by Luiz Augusto von Dentz

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Subject: Re: [PATCH v2 1/3] Bluetooth: use RCU for hci_conn_params and iterate safely in hci_sync

Hi Pauli,

On Thu, Jun 15, 2023 at 1:10 PM Pauli Virtanen <[email protected]> wrote:
>
> Hi Luiz,
>
> ke, 2023-06-14 kello 09:19 -0700, Luiz Augusto von Dentz kirjoitti:
> > Hi Pauli,
> >
> > On Tue, Jun 13, 2023 at 4:07 PM Pauli Virtanen <[email protected]> wrote:
> > >
> > > Hi Luiz,
> > >
> > > ti, 2023-06-13 kello 12:38 -0700, Luiz Augusto von Dentz kirjoitti:
> > > > Hi Pauli,
> > > >
> > > > On Tue, Jun 13, 2023 at 12:04 PM Luiz Augusto von Dentz
> > > > <[email protected]> wrote:
> > > > >
> > > > > Hi Pauli,
> > > > >
> > > > > On Tue, Jun 13, 2023 at 11:17 AM Pauli Virtanen <[email protected]> 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).
> > > > > >
> > > > > > Use RCU for the hci_conn_params action lists. Since the loop bodies in
> > > > > > hci_sync block and we cannot use RCU for the whole loop, add
> > > > > > hci_conn_params.add_pending to keep track which items are left. Copy
> > > > > > data to avoid needing lock on hci_conn_params. Only the flags field is
> > > > > > written from elsewhere, so READ_ONCE/WRITE_ONCE should guarantee we read
> > > > > > valid values.
> > > > > >
> > > > > > Free params everywhere with hci_conn_params_free so the cleanup is
> > > > > > guaranteed to be done properly.
> > > > > >
> > > > > > 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 <[email protected]>
> > > > > > ---
> > > > > >
> > > > > > Notes:
> > > > > > v2: use RCU
> > > > >
> > > > > Really nice work.
> > > > >
> > > > > > include/net/bluetooth/hci_core.h | 5 ++
> > > > > > net/bluetooth/hci_conn.c | 9 ++--
> > > > > > net/bluetooth/hci_core.c | 34 +++++++++---
> > > > > > net/bluetooth/hci_event.c | 12 ++---
> > > > > > net/bluetooth/hci_sync.c | 93 ++++++++++++++++++++++++++++----
> > > > > > net/bluetooth/mgmt.c | 30 +++++------
> > > > > > 6 files changed, 141 insertions(+), 42 deletions(-)
> > > > > >
> > > > > > diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
> > > > > > index 683666ea210c..8c6ac6d29c62 100644
> > > > > > --- a/include/net/bluetooth/hci_core.h
> > > > > > +++ b/include/net/bluetooth/hci_core.h
> > > > > > @@ -822,6 +822,8 @@ struct hci_conn_params {
> > > > > >
> > > > > > struct hci_conn *conn;
> > > > > > bool explicit_connect;
> > > > > > + /* Accessed without hdev->lock: */
> > > > > > + bool add_pending;
> > > > >
> > > > > That is the only part that Im a little uncorfortable with, are we
> > > > > doing this because we can't do use the cmd_sync while holding RCU
> > > > > lock? In that case couldn't we perhaps update the list? Also we could
> > > > > perhaps add it as a flag rather than a separated field.
> > >
> > > Yes, it is because we have to release the rcu read lock while doing
> > > __hci_cmd_sync_sk, and when we'd like to re-lock to continue the
> > > iteration we can't know if the current pointer we have is still valid
> > > and points to the same object (also if same address appears in list it
> > > might be different object).
> > >
> > > At the moment I'm not seeing how to iterate over this in principle
> > > arbitrarily mutating list, without either marking the list entries in
> > > one way or another in the iteration, or having some more lifetime
> > > guarantees for them.
> > >
> > > The marker could be a flag, but would maybe need atomic ops if the flag
> > > field is written concurrently also from elsewhere if we want to be 100%
> > > sure...
> > >
> > > A problem with modifying the list (ie using action field to track
> > > iteration status) is that in other parts things are looked up with
> > > hci_pend_le_action_lookup so the items can't be moved away from it
> > > temporarily (which otherwise would probably work here).
> > >
> > > > > > hci_conn_flags_t flags;
> > > > > > u8 privacy_mode;
> > > > > > };
> > > > > > @@ -1605,6 +1607,9 @@ struct hci_conn_params *hci_conn_params_add(struct hci_dev *hdev,
> > > > > > bdaddr_t *addr, u8 addr_type);
> > > > > > void hci_conn_params_del(struct hci_dev *hdev, bdaddr_t *addr, u8 addr_type);
> > > > > > void hci_conn_params_clear_disabled(struct hci_dev *hdev);
> > > > > > +void hci_conn_params_free(struct hci_conn_params *param);
> > > > > > +void hci_conn_params_set_pending(struct hci_conn_params *param,
> > > > > > + struct list_head *list);
> > > > > >
> > > > > > struct hci_conn_params *hci_pend_le_action_lookup(struct list_head *list,
> > > > > > bdaddr_t *addr,
> > > > > > diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
> > > > > > index 7d4941e6dbdf..ae9a35d1405b 100644
> > > > > > --- a/net/bluetooth/hci_conn.c
> > > > > > +++ b/net/bluetooth/hci_conn.c
> > > > > > @@ -118,7 +118,7 @@ static void hci_connect_le_scan_cleanup(struct hci_conn *conn, u8 status)
> > > > > > */
> > > > > > params->explicit_connect = false;
> > > > > >
> > > > > > - list_del_init(&params->action);
> > > > > > + hci_conn_params_set_pending(params, NULL);
> > > > > >
> > > > > > switch (params->auto_connect) {
> > > > > > case HCI_AUTO_CONN_EXPLICIT:
> > > > > > @@ -127,10 +127,10 @@ static void hci_connect_le_scan_cleanup(struct hci_conn *conn, u8 status)
> > > > > > return;
> > > > > > case HCI_AUTO_CONN_DIRECT:
> > > > > > case HCI_AUTO_CONN_ALWAYS:
> > > > > > - list_add(&params->action, &hdev->pend_le_conns);
> > > > > > + hci_conn_params_set_pending(params, &hdev->pend_le_conns);
> > > > > > break;
> > > > > > case HCI_AUTO_CONN_REPORT:
> > > > > > - list_add(&params->action, &hdev->pend_le_reports);
> > > > > > + hci_conn_params_set_pending(params, &hdev->pend_le_reports);
> > > > > > break;
> > > > > > default:
> > > > > > break;
> > > > > > @@ -1435,8 +1435,7 @@ static int hci_explicit_conn_params_set(struct hci_dev *hdev,
> > > > > > if (params->auto_connect == HCI_AUTO_CONN_DISABLED ||
> > > > > > params->auto_connect == HCI_AUTO_CONN_REPORT ||
> > > > > > params->auto_connect == HCI_AUTO_CONN_EXPLICIT) {
> > > > > > - list_del_init(&params->action);
> > > > > > - list_add(&params->action, &hdev->pend_le_conns);
> > > > > > + hci_conn_params_set_pending(params, &hdev->pend_le_conns);
> > > > >
> > > > > Id just follow the name convention e.g. hci_conn_params_list_add,
> > > > > hci_conn_params_list_del, etc.
> > >
> > > Ok. hci_conn_params are also in the different hdev->le_conn_params
> > > list, maybe hci_pend_le_list_add, hci_pend_le_list_del_init
> > >
> > > > >
> > > > > > }
> > > > > >
> > > > > > params->explicit_connect = true;
> > > > > > diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
> > > > > > index 48917c68358d..7992a61fe1fd 100644
> > > > > > --- a/net/bluetooth/hci_core.c
> > > > > > +++ b/net/bluetooth/hci_core.c
> > > > > > @@ -2249,21 +2249,41 @@ struct hci_conn_params *hci_conn_params_lookup(struct hci_dev *hdev,
> > > > > > return NULL;
> > > > > > }
> > > > > >
> > > > > > -/* This function requires the caller holds hdev->lock */
> > > > > > +/* This function requires the caller holds hdev->lock or rcu_read_lock */
> > > > > > struct hci_conn_params *hci_pend_le_action_lookup(struct list_head *list,
> > > > > > bdaddr_t *addr, u8 addr_type)
> > > > > > {
> > > > > > struct hci_conn_params *param;
> > > > > >
> > > > > > - list_for_each_entry(param, list, action) {
> > > > > > + rcu_read_lock();
> > > > > > +
> > > > > > + list_for_each_entry_rcu(param, list, action) {
> > > > > > if (bacmp(&param->addr, addr) == 0 &&
> > > > > > - param->addr_type == addr_type)
> > > > > > + param->addr_type == addr_type) {
> > > > > > + rcu_read_unlock();
> > > > > > return param;
> > > > > > + }
> > > > > > }
> > > > > >
> > > > > > + rcu_read_unlock();
> > > > > > +
> > > > > > return NULL;
> > > > > > }
> > > > > >
> > > > > > +/* This function requires the caller holds hdev->lock */
> > > > > > +void hci_conn_params_set_pending(struct hci_conn_params *param,
> > > > > > + struct list_head *list)
> > > > > > +{
> > > > > > + if (!list_empty(&param->action)) {
> > > > > > + list_del_rcu(&param->action);
> > > > > > + synchronize_rcu();
> > > > > > + INIT_LIST_HEAD(&param->action);
> > > > > > + }
> > > > > > +
> > > > > > + if (list)
> > > > > > + list_add_rcu(&param->action, list);
> > > > > > +}
> > > > > > +
> > > > > > /* This function requires the caller holds hdev->lock */
> > > > > > struct hci_conn_params *hci_conn_params_add(struct hci_dev *hdev,
> > > > > > bdaddr_t *addr, u8 addr_type)
> > > > > > @@ -2297,14 +2317,15 @@ struct hci_conn_params *hci_conn_params_add(struct hci_dev *hdev,
> > > > > > return params;
> > > > > > }
> > > > > >
> > > > > > -static void hci_conn_params_free(struct hci_conn_params *params)
> > > > > > +void hci_conn_params_free(struct hci_conn_params *params)
> > > > > > {
> > > > > > + hci_conn_params_set_pending(params, NULL);
> > > > > > +
> > > > > > if (params->conn) {
> > > > > > hci_conn_drop(params->conn);
> > > > > > hci_conn_put(params->conn);
> > > > > > }
> > > > > >
> > > > > > - list_del(&params->action);
> > > > > > list_del(&params->list);
> > > > > > kfree(params);
> > > > > > }
> > > > > > @@ -2342,8 +2363,7 @@ void hci_conn_params_clear_disabled(struct hci_dev *hdev)
> > > > > > continue;
> > > > > > }
> > > > > >
> > > > > > - list_del(&params->list);
> > > > > > - kfree(params);
> > > > > > + hci_conn_params_free(params);
> > > > > > }
> > > > > >
> > > > > > BT_DBG("All LE disabled connection parameters were removed");
> > > > > > diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> > > > > > index 7c199f7361f7..8187c9f827fa 100644
> > > > > > --- a/net/bluetooth/hci_event.c
> > > > > > +++ b/net/bluetooth/hci_event.c
> > > > > > @@ -1564,7 +1564,7 @@ static u8 hci_cc_le_set_privacy_mode(struct hci_dev *hdev, void *data,
> > > > > >
> > > > > > params = hci_conn_params_lookup(hdev, &cp->bdaddr, cp->bdaddr_type);
> > > > > > if (params)
> > > > > > - params->privacy_mode = cp->mode;
> > > > > > + WRITE_ONCE(params->privacy_mode, cp->mode);
> > > > > >
> > > > > > hci_dev_unlock(hdev);
> > > > > >
> > > > > > @@ -2804,8 +2804,8 @@ static void hci_cs_disconnect(struct hci_dev *hdev, u8 status)
> > > > > >
> > > > > > case HCI_AUTO_CONN_DIRECT:
> > > > > > case HCI_AUTO_CONN_ALWAYS:
> > > > > > - list_del_init(&params->action);
> > > > > > - list_add(&params->action, &hdev->pend_le_conns);
> > > > > > + hci_conn_params_set_pending(params,
> > > > > > + &hdev->pend_le_conns);
> > > > > > break;
> > > > > >
> > > > > > default:
> > > > > > @@ -3423,8 +3423,8 @@ static void hci_disconn_complete_evt(struct hci_dev *hdev, void *data,
> > > > > >
> > > > > > case HCI_AUTO_CONN_DIRECT:
> > > > > > case HCI_AUTO_CONN_ALWAYS:
> > > > > > - list_del_init(&params->action);
> > > > > > - list_add(&params->action, &hdev->pend_le_conns);
> > > > > > + hci_conn_params_set_pending(params,
> > > > > > + &hdev->pend_le_conns);
> > > > > > hci_update_passive_scan(hdev);
> > > > > > break;
> > > > > >
> > > > > > @@ -5972,7 +5972,7 @@ static void le_conn_complete_evt(struct hci_dev *hdev, u8 status,
> > > > > > params = hci_pend_le_action_lookup(&hdev->pend_le_conns, &conn->dst,
> > > > > > conn->dst_type);
> > > > > > if (params) {
> > > > > > - list_del_init(&params->action);
> > > > > > + hci_conn_params_set_pending(params, NULL);
> > > > > > if (params->conn) {
> > > > > > hci_conn_drop(params->conn);
> > > > > > hci_conn_put(params->conn);
> > > > > > diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
> > > > > > index 97da5bcaa904..da12e286ee64 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 *p;
> > > > > >
> > > > > > if (!use_ll_privacy(hdev))
> > > > > > return 0;
> > > > > > @@ -2203,6 +2211,16 @@ static int hci_le_add_resolve_list_sync(struct hci_dev *hdev,
> > > > > > /* Default privacy mode is always Network */
> > > > > > params->privacy_mode = HCI_NETWORK_PRIVACY;
> > > > > >
> > > > > > + rcu_read_lock();
> > > > > > + p = hci_pend_le_action_lookup(&hdev->pend_le_conns,
> > > > > > + &params->addr, params->addr_type);
> > > > > > + if (!p)
> > > > > > + p = hci_pend_le_action_lookup(&hdev->pend_le_reports,
> > > > > > + &params->addr, params->addr_type);
> > > > > > + if (p)
> > > > > > + WRITE_ONCE(p->privacy_mode, HCI_NETWORK_PRIVACY);
> > > > > > + rcu_read_unlock();
> > > > > > +
> > > > > > done:
> > > > > > if (hci_dev_test_flag(hdev, HCI_PRIVACY))
> > > > > > memcpy(cp.local_irk, hdev->irk, 16);
> > > > > > @@ -2215,7 +2233,7 @@ 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;
> > > > > > @@ -2240,6 +2258,8 @@ static int hci_le_set_privacy_mode_sync(struct hci_dev *hdev,
> > > > > > bacpy(&cp.bdaddr, &irk->bdaddr);
> > > > > > cp.mode = HCI_DEVICE_PRIVACY;
> > > > > >
> > > > > > + /* Note: params->privacy_mode is not updated since it is a copy */
> > > > > > +
> > > > > > return __hci_cmd_sync_status(hdev, HCI_OP_LE_SET_PRIVACY_MODE,
> > > > > > sizeof(cp), &cp, HCI_CMD_TIMEOUT);
> > > > > > }
> > > > > > @@ -2249,7 +2269,7 @@ 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 +2467,51 @@ 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_add_iter_init(struct list_head *list)
> > > > > > +{
> > > > > > + struct hci_conn_params *params;
> > > > > > +
> > > > > > + rcu_read_lock();
> > > > > > +
> > > > > > + list_for_each_entry_rcu(params, list, action)
> > > > > > + params->add_pending = true;
> > > > > > +
> > > > > > + rcu_read_unlock();
> > > > > > +}
> > > > > > +
> > > > > > +static bool conn_params_add_iter_next(struct list_head *list,
> > > > > > + struct conn_params *item)
> > > > > > +{
> > > > > > + struct hci_conn_params *params;
> > > > > > +
> > > > > > + rcu_read_lock();
> > > > > > +
> > > > > > + list_for_each_entry_rcu(params, list, action) {
> > > > > > + if (!params->add_pending)
> > > > > > + continue;
> > > > > > +
> > > > > > + /* No hdev->lock, but: addr, addr_type are immutable.
> > > > > > + * privacy_mode is only written by us or in
> > > > > > + * hci_cc_le_set_privacy_mode that we wait for.
> > > > > > + * We should be idempotent so MGMT updating flags
> > > > > > + * while we are processing is OK.
> > > > > > + */
> > > > > > + bacpy(&item->addr, &params->addr);
> > > > > > + item->addr_type = params->addr_type;
> > > > > > + item->flags = READ_ONCE(params->flags);
> > > > > > + item->privacy_mode = READ_ONCE(params->privacy_mode);
> > > > > > +
> > > > > > + params->add_pending = false;
> > > > > > +
> > > > > > + rcu_read_unlock();
> > > > > > + return true;
> > > > > > + }
> > > > > > +
> > > > > > + rcu_read_unlock();
> > > > > > +
> > > > > > + return false;
> > > > > > +}
> > > > > > +
> > > > > > /* Device must not be scanning when updating the accept list.
> > > > > > *
> > > > > > * Update is done using the following sequence:
> > > > > > @@ -2466,7 +2531,7 @@ 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;
> > > > > > @@ -2504,6 +2569,7 @@ static u8 hci_update_accept_list_sync(struct hci_dev *hdev)
> > > > > > if (hci_conn_hash_lookup_le(hdev, &b->bdaddr, b->bdaddr_type))
> > > > > > continue;
> > > > > >
> > > > > > + /* Pointers not dereferenced, no locks needed */
> > > > > > pend_conn = hci_pend_le_action_lookup(&hdev->pend_le_conns,
> > > > > > &b->bdaddr,
> > > > > > b->bdaddr_type);
> > > > > > @@ -2532,9 +2598,15 @@ 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 and params may be mutated while we wait for events,
> > > > > > + * 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_add_iter_init(&hdev->pend_le_conns);
> > > > > > +
> > > > > > + while (conn_params_add_iter_next(&hdev->pend_le_conns, &params)) {
> > > > > > + err = hci_le_add_accept_list_sync(hdev, &params, &num_entries);
> > > > > > if (err)
> > > > > > goto done;
> > > >
> > > > Perhaps we should be using list_for_each_entry_continue_rcu instead of
> > > > creating our own version of it? Or at least use it internally on
> > > > iter_next, anyway I think what we are after is some way to do
> > > > rcu_unlock add_to_list rcu_lock on a loop.
> > >
> > > I think list_for_each_entry_continue_rcu differs from
> > > list_for_each_entry_rcu in that it doesn't start from the list head.
> > >
> > > IIUC it requires starting from a valid list entry, and needs holding
> > > the rcu read lock all the time, to ensure it is not invalidated. If so,
> > > it seems it can't be used here since we need to release the lock and
> > > the cursor might be gone before we re-lock.
> >
> > I wonder if we can have something similar to for_each_safe version
> > under rcu_lock then or perhaps there is a problem with the whole list
> > getting freed in the meantime? It is perhaps a good idea to introduce
> > some test to cover this in iso-tester so we make sure we don't
> > reintroduce it this sort of problem in the future.
>
> Any element of the list can in principle get freed while we wait for
> controller to reply. The *_safe iterator guards against freeing the
> current element, but if it's the next element that gets freed it
> crashes too.
>
> If we want alternatives, making a copy of all items in the list under
> rcu lock and then releasing and iterating over the copied list would
> work. Or we could add refcount or some other "don't free me yet" flag
> to the params (but we might want to make a copy still to ensure the
> flags aren't changed under us).
>
> I sent a patch adding a reproducer to mgmt-tester.c. There's maybe more
> ways that you can hit it with enough bad luck (or emulator timing
> help).

I guess we shall just do the local copy then, we anyway iterate over
the list a couple of times, doing one extra loop shouldn't make it
much worse beside with the current version is probably worst in this
respect.

>
> > > > > > }
> > > > > > @@ -2543,8 +2615,11 @@ static u8 hci_update_accept_list_sync(struct hci_dev *hdev)
> > > > > > * 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_add_iter_init(&hdev->pend_le_reports);
> > > > > > +
> > > > > > + while (conn_params_add_iter_next(&hdev->pend_le_reports, &params)) {
> > > > > > + err = hci_le_add_accept_list_sync(hdev, &params, &num_entries);
> > > > > > if (err)
> > > > > > goto done;
> > > > > > }
> > > > > > @@ -4837,12 +4912,12 @@ static void hci_pend_le_actions_clear(struct hci_dev *hdev)
> > > > > > struct hci_conn_params *p;
> > > > > >
> > > > > > list_for_each_entry(p, &hdev->le_conn_params, list) {
> > > > > > + hci_conn_params_set_pending(p, NULL);
> > > > > > if (p->conn) {
> > > > > > hci_conn_drop(p->conn);
> > > > > > hci_conn_put(p->conn);
> > > > > > p->conn = NULL;
> > > > > > }
> > > > > > - list_del_init(&p->action);
> > > > > > }
> > > > > >
> > > > > > BT_DBG("All LE pending actions cleared");
> > > > > > diff --git a/net/bluetooth/mgmt.c b/net/bluetooth/mgmt.c
> > > > > > index 61c8e1b8f3b0..b35b1c685b86 100644
> > > > > > --- a/net/bluetooth/mgmt.c
> > > > > > +++ b/net/bluetooth/mgmt.c
> > > > > > @@ -1303,15 +1303,15 @@ static void restart_le_actions(struct hci_dev *hdev)
> > > > > > /* Needed for AUTO_OFF case where might not "really"
> > > > > > * have been powered off.
> > > > > > */
> > > > > > - list_del_init(&p->action);
> > > > > > + hci_conn_params_set_pending(p, NULL);
> > > > > >
> > > > > > switch (p->auto_connect) {
> > > > > > case HCI_AUTO_CONN_DIRECT:
> > > > > > case HCI_AUTO_CONN_ALWAYS:
> > > > > > - list_add(&p->action, &hdev->pend_le_conns);
> > > > > > + hci_conn_params_set_pending(p, &hdev->pend_le_conns);
> > > > > > break;
> > > > > > case HCI_AUTO_CONN_REPORT:
> > > > > > - list_add(&p->action, &hdev->pend_le_reports);
> > > > > > + hci_conn_params_set_pending(p, &hdev->pend_le_reports);
> > > > > > break;
> > > > > > default:
> > > > > > break;
> > > > > > @@ -5175,7 +5175,7 @@ static int set_device_flags(struct sock *sk, struct hci_dev *hdev, void *data,
> > > > > > goto unlock;
> > > > > > }
> > > > > >
> > > > > > - params->flags = current_flags;
> > > > > > + WRITE_ONCE(params->flags, current_flags);
> > > > > > status = MGMT_STATUS_SUCCESS;
> > > > > >
> > > > > > /* Update passive scan if HCI_CONN_FLAG_DEVICE_PRIVACY
> > > > > > @@ -7586,7 +7586,7 @@ static int hci_conn_params_set(struct hci_dev *hdev, bdaddr_t *addr,
> > > > > > if (params->auto_connect == auto_connect)
> > > > > > return 0;
> > > > > >
> > > > > > - list_del_init(&params->action);
> > > > > > + hci_conn_params_set_pending(params, NULL);
> > > > > >
> > > > > > switch (auto_connect) {
> > > > > > case HCI_AUTO_CONN_DISABLED:
> > > > > > @@ -7595,18 +7595,22 @@ static int hci_conn_params_set(struct hci_dev *hdev, bdaddr_t *addr,
> > > > > > * connect to device, keep connecting.
> > > > > > */
> > > > > > if (params->explicit_connect)
> > > > > > - list_add(&params->action, &hdev->pend_le_conns);
> > > > > > + hci_conn_params_set_pending(params,
> > > > > > + &hdev->pend_le_conns);
> > > > > > break;
> > > > > > case HCI_AUTO_CONN_REPORT:
> > > > > > if (params->explicit_connect)
> > > > > > - list_add(&params->action, &hdev->pend_le_conns);
> > > > > > + hci_conn_params_set_pending(params,
> > > > > > + &hdev->pend_le_conns);
> > > > > > else
> > > > > > - list_add(&params->action, &hdev->pend_le_reports);
> > > > > > + hci_conn_params_set_pending(params,
> > > > > > + &hdev->pend_le_reports);
> > > > > > break;
> > > > > > case HCI_AUTO_CONN_DIRECT:
> > > > > > case HCI_AUTO_CONN_ALWAYS:
> > > > > > if (!is_connected(hdev, addr, addr_type))
> > > > > > - list_add(&params->action, &hdev->pend_le_conns);
> > > > > > + hci_conn_params_set_pending(params,
> > > > > > + &hdev->pend_le_conns);
> > > > > > break;
> > > > > > }
> > > > > >
> > > > > > @@ -7829,9 +7833,7 @@ static int remove_device(struct sock *sk, struct hci_dev *hdev,
> > > > > > goto unlock;
> > > > > > }
> > > > > >
> > > > > > - list_del(&params->action);
> > > > > > - list_del(&params->list);
> > > > > > - kfree(params);
> > > > > > + hci_conn_params_free(params);
> > > > > >
> > > > > > device_removed(sk, hdev, &cp->addr.bdaddr, cp->addr.type);
> > > > > > } else {
> > > > > > @@ -7862,9 +7864,7 @@ static int remove_device(struct sock *sk, struct hci_dev *hdev,
> > > > > > p->auto_connect = HCI_AUTO_CONN_EXPLICIT;
> > > > > > continue;
> > > > > > }
> > > > > > - list_del(&p->action);
> > > > > > - list_del(&p->list);
> > > > > > - kfree(p);
> > > > > > + hci_conn_params_free(p);
> > > > > > }
> > > > > >
> > > > > > bt_dev_dbg(hdev, "All LE connection parameters were removed");
> > > > > > --
> > > > > > 2.40.1
> > > > > >
> > > > >
> > > > >
> > > > > --
> > > > > Luiz Augusto von Dentz
> > > >
> > > >
> > > >
> > >
> >
> >
>

--
Luiz Augusto von Dentz