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In-Reply-To: <31d160847c8f790a7e45f9bae4146d436813d0bb.camel@iki.fi>
From:   Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Date:   Fri, 9 Jun 2023 11:34:06 -0700
Message-ID: <CABBYNZLwN8qp78qPb1nb4u6Fh76XQBx0vHpqWQbRWggDBbedJA@mail.gmail.com>
Subject: Re: [PATCH 1/3] Bluetooth: hci_sync: iterate over hci_conn_params safely
To:     Pauli Virtanen <pav@iki.fi>
Cc:     linux-bluetooth@vger.kernel.org
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Precedence: bulk

Hi Pauli,

On Fri, Jun 9, 2023 at 11:22=E2=80=AFAM Pauli Virtanen <pav@iki.fi> wrote:
>
> Hi Luiz,
>
> pe, 2023-06-09 kello 10:19 -0700, Luiz Augusto von Dentz kirjoitti:
> > On Thu, Jun 8, 2023 at 2:10=E2=80=AFPM Pauli Virtanen <pav@iki.fi> wrot=
e:
> > >
> > > hci_update_accept_list_sync iterates over hdev->pend_le_conns and
> > > hdev->pend_le_reports, and waits for controller events in the loop bo=
dy,
> > > without holding hdev lock.
> > >
> > > Meanwhile, these lists and the items may be modified e.g. by
> > > le_scan_cleanup.  This can invalidate the list cursor in the ongoing
> > > iterations, resulting to invalid behavior (eg use-after-free).
> > >
> > > hdev lock should be held when operating on these lists, but it cannot=
 be
> > > held in the loop bodies here as they block. The loops are in hci_sync=
,
> > > so at most one loop runs at a time (per hdev).
> > >
> > > Fix this by doing the iteration in a safe way vs. list mutation, and
> > > copy data to avoid locking. Add hci_conn_params.add_pending flag to
> > > track which items are left.
> > >
> > > Lock also around hci_pend_le_action_lookup there.
> > >
> > > This fixes the following, which can be triggered at least by changing
> > > hci_le_set_cig_params to always return false, and running BlueZ
> > > iso-tester, which causes connections to be created and dropped fast:
> > >
> > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > > BUG: KASAN: slab-use-after-free in hci_update_passive_scan_sync (net/=
bluetooth/hci_sync.c:2536 net/bluetooth/hci_sync.c:2723 net/bluetooth/hci_s=
ync.c:2841)
> > > Read of size 8 at addr ffff888001265018 by task kworker/u3:0/32
> > >
> > > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-1.fc3=
8 04/01/2014
> > > Workqueue: hci0 hci_cmd_sync_work
> > > Call Trace:
> > > <TASK>
> > > dump_stack_lvl (./arch/x86/include/asm/irqflags.h:134 lib/dump_stack.=
c:107)
> > > print_report (mm/kasan/report.c:320 mm/kasan/report.c:430)
> > > ? __virt_addr_valid (./include/linux/mmzone.h:1915 ./include/linux/mm=
zone.h:2011 arch/x86/mm/physaddr.c:65)
> > > ? hci_update_passive_scan_sync (net/bluetooth/hci_sync.c:2536 net/blu=
etooth/hci_sync.c:2723 net/bluetooth/hci_sync.c:2841)
> > > kasan_report (mm/kasan/report.c:538)
> > > ? hci_update_passive_scan_sync (net/bluetooth/hci_sync.c:2536 net/blu=
etooth/hci_sync.c:2723 net/bluetooth/hci_sync.c:2841)
> > > hci_update_passive_scan_sync (net/bluetooth/hci_sync.c:2536 net/bluet=
ooth/hci_sync.c:2723 net/bluetooth/hci_sync.c:2841)
> > > ? __pfx_hci_update_passive_scan_sync (net/bluetooth/hci_sync.c:2780)
> > > ? mutex_lock (kernel/locking/mutex.c:282)
> > > ? __pfx_mutex_lock (kernel/locking/mutex.c:282)
> > > ? __pfx_mutex_unlock (kernel/locking/mutex.c:538)
> > > ? __pfx_update_passive_scan_sync (net/bluetooth/hci_sync.c:2861)
> > > hci_cmd_sync_work (net/bluetooth/hci_sync.c:306)
> > > process_one_work (./arch/x86/include/asm/preempt.h:27 kernel/workqueu=
e.c:2399)
> > > worker_thread (./include/linux/list.h:292 kernel/workqueue.c:2538)
> > > ? __pfx_worker_thread (kernel/workqueue.c:2480)
> > > kthread (kernel/kthread.c:376)
> > > ? __pfx_kthread (kernel/kthread.c:331)
> > > ret_from_fork (arch/x86/entry/entry_64.S:314)
> > > </TASK>
> > >
> > > Allocated by task 31:
> > > kasan_save_stack (mm/kasan/common.c:46)
> > > kasan_set_track (mm/kasan/common.c:52)
> > > __kasan_kmalloc (mm/kasan/common.c:374 mm/kasan/common.c:383)
> > > hci_conn_params_add (./include/linux/slab.h:580 ./include/linux/slab.=
h:720 net/bluetooth/hci_core.c:2277)
> > > hci_connect_le_scan (net/bluetooth/hci_conn.c:1419 net/bluetooth/hci_=
conn.c:1589)
> > > hci_connect_cis (net/bluetooth/hci_conn.c:2266)
> > > iso_connect_cis (net/bluetooth/iso.c:390)
> > > iso_sock_connect (net/bluetooth/iso.c:899)
> > > __sys_connect (net/socket.c:2003 net/socket.c:2020)
> > > __x64_sys_connect (net/socket.c:2027)
> > > do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
> > > entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120)
> > >
> > > Freed by task 15:
> > > kasan_save_stack (mm/kasan/common.c:46)
> > > kasan_set_track (mm/kasan/common.c:52)
> > > kasan_save_free_info (mm/kasan/generic.c:523)
> > > __kasan_slab_free (mm/kasan/common.c:238 mm/kasan/common.c:200 mm/kas=
an/common.c:244)
> > > __kmem_cache_free (mm/slub.c:1807 mm/slub.c:3787 mm/slub.c:3800)
> > > hci_conn_params_del (net/bluetooth/hci_core.c:2323)
> > > le_scan_cleanup (net/bluetooth/hci_conn.c:202)
> > > process_one_work (./arch/x86/include/asm/preempt.h:27 kernel/workqueu=
e.c:2399)
> > > worker_thread (./include/linux/list.h:292 kernel/workqueue.c:2538)
> > > kthread (kernel/kthread.c:376)
> > > ret_from_fork (arch/x86/entry/entry_64.S:314)
> > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > >
> > > Fixes: e8907f76544f ("Bluetooth: hci_sync: Make use of hci_cmd_sync_q=
ueue set 3")
> > > Signed-off-by: Pauli Virtanen <pav@iki.fi>
> > > ---
> > >
> > > Notes:
> > >     It might be that even more of hci_passive_scan_sync and the routi=
nes it
> > >     calls should hold hdev->lock, but don't know that right now.
> > >
> > >  include/net/bluetooth/hci_core.h |  1 +
> > >  net/bluetooth/hci_sync.c         | 81 ++++++++++++++++++++++++++++--=
--
> > >  2 files changed, 74 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth=
/hci_core.h
> > > index 683666ea210c..e79b3831fcf3 100644
> > > --- a/include/net/bluetooth/hci_core.h
> > > +++ b/include/net/bluetooth/hci_core.h
> > > @@ -822,6 +822,7 @@ struct hci_conn_params {
> > >
> > >         struct hci_conn *conn;
> > >         bool explicit_connect;
> > > +       bool add_pending;
> > >         hci_conn_flags_t flags;
> > >         u8  privacy_mode;
> > >  };
> > > diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
> > > index 97da5bcaa904..e6fde15dc9ca 100644
> > > --- a/net/bluetooth/hci_sync.c
> > > +++ b/net/bluetooth/hci_sync.c
> > > @@ -2160,15 +2160,23 @@ static int hci_le_del_accept_list_sync(struct=
 hci_dev *hdev,
> > >         return 0;
> > >  }
> > >
> > > +struct conn_params {
> > > +       bdaddr_t addr;
> > > +       u8 addr_type;
> > > +       hci_conn_flags_t flags;
> > > +       u8 privacy_mode;
> > > +};
> > > +
> > >  /* Adds connection to resolve list if needed.
> > >   * Setting params to NULL programs local hdev->irk
> > >   */
> > >  static int hci_le_add_resolve_list_sync(struct hci_dev *hdev,
> > > -                                       struct hci_conn_params *param=
s)
> > > +                                       struct conn_params *params)
> > >  {
> > >         struct hci_cp_le_add_to_resolv_list cp;
> > >         struct smp_irk *irk;
> > >         struct bdaddr_list_with_irk *entry;
> > > +       struct hci_conn_params *hparams;
> > >
> > >         if (!use_ll_privacy(hdev))
> > >                 return 0;
> > > @@ -2203,6 +2211,13 @@ static int hci_le_add_resolve_list_sync(struct=
 hci_dev *hdev,
> > >         /* Default privacy mode is always Network */
> > >         params->privacy_mode =3D HCI_NETWORK_PRIVACY;
> > >
> > > +       hci_dev_lock(hdev);
> > > +       hparams =3D hci_conn_params_lookup(hdev, &params->addr,
> > > +                                        params->addr_type);
> > > +       if (hparams)
> > > +               hparams->privacy_mode =3D HCI_NETWORK_PRIVACY;
> > > +       hci_dev_unlock(hdev);
> > > +
> > >  done:
> > >         if (hci_dev_test_flag(hdev, HCI_PRIVACY))
> > >                 memcpy(cp.local_irk, hdev->irk, 16);
> > > @@ -2215,7 +2230,7 @@ static int hci_le_add_resolve_list_sync(struct =
hci_dev *hdev,
> > >
> > >  /* Set Device Privacy Mode. */
> > >  static int hci_le_set_privacy_mode_sync(struct hci_dev *hdev,
> > > -                                       struct hci_conn_params *param=
s)
> > > +                                       struct conn_params *params)
> > >  {
> > >         struct hci_cp_le_set_privacy_mode cp;
> > >         struct smp_irk *irk;
> > > @@ -2249,7 +2264,7 @@ static int hci_le_set_privacy_mode_sync(struct =
hci_dev *hdev,
> > >   * properly set the privacy mode.
> > >   */
> > >  static int hci_le_add_accept_list_sync(struct hci_dev *hdev,
> > > -                                      struct hci_conn_params *params=
,
> > > +                                      struct conn_params *params,
> > >                                        u8 *num_entries)
> > >  {
> > >         struct hci_cp_le_add_to_accept_list cp;
> > > @@ -2447,6 +2462,37 @@ struct sk_buff *hci_read_local_oob_data_sync(s=
truct hci_dev *hdev,
> > >         return __hci_cmd_sync_sk(hdev, opcode, 0, NULL, 0, HCI_CMD_TI=
MEOUT, sk);
> > >  }
> > >
> > > +static void conn_params_iter_init(struct list_head *list)
> > > +{
> > > +       struct hci_conn_params *params;
> > > +
> > > +       list_for_each_entry(params, list, action)
> > > +               params->add_pending =3D true;
> > > +}
> > > +
> > > +static bool conn_params_iter_next(struct list_head *list,
> > > +                                 struct conn_params *item)
> > > +{
> > > +       struct hci_conn_params *params;
> > > +
> > > +       /* Must hold hdev lock. Not reentrant. Mutating list is allow=
ed. */
> > > +
> > > +       list_for_each_entry(params, list, action) {
> > > +               if (!params->add_pending)
> > > +                       continue;
> > > +
> > > +               memcpy(&item->addr, &params->addr, sizeof(params->add=
r));
> > > +               item->addr_type =3D params->addr_type;
> > > +               item->privacy_mode =3D params->privacy_mode;
> > > +               item->flags =3D params->flags;
> > > +
> > > +               params->add_pending =3D false;
> > > +               return true;
> > > +       }
> > > +
> > > +       return false;
> > > +}
> >
> > I wonder if we shouldn't take the approach of hci_lookup_connect_le
> > though, it uses rcu_read_lock + list_for_each_entry_rcu which seems to
> > be more efficient than having a dedicated lock to protect the list.
>
> It could use RCU in this function instead of hdev->lock, we'd need to
> change the several places where the list is modified though. I can
> change that if it's better that way (I don't have a good idea which is
> more efficient, or if this list is "mostly-read" one).

We have been extensively using it for hci_conn lists though so I'd
give it a try.

>
> I'm not sure RCU would help getting rid of the add_pending flag or
> copying the params data though: IIUC, RCU does not guarantee items or
> the list cursor stay alive once you leave the read side critical
> section (Documentation/RCU/checklist.rst point 2). If it's like this,
> it wouldn't be allowed to rcu_read_unlock in the loop body, and then
> rcu_read_lock again and continue the iteration, and we'd need a lock or
> data copy to prevent params from being freed.

Yeah, I got that doing RCU unlock+lock pattern on a loop is not going
to be safe, but it is not that different than using a dedicated lock
either since once you unlock other threats can modify the data as
well, so RCU only really help us not introducing more and more locks
to protect lists for example.

>
> > >  /* Device must not be scanning when updating the accept list.
> > >   *
> > >   * Update is done using the following sequence:
> > > @@ -2466,7 +2512,7 @@ struct sk_buff *hci_read_local_oob_data_sync(st=
ruct hci_dev *hdev,
> > >   */
> > >  static u8 hci_update_accept_list_sync(struct hci_dev *hdev)
> > >  {
> > > -       struct hci_conn_params *params;
> > > +       struct conn_params params;
> > >         struct bdaddr_list *b, *t;
> > >         u8 num_entries =3D 0;
> > >         bool pend_conn, pend_report;
> > > @@ -2494,6 +2540,8 @@ static u8 hci_update_accept_list_sync(struct hc=
i_dev *hdev)
> > >                 goto done;
> > >         }
> > >
> > > +       hci_dev_lock(hdev);
> > > +
> > >         /* Go through the current accept list programmed into the
> > >          * controller one by one and check if that address is connect=
ed or is
> > >          * still in the list of pending connections or list of device=
s to
> > > @@ -2515,8 +2563,10 @@ static u8 hci_update_accept_list_sync(struct h=
ci_dev *hdev)
> > >                  * remove it from the acceptlist.
> > >                  */
> > >                 if (!pend_conn && !pend_report) {
> > > +                       hci_dev_unlock(hdev);
> > >                         hci_le_del_accept_list_sync(hdev, &b->bdaddr,
> > >                                                     b->bdaddr_type);
> > > +                       hci_dev_lock(hdev);
> > >                         continue;
> > >                 }
> > >
> > > @@ -2532,23 +2582,38 @@ static u8 hci_update_accept_list_sync(struct =
hci_dev *hdev)
> > >          * available accept list entries in the controller, then
> > >          * just abort and return filer policy value to not use the
> > >          * accept list.
> > > +        *
> > > +        * The list may be mutated at any time outside hdev lock,
> > > +        * so use special iteration with copies.
> > >          */
> > > -       list_for_each_entry(params, &hdev->pend_le_conns, action) {
> > > -               err =3D hci_le_add_accept_list_sync(hdev, params, &nu=
m_entries);
> > > +
> > > +       conn_params_iter_init(&hdev->pend_le_conns);
> > > +
> > > +       while (conn_params_iter_next(&hdev->pend_le_conns, &params)) =
{
> > > +               hci_dev_unlock(hdev);
> > > +               err =3D hci_le_add_accept_list_sync(hdev, &params, &n=
um_entries);
> > >                 if (err)
> > >                         goto done;
> > > +               hci_dev_lock(hdev);
> > >         }
> > >
> > >         /* After adding all new pending connections, walk through
> > >          * the list of pending reports and also add these to the
> > >          * accept list if there is still space. Abort if space runs o=
ut.
> > >          */
> > > -       list_for_each_entry(params, &hdev->pend_le_reports, action) {
> > > -               err =3D hci_le_add_accept_list_sync(hdev, params, &nu=
m_entries);
> > > +
> > > +       conn_params_iter_init(&hdev->pend_le_reports);
> > > +
> > > +       while (conn_params_iter_next(&hdev->pend_le_reports, &params)=
) {
> > > +               hci_dev_unlock(hdev);
> > > +               err =3D hci_le_add_accept_list_sync(hdev, &params, &n=
um_entries);
> > >                 if (err)
> > >                         goto done;
> > > +               hci_dev_lock(hdev);
> > >         }
> > >
> > > +       hci_dev_unlock(hdev);
> > > +
> > >         /* Use the allowlist unless the following conditions are all =
true:
> > >          * - We are not currently suspending
> > >          * - There are 1 or more ADV monitors registered and it's not=
 offloaded
> > > --
> > > 2.40.1
> > >
> >
> >
>


--=20
Luiz Augusto von Dentz