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Message-ID: <f1b9fe3939dff426528760eca39d4ad4ab2340a3.camel@iki.fi>
Subject: Re: [PATCH] Bluetooth: Fix UAF for hci_chan
From:   Pauli Virtanen <pav@iki.fi>
To:     Ziyang Xuan <william.xuanziyang@huawei.com>
Cc:     linux-kernel@vger.kernel.org
Date:   Sat, 07 Oct 2023 13:44:30 +0300
In-Reply-To: <20231007093521.2404844-1-william.xuanziyang@huawei.com>
References: <20231007093521.2404844-1-william.xuanziyang@huawei.com>
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Hi,

la, 2023-10-07 kello 17:35 +0800, Ziyang Xuan kirjoitti:
> Syzbot reports a UAF problem as follows:
>=20
> BUG: KASAN: slab-use-after-free in hci_send_acl+0x48/0xe70 net/bluetooth/=
hci_core.c:3231
> ...
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
>  print_address_description mm/kasan/report.c:364 [inline]
>  print_report+0x163/0x540 mm/kasan/report.c:475
>  kasan_report+0x175/0x1b0 mm/kasan/report.c:588
>  hci_send_acl+0x48/0xe70 net/bluetooth/hci_core.c:3231
>  l2cap_send_conn_req net/bluetooth/l2cap_core.c:1286 [inline]
>  l2cap_start_connection+0x465/0x620 net/bluetooth/l2cap_core.c:1514
>  l2cap_conn_start+0xbf3/0x1130 net/bluetooth/l2cap_core.c:1661
>  process_one_work kernel/workqueue.c:2630 [inline]
>  process_scheduled_works+0x90f/0x1400 kernel/workqueue.c:2703
>  worker_thread+0xa5f/0xff0 kernel/workqueue.c:2784
>  kthread+0x2d3/0x370 kernel/kthread.c:388
>  ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:147
>  ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:304
>  </TASK>

Note this looks like the same issue as in the following thread, where
there's a suggestion from maintainer:

https://lore.kernel.org/linux-bluetooth/fd9c0f0eddb8a7d73e9797568dc3cf2bc9b=
8ad62.1696077070.git.pav@iki.fi/T/#u


Is it the same issue?

>=20
> Allocated by task 27110:
>  kasan_save_stack mm/kasan/common.c:45 [inline]
>  kasan_set_track+0x4f/0x70 mm/kasan/common.c:52
>  ____kasan_kmalloc mm/kasan/common.c:374 [inline]
>  __kasan_kmalloc+0x98/0xb0 mm/kasan/common.c:383
>  kmalloc include/linux/slab.h:599 [inline]
>  kzalloc include/linux/slab.h:720 [inline]
>  hci_chan_create+0xc8/0x300 net/bluetooth/hci_conn.c:2714
>  l2cap_conn_add+0x69/0xc10 net/bluetooth/l2cap_core.c:7841
>  l2cap_chan_connect+0x61f/0xeb0 net/bluetooth/l2cap_core.c:8053
>  bt_6lowpan_connect net/bluetooth/6lowpan.c:894 [inline]
>  lowpan_control_write+0x55e/0x850 net/bluetooth/6lowpan.c:1129
>  full_proxy_write+0x113/0x1c0 fs/debugfs/file.c:236
>  vfs_write+0x286/0xaf0 fs/read_write.c:582
>  ksys_write+0x1a0/0x2c0 fs/read_write.c:637
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
>=20
> Freed by task 5067:
>  kasan_save_stack mm/kasan/common.c:45 [inline]
>  kasan_set_track+0x4f/0x70 mm/kasan/common.c:52
>  kasan_save_free_info+0x28/0x40 mm/kasan/generic.c:522
>  ____kasan_slab_free+0xd6/0x120 mm/kasan/common.c:236
>  kasan_slab_free include/linux/kasan.h:164 [inline]
>  slab_free_hook mm/slub.c:1800 [inline]
>  slab_free_freelist_hook mm/slub.c:1826 [inline]
>  slab_free mm/slub.c:3809 [inline]
>  __kmem_cache_free+0x25f/0x3b0 mm/slub.c:3822
>  hci_chan_list_flush net/bluetooth/hci_conn.c:2754 [inline]
>  hci_conn_cleanup net/bluetooth/hci_conn.c:152 [inline]
>  hci_conn_del+0x4f8/0xc40 net/bluetooth/hci_conn.c:1156
>  hci_abort_conn_sync+0xa45/0xfe0
>  hci_cmd_sync_work+0x228/0x400 net/bluetooth/hci_sync.c:306
>  process_one_work kernel/workqueue.c:2630 [inline]
>  process_scheduled_works+0x90f/0x1400 kernel/workqueue.c:2703
>  worker_thread+0xa5f/0xff0 kernel/workqueue.c:2784
>  kthread+0x2d3/0x370 kernel/kthread.c:388
>  ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:147
>  ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:304
>=20
> There are two main reasons for this:
> 1. In the case of hci_conn_add() concurrency, the handle of
> hci_conn allocated through hci_conn_hash_alloc_unset() is not unique.
> 2. The processes related to hci_abort_conn() and hci_connect_xxx()
> can be concurrent, but the two processes lack synchronization.
>=20
> To fix this, use ida to manage the allocation of conn->handle, and
> add the HCI_CONN_DISC flag to achieve synchronization between
> hci_abort_conn() and hci_connect_xxx() related processes.
>=20
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
> ---
>  include/net/bluetooth/hci_core.h | 17 ++++++++++----
>  net/bluetooth/hci_conn.c         | 39 ++++++++++++++++----------------
>  net/bluetooth/hci_core.c         |  3 +++
>  3 files changed, 35 insertions(+), 24 deletions(-)
>=20
> diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci=
_core.h
> index e6359f7346f1..72818fc49ccd 100644
> --- a/include/net/bluetooth/hci_core.h
> +++ b/include/net/bluetooth/hci_core.h
> @@ -350,6 +350,8 @@ struct hci_dev {
>  	struct list_head list;
>  	struct mutex	lock;
> =20
> +	struct ida	unset_handle_ida;
> +
>  	char		name[8];
>  	unsigned long	flags;
>  	__u16		id;
> @@ -969,6 +971,7 @@ enum {
>  	HCI_CONN_AUTH_INITIATOR,
>  	HCI_CONN_DROP,
>  	HCI_CONN_CANCEL,
> +	HCI_CONN_DISC,
>  	HCI_CONN_PARAM_REMOVAL_PEND,
>  	HCI_CONN_NEW_LINK_KEY,
>  	HCI_CONN_SCANNING,
> @@ -1174,7 +1177,8 @@ static inline struct hci_conn *hci_conn_hash_lookup=
_ba(struct hci_dev *hdev,
>  	rcu_read_lock();
> =20
>  	list_for_each_entry_rcu(c, &h->list, list) {
> -		if (c->type =3D=3D type && !bacmp(&c->dst, ba)) {
> +		if (c->type =3D=3D type && !bacmp(&c->dst, ba) &&
> +		    !test_bit(HCI_CONN_DISC, &c->flags)) {
>  			rcu_read_unlock();
>  			return c;
>  		}
> @@ -1195,8 +1199,9 @@ static inline struct hci_conn *hci_conn_hash_lookup=
_le(struct hci_dev *hdev,
>  	rcu_read_lock();
> =20
>  	list_for_each_entry_rcu(c, &h->list, list) {
> -		if (c->type !=3D LE_LINK)
> -		       continue;
> +		if (c->type !=3D LE_LINK ||
> +		    test_bit(HCI_CONN_DISC, &c->flags))
> +			continue;
> =20
>  		if (ba_type =3D=3D c->dst_type && !bacmp(&c->dst, ba)) {
>  			rcu_read_unlock();
> @@ -1386,7 +1391,8 @@ static inline struct hci_conn *hci_lookup_le_connec=
t(struct hci_dev *hdev)
> =20
>  	list_for_each_entry_rcu(c, &h->list, list) {
>  		if (c->type =3D=3D LE_LINK && c->state =3D=3D BT_CONNECT &&
> -		    !test_bit(HCI_CONN_SCANNING, &c->flags)) {
> +		    !test_bit(HCI_CONN_SCANNING, &c->flags) &&
> +		    !test_bit(HCI_CONN_DISC, &c->flags)) {
>  			rcu_read_unlock();
>  			return c;
>  		}
> @@ -1520,7 +1526,8 @@ static inline void hci_conn_drop(struct hci_conn *c=
onn)
>  {
>  	BT_DBG("hcon %p orig refcnt %d", conn, atomic_read(&conn->refcnt));
> =20
> -	if (atomic_dec_and_test(&conn->refcnt)) {
> +	if (atomic_dec_and_test(&conn->refcnt) &&
> +	    !test_bit(HCI_CONN_DISC, &conn->flags)) {
>  		unsigned long timeo;
> =20
>  		switch (conn->type) {
> diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
> index 9d5057cef30a..6045d32e28d3 100644
> --- a/net/bluetooth/hci_conn.c
> +++ b/net/bluetooth/hci_conn.c
> @@ -153,6 +153,9 @@ static void hci_conn_cleanup(struct hci_conn *conn)
> =20
>  	hci_conn_hash_del(hdev, conn);
> =20
> +	if (HCI_CONN_HANDLE_UNSET(conn->handle))
> +		ida_free(&hdev->unset_handle_ida, conn->handle);
> +
>  	if (conn->cleanup)
>  		conn->cleanup(conn);
> =20
> @@ -928,29 +931,17 @@ static void cis_cleanup(struct hci_conn *conn)
>  	hci_le_remove_cig(hdev, conn->iso_qos.ucast.cig);
>  }
> =20
> -static u16 hci_conn_hash_alloc_unset(struct hci_dev *hdev)
> +static int hci_conn_hash_alloc_unset(struct hci_dev *hdev)
>  {
> -	struct hci_conn_hash *h =3D &hdev->conn_hash;
> -	struct hci_conn  *c;
> -	u16 handle =3D HCI_CONN_HANDLE_MAX + 1;
> -
> -	rcu_read_lock();
> -
> -	list_for_each_entry_rcu(c, &h->list, list) {
> -		/* Find the first unused handle */
> -		if (handle =3D=3D 0xffff || c->handle !=3D handle)
> -			break;
> -		handle++;
> -	}
> -	rcu_read_unlock();
> -
> -	return handle;
> +	return ida_alloc_range(&hdev->unset_handle_ida, HCI_CONN_HANDLE_MAX + 1=
,
> +			       U16_MAX, GFP_ATOMIC);
>  }
> =20
>  struct hci_conn *hci_conn_add(struct hci_dev *hdev, int type, bdaddr_t *=
dst,
>  			      u8 role)
>  {
>  	struct hci_conn *conn;
> +	int handle;
> =20
>  	BT_DBG("%s dst %pMR", hdev->name, dst);
> =20
> @@ -960,7 +951,12 @@ struct hci_conn *hci_conn_add(struct hci_dev *hdev, =
int type, bdaddr_t *dst,
> =20
>  	bacpy(&conn->dst, dst);
>  	bacpy(&conn->src, &hdev->bdaddr);
> -	conn->handle =3D hci_conn_hash_alloc_unset(hdev);
> +	handle =3D hci_conn_hash_alloc_unset(hdev);
> +	if (unlikely(handle < 0)) {
> +		kfree(conn);
> +		return NULL;
> +	}
> +	conn->handle =3D handle;
>  	conn->hdev  =3D hdev;
>  	conn->type  =3D type;
>  	conn->role  =3D role;
> @@ -2897,6 +2893,7 @@ static int abort_conn_sync(struct hci_dev *hdev, vo=
id *data)
>  int hci_abort_conn(struct hci_conn *conn, u8 reason)
>  {
>  	struct hci_dev *hdev =3D conn->hdev;
> +	int ret;
> =20
>  	/* If abort_reason has already been set it means the connection is
>  	 * already being aborted so don't attempt to overwrite it.
> @@ -2925,6 +2922,10 @@ int hci_abort_conn(struct hci_conn *conn, u8 reaso=
n)
>  		}
>  	}
> =20
> -	return hci_cmd_sync_queue(hdev, abort_conn_sync, UINT_PTR(conn->handle)=
,
> -				  NULL);
> +	ret =3D hci_cmd_sync_queue(hdev, abort_conn_sync,
> +				 UINT_PTR(conn->handle), NULL);
> +	if (!ret)
> +		set_bit(HCI_CONN_DISC, &conn->flags);
> +
> +	return ret;
>  }
> diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
> index a5992f1b3c9b..67b652c18a44 100644
> --- a/net/bluetooth/hci_core.c
> +++ b/net/bluetooth/hci_core.c
> @@ -2535,6 +2535,8 @@ struct hci_dev *hci_alloc_dev_priv(int sizeof_priv)
>  	mutex_init(&hdev->lock);
>  	mutex_init(&hdev->req_lock);
> =20
> +	ida_init(&hdev->unset_handle_ida);
> +
>  	INIT_LIST_HEAD(&hdev->mesh_pending);
>  	INIT_LIST_HEAD(&hdev->mgmt_pending);
>  	INIT_LIST_HEAD(&hdev->reject_list);
> @@ -2786,6 +2788,7 @@ void hci_release_dev(struct hci_dev *hdev)
>  	hci_blocked_keys_clear(hdev);
>  	hci_dev_unlock(hdev);
> =20
> +	ida_destroy(&hdev->unset_handle_ida);
>  	ida_simple_remove(&hci_index_ida, hdev->id);
>  	kfree_skb(hdev->sent_cmd);
>  	kfree_skb(hdev->recv_event);

--=20
Pauli Virtanen