save_free_info+0x3b/0x60 __kasan_slab_free+0x5f/0x80 kfree+0x313/0x590 hci_conn_hash_flush+0xc0/0x140 hci_dev_close_sync+0x41a/0xb00 hci_dev_close+0x12f/0x160 hci_sock_ioctl+0x157/0x570 sock_do_ioctl+0xf7/0x210 sock_ioctl+0x32f/0x490 __x64_sys_ioctl+0xc7/0x110 do_syscall_64+0x115/0x6a0 (arch/x86/entry/syscall_64.c:87) entry_SYSCALL_64_after_hwframe+0x77/0x7f kasan_record_aux_stack+0xa7/0xc0 insert_work+0x32/0x100 __queue_work+0x262/0xa60 queue_work_on+0xad/0xb0 l2cap_connect_cfm+0x4ef/0x670 hci_le_remote_feat_complete_evt+0x247/0x430 hci_event_packet+0x360/0x6f0 hci_rx_work+0x2ae/0x7a0 process_one_work+0x4fd/0xbc0 worker_thread+0x2d8/0x570 kthread+0x1ad/0x1f0 ret_from_fork+0x3c9/0x540 ret_from_fork_asm+0x1a/0x30 Fixes: 6b8d4a6a0314 ("Bluetooth: 6LoWPAN: Use connected oriented channel instead of fixed one") Assisted-by: Codex:gpt-5.5 Signed-off-by: Cen Zhang Signed-off-by: Luiz Augusto von Dentz --- diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c index c4b0a4048be2..e7be18a3af33 100644 --- a/net/bluetooth/6lowpan.c +++ b/net/bluetooth/6lowpan.c @@ -1017,16 +1017,19 @@ static int get_l2cap_conn(char *buf, bdaddr_t *addr, u8 *addr_type, hci_dev_lock(hdev); hcon = hci_conn_hash_lookup_le(hdev, addr, le_addr_type); - hci_dev_unlock(hdev); - hci_dev_put(hdev); - - if (!hcon) + if (!hcon) { + hci_dev_unlock(hdev); + hci_dev_put(hdev); return -ENOENT; + } - *conn = (struct l2cap_conn *)hcon->l2cap_data; + *conn = l2cap_conn_hold_unless_zero(hcon->l2cap_data); BT_DBG("conn %p dst %pMR type %u", *conn, &hcon->dst, hcon->dst_type); + hci_dev_unlock(hdev); + hci_dev_put(hdev); + return 0; } @@ -1154,18 +1157,22 @@ static ssize_t lowpan_control_write(struct file *fp, if (conn) { struct lowpan_peer *peer; - if (!is_bt_6lowpan(conn->hcon)) + if (!is_bt_6lowpan(conn->hcon)) { + l2cap_conn_put(conn); return -EINVAL; + } peer = lookup_peer(conn); if (peer) { BT_DBG("6LoWPAN connection already exists"); + l2cap_conn_put(conn); return -EALREADY; } BT_DBG("conn %p dst %pMR type %d user %u", conn, &conn->hcon->dst, conn->hcon->dst_type, addr_type); + l2cap_conn_put(conn); } ret = bt_6lowpan_connect(&addr, addr_type); @@ -1181,6 +1188,8 @@ static ssize_t lowpan_control_write(struct file *fp, return ret; ret = bt_6lowpan_disconnect(conn, addr_type); + if (conn) + l2cap_conn_put(conn); if (ret < 0) return ret; diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index a1d249f42be7..4ee3b9e30c65 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -7716,6 +7716,7 @@ struct l2cap_conn *l2cap_conn_hold_unless_zero(struct l2cap_conn *c) return c; } +EXPORT_SYMBOL(l2cap_conn_hold_unless_zero); int l2cap_recv_acldata(struct hci_dev *hdev, u16 handle, struct sk_buff *skb, u16 flags)