Re: [PATCH 1/3] Bluetooth: hci_sync: iterate over hci_conn_params safely

[Pauli Virtanen <pav@iki.fi>]

Hi Luiz,

pe, 2023-06-09 kello 10:19 -0700, Luiz Augusto von Dentz kirjoitti:
> On Thu, Jun 8, 2023 at 2:10 PM Pauli Virtanen <pav@iki.fi> wrote:
> > 
> > hci_update_accept_list_sync iterates over hdev->pend_le_conns and
> > hdev->pend_le_reports, and waits for controller events in the loop body,
> > 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:
> > 
> > ==================================================================
> > 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_sync.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.fc38 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/mmzone.h:2011 arch/x86/mm/physaddr.c:65)
> > ? hci_update_passive_scan_sync (net/bluetooth/hci_sync.c:2536 net/bluetooth/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/bluetooth/hci_sync.c:2723 net/bluetooth/hci_sync.c:2841)
> > hci_update_passive_scan_sync (net/bluetooth/hci_sync.c:2536 net/bluetooth/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/workqueue.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/kasan/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/workqueue.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)
> > ==================================================================
> > 
> > Fixes: e8907f76544f ("Bluetooth: hci_sync: Make use of hci_cmd_sync_queue set 3")
> > Signed-off-by: Pauli Virtanen <pav@iki.fi>
> > ---
> > 
> > Notes:
> >     It might be that even more of hci_passive_scan_sync and the routines 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 *params)
> > +                                       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 = HCI_NETWORK_PRIVACY;
> > 
> > +       hci_dev_lock(hdev);
> > +       hparams = hci_conn_params_lookup(hdev, &params->addr,
> > +                                        params->addr_type);
> > +       if (hparams)
> > +               hparams->privacy_mode = 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 *params)
> > +                                       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(struct hci_dev *hdev,
> >         return __hci_cmd_sync_sk(hdev, opcode, 0, NULL, 0, HCI_CMD_TIMEOUT, 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 = 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 allowed. */
> > +
> > +       list_for_each_entry(params, list, action) {
> > +               if (!params->add_pending)
> > +                       continue;
> > +
> > +               memcpy(&item->addr, &params->addr, sizeof(params->addr));
> > +               item->addr_type = params->addr_type;
> > +               item->privacy_mode = params->privacy_mode;
> > +               item->flags = params->flags;
> > +
> > +               params->add_pending = 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).


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.


> >  /* 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(struct 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 = 0;
> >         bool pend_conn, pend_report;
> > @@ -2494,6 +2540,8 @@ static u8 hci_update_accept_list_sync(struct hci_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 connected or is
> >          * still in the list of pending connections or list of devices to
> > @@ -2515,8 +2563,10 @@ static u8 hci_update_accept_list_sync(struct hci_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 = hci_le_add_accept_list_sync(hdev, params, &num_entries);
> > +
> > +       conn_params_iter_init(&hdev->pend_le_conns);
> > +
> > +       while (conn_params_iter_next(&hdev->pend_le_conns, &params)) {
> > +               hci_dev_unlock(hdev);
> > +               err = hci_le_add_accept_list_sync(hdev, &params, &num_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 out.
> >          */
> > -       list_for_each_entry(params, &hdev->pend_le_reports, action) {
> > -               err = hci_le_add_accept_list_sync(hdev, params, &num_entries);
> > +
> > +       conn_params_iter_init(&hdev->pend_le_reports);
> > +
> > +       while (conn_params_iter_next(&hdev->pend_le_reports, &params)) {
> > +               hci_dev_unlock(hdev);
> > +               err = hci_le_add_accept_list_sync(hdev, &params, &num_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
> > 
> 
>