[PATCH v2 0/2] Bluetooth: SMP: Serialize root channel updates

[PATCH v2 0/2] Bluetooth: SMP: Serialize root channel updates

[Cen Zhang]

The SMP root channels in hdev->smp_data and hdev->smp_bredr_data are
used by HCI event processing under hdev->lock and by SMP receive
callbacks on hdev->workqueue. Power-off already removes them under
hdev->lock in hci_dev_close_sync(). Two other writers do not serialize
with these users:

  1/2 The force_bredr_smp debugfs switch creates and removes the BR/EDR
      root without hdev->lock. A connection confirmation can see a root
      whose operations are not set yet, and a disable can race with
      power-off and release the channel twice. Take hdev->lock in the
      writer, and skip the deletion when power-off already emptied the
      slot.

  2/2 smp_register() replaces both roots when management powers on a
      controller that is already up with HCI_AUTO_OFF set, while HCI
      event processing and SMP receive callbacks can still be using the
      old roots. Run the registration on hdev->workqueue, where it ran
      before commit 2ff13894cfb8 ("Bluetooth: Perform HCI update for
      power on synchronously"), and hold hdev->lock while it replaces
      the roots. The caller waits for the work without holding
      hdev->lock, which HCI event processing on that workqueue takes.

smp_register() still warns when it replaces the channels on that path.
This series only makes the replacement safe.

Cen Zhang (2):
  Bluetooth: SMP: Serialize forced BR/EDR channel changes
  Bluetooth: SMP: Serialize root channel replacement

 net/bluetooth/hci_debugfs.c |  2 ++
 net/bluetooth/smp.c         | 38 +++++++++++++++++++++++++++++++++++--
 net/bluetooth/smp.h         |  3 ++-
 3 files changed, 40 insertions(+), 3 deletions(-)

---
Changes in v2:
- Address the CheckPatch and GitLint long-line failures reported by the
  Bluetooth CI: https://patchwork.kernel.org/series/1197223/
- Trim the crash reports in both commit messages to the headline, call trace
  and allocation/free stacks; no code changes.

Link to v1: https://lore.kernel.org/r/pm-bluetooth-objects-candidate-0184-v7-c26e53b52c260063ab6a-0@gmail.com

[PATCH v2 1/2] Bluetooth: SMP: Serialize forced BR/EDR channel changes

[Cen Zhang]

The force_bredr_smp debugfs switch creates and removes the BR/EDR SMP
root channel in hdev->smp_bredr_data without holding hdev->lock. The
other users of that channel hold the lock: l2cap_connect_cfm() looks up
fixed channels during HCI event processing, and hci_dev_close_sync()
removes the root through smp_unregister().

Enabling the switch can let a connection confirmation use a root that
is not fully initialized. smp_add_cid() publishes the channel through
l2cap_chan_create() and sets BT_LISTEN before it assigns the channel
operations and the parent lock nesting level:

  Debugfs writer                  HCI receive worker
  smp_add_cid()
    l2cap_chan_create()
    l2cap_add_scid()
    chan->state = BT_LISTEN
                                  hci_dev_lock(hdev)
                                  l2cap_connect_cfm()
                                    l2cap_global_fixed_chan()
                                    l2cap_chan_lock(root)
                                    l2cap_new_connection()
                                      root->ops->new_connection()
    chan->ops = &smp_root_chan_ops

Disabling the switch can race with power-off, which releases the same
channel:

  Debugfs writer                  Power-off
  smp_force_bredr(hdev, false)
    chan = hdev->smp_bredr_data
                                  hci_dev_lock(hdev)
                                  smp_unregister(hdev)
                                    smp_del_chan(chan), chan is freed
                                  hci_dev_unlock(hdev)
    smp_del_chan(chan)
      reads chan->data after the free

Hold hdev->lock around smp_force_bredr() in the debugfs writer and
annotate that requirement. smp_unregister() leaves HCI_FORCE_BREDR_SMP
set, so after power-off the slot is empty while the switch still reads
as enabled. Disabling it then passes NULL to smp_del_chan() even without
a race; skip the deletion in that case and only clear the flag.

Both reports below come from test kernels with scheduling hooks that
widen these windows. In the enable case lockdep also reported recursive
locking just before the oops, because the root still had the default
nesting level.

Oops report as below:

    Oops: general protection fault, probably for non-canonical address
    0xdffffc0000000001: 0000 [#1] SMP KASAN NOPTI
    KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
    Workqueue: hci1 hci_rx_work
    RIP: 0010:l2cap_new_connection+0x16c/0x320
    Call Trace:
     <TASK>
     l2cap_connect_cfm+0x46c/0xe60
     hci_remote_ext_features_evt+0x67d/0xbd0
     hci_event_packet+0x894/0xc70
     hci_rx_work+0x367/0xf00
     process_one_work+0x908/0x19c0
     worker_thread+0x65c/0xe40
     kthread+0x34f/0x460
     ret_from_fork+0x659/0x940
     ret_from_fork_asm+0x1a/0x30
     </TASK>

KASAN report as below:

    ==================================================================
    BUG: KASAN: slab-use-after-free in smp_del_chan+0xd2/0xe0
    Read of size 8 at addr ffff888112a2e4a0 by task sh/493

    Call Trace:
     <TASK>
     dump_stack_lvl+0x93/0xd0
     print_report+0xce/0x630
     kasan_report+0xe0/0x110
     smp_del_chan+0xd2/0xe0
     smp_force_bredr+0xda/0x200
     force_bredr_smp_write+0xc9/0x130
     full_proxy_write+0x11f/0x180
     vfs_write+0x25a/0x1010
     ksys_write+0x111/0x200
     do_syscall_64+0x115/0x6a0
     entry_SYSCALL_64_after_hwframe+0x77/0x7f
     </TASK>

    Allocated by task 493:
     kasan_save_stack+0x33/0x60
     kasan_save_track+0x14/0x30
     __kasan_kmalloc+0xaa/0xb0
     __kmalloc_cache_noprof+0x251/0x610
     l2cap_chan_create+0x47/0x930
     smp_add_cid+0x309/0x4f0
     smp_force_bredr+0x17d/0x200
     force_bredr_smp_write+0xc9/0x130
     full_proxy_write+0x11f/0x180
     vfs_write+0x25a/0x1010
     ksys_write+0x111/0x200
     do_syscall_64+0x115/0x6a0
     entry_SYSCALL_64_after_hwframe+0x77/0x7f

    Freed by task 496:
     kasan_save_stack+0x33/0x60
     kasan_save_track+0x14/0x30
     kasan_save_free_info+0x3b/0x60
     __kasan_slab_free+0x5f/0x80
     kfree+0x307/0x580
     l2cap_chan_put+0x273/0x3a0
     smp_unregister+0x59/0xe0
     hci_dev_close_sync+0x4c9/0x1150
     hci_set_powered_sync+0x4a7/0x680
     set_powered_sync+0xaa/0x150
     hci_cmd_sync_work+0x1b3/0x450
     process_one_work+0x908/0x19c0
     worker_thread+0x65c/0xe40
     kthread+0x34f/0x460
     ret_from_fork+0x659/0x940
     ret_from_fork_asm+0x1a/0x30

    The buggy address belongs to the object at ffff888112a2e000
     which belongs to the cache kmalloc-2k of size 2048
    The buggy address is located 1184 bytes inside of
     freed 2048-byte region [ffff888112a2e000, ffff888112a2e800)
    ==================================================================

Fixes: 300acfdec916 ("Bluetooth: Introduce force_bredr_smp debugfs option for testing")
Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
---
Assisted-by: LLM

 net/bluetooth/hci_debugfs.c | 2 ++
 net/bluetooth/smp.c         | 2 +-
 net/bluetooth/smp.h         | 3 ++-
 3 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/hci_debugfs.c b/net/bluetooth/hci_debugfs.c
index cd5ef398f2382..f513731053d28 100644
--- a/net/bluetooth/hci_debugfs.c
+++ b/net/bluetooth/hci_debugfs.c
@@ -525,7 +525,9 @@ static ssize_t force_bredr_smp_write(struct file *file,
 	if (err)
 		return err;
 
+	hci_dev_lock(hdev);
 	err = smp_force_bredr(hdev, enable);
+	hci_dev_unlock(hdev);
 	if (err)
 		return err;
 
diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index 984b2d0b5e3e9..0e442cc2a35da 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -3356,7 +3356,7 @@ int smp_force_bredr(struct hci_dev *hdev, bool enable)
 			return PTR_ERR(chan);
 
 		hdev->smp_bredr_data = chan;
-	} else {
+	} else if (hdev->smp_bredr_data) {
 		struct l2cap_chan *chan;
 
 		chan = hdev->smp_bredr_data;
diff --git a/net/bluetooth/smp.h b/net/bluetooth/smp.h
index c86c463890078..13fe40c0cb244 100644
--- a/net/bluetooth/smp.h
+++ b/net/bluetooth/smp.h
@@ -193,7 +193,8 @@ bool smp_irk_matches(struct hci_dev *hdev, const u8 irk[16],
 int smp_generate_rpa(struct hci_dev *hdev, const u8 irk[16], bdaddr_t *rpa);
 int smp_generate_oob(struct hci_dev *hdev, u8 hash[16], u8 rand[16]);
 
-int smp_force_bredr(struct hci_dev *hdev, bool enable);
+int smp_force_bredr(struct hci_dev *hdev, bool enable)
+	__must_hold(&hdev->lock);
 
 int smp_register(struct hci_dev *hdev);
 void smp_unregister(struct hci_dev *hdev);

[PATCH v2 2/2] Bluetooth: SMP: Serialize root channel replacement

[Cen Zhang]

smp_register() replaces the SMP root channels when they are still
registered from an earlier power-on. This happens when management
powers on a controller that is already up with HCI_AUTO_OFF set:
hci_power_on_sync() clears the flag and runs hci_powered_update_sync()
again, which registers SMP so that the channels use the identity address
chosen for this power-on. The WARN_ON() in smp_register() fires on this
path, and the old channels and their SMP data are freed while two kinds
of users can still hold them.

HCI event handlers read hdev->smp_data under hdev->lock, for example
smp_irk_matches() when resolving the target of a directed advertising
report:

  HCI receive worker              Power-on request
  hci_dev_lock(hdev)
  smp_irk_matches()
    chan = hdev->smp_data
                                  hci_powered_update_sync()
                                    smp_register()
                                      smp_del_chan(chan), chan freed
    reads chan->data

SMP receive callbacks run on hdev->workqueue without hdev->lock and use
the ECDH transform of the root, for example smp_cmd_public_key():

  HCI receive worker (SMP)        Power-on request
  smp_cmd_public_key()
    tfm = root's tfm_ecdh
                                  smp_register()
                                    smp_del_chan()
                                      crypto_free_kpp(tfm)
    compute_ecdh_secret(tfm, ...)

Before commit 2ff13894cfb8 ("Bluetooth: Perform HCI update for power on
synchronously") moved it to the request worker, registration ran from the
completion callback of the power-on request in the HCI receive worker,
which serialized it with both users.

Run the registration on hdev->workqueue again and hold hdev->lock while
it replaces the channels. smp_register() waits for the work and returns
its result. Its callers hold the request lock but not hdev->lock, and no
work on hdev->workqueue takes the request lock; hci_dev_close_sync()
already drains this workqueue with the request lock held. Users that run
under the request lock, such as smp_generate_rpa(), stay serialized by
that lock.

The reports below come from test kernels with scheduling hooks that
widen these windows. The WARN_ON() in smp_register() was printed before
each of them.

KASAN report as below:

    ==================================================================
    BUG: KASAN: slab-use-after-free in smp_irk_matches+0x2fb/0x310
    Read of size 8 at addr ffff88810c35f4a0 by task kworker/u17:0/520

    Workqueue: hci0 hci_rx_work
    Call Trace:
     <TASK>
     dump_stack_lvl+0x93/0xd0
     print_report+0xce/0x630
     kasan_report+0xe0/0x110
     smp_irk_matches+0x2fb/0x310
     process_adv_report.part.0+0x2ce/0x1680
     hci_le_direct_adv_report_evt+0x2f8/0x4c0
     hci_le_meta_evt+0x30c/0x5c0
     hci_event_packet+0x4e8/0xc70
     hci_rx_work+0x367/0xf00
     process_one_work+0x908/0x19c0
     worker_thread+0x65c/0xe40
     kthread+0x34f/0x460
     ret_from_fork+0x659/0x940
     ret_from_fork_asm+0x1a/0x30
     </TASK>

    Allocated by task 522:
     kasan_save_stack+0x33/0x60
     kasan_save_track+0x14/0x30
     __kasan_kmalloc+0xaa/0xb0
     __kmalloc_cache_noprof+0x251/0x610
     l2cap_chan_create+0x47/0x930
     smp_add_cid+0x120/0x4f0
     smp_register+0xa7/0x400
     hci_powered_update_sync+0x88/0x720
     hci_dev_open_sync+0xae0/0x2060
     hci_set_powered_sync+0x2a9/0x720
     set_powered_sync+0xaa/0x150
     hci_cmd_sync_work+0x1b3/0x450
     process_one_work+0x908/0x19c0
     worker_thread+0x65c/0xe40
     kthread+0x34f/0x460
     ret_from_fork+0x659/0x940
     ret_from_fork_asm+0x1a/0x30

    Freed by task 522:
     kasan_save_stack+0x33/0x60
     kasan_save_track+0x14/0x30
     kasan_save_free_info+0x3b/0x60
     __kasan_slab_free+0x5f/0x80
     kfree+0x307/0x580
     l2cap_chan_put+0x273/0x3a0
     smp_del_chan+0x9f/0x170
     smp_register+0x2e8/0x400
     hci_powered_update_sync+0x88/0x720
     hci_set_powered_sync+0x5e5/0x720
     set_powered_sync+0xaa/0x150
     hci_cmd_sync_work+0x1b3/0x450
     process_one_work+0x908/0x19c0
     worker_thread+0x65c/0xe40
     kthread+0x34f/0x460
     ret_from_fork+0x659/0x940
     ret_from_fork_asm+0x1a/0x30

    The buggy address belongs to the object at ffff88810c35f000
     which belongs to the cache kmalloc-2k of size 2048
    The buggy address is located 1184 bytes inside of
     freed 2048-byte region [ffff88810c35f000, ffff88810c35f800)
    ==================================================================

KASAN report as below:

    ==================================================================
    BUG: KASAN: slab-use-after-free in compute_ecdh_secret+0x856/0xa50
    Read of size 4 at addr ffff8881071f4f00 by task kworker/u17:2/500

    Workqueue: hci1 hci_rx_work
    Call Trace:
     <TASK>
     dump_stack_lvl+0x93/0xd0
     print_report+0xce/0x630
     kasan_report+0xe0/0x110
     compute_ecdh_secret+0x856/0xa50
     smp_recv_cb+0x3acf/0x93b0
     l2cap_recv_frame+0x13cc/0x8830
     l2cap_recv_acldata+0xe9f/0x10e0
     hci_rx_work+0x5a6/0xf00
     process_one_work+0x908/0x19c0
     worker_thread+0x65c/0xe40
     kthread+0x34f/0x460
     ret_from_fork+0x659/0x940
     ret_from_fork_asm+0x1a/0x30
     </TASK>

    Allocated by task 497:
     kasan_save_stack+0x33/0x60
     kasan_save_track+0x14/0x30
     __kasan_kmalloc+0xaa/0xb0
     __kmalloc_node_noprof+0x2f2/0x7b0
     crypto_create_tfm_node+0x92/0x390
     crypto_alloc_tfm_node+0xf5/0x220
     smp_add_cid+0xc1/0x4f0
     smp_register+0x9d/0x430
     hci_powered_update_sync+0x82/0x680
     hci_set_powered_sync+0x4f4/0x750
     set_powered_sync+0xb8/0x210
     hci_cmd_sync_work+0x1b3/0x450
     process_one_work+0x908/0x19c0
     worker_thread+0x65c/0xe40
     kthread+0x34f/0x460
     ret_from_fork+0x659/0x940
     ret_from_fork_asm+0x1a/0x30

    Freed by task 497:
     kasan_save_stack+0x33/0x60
     kasan_save_track+0x14/0x30
     kasan_save_free_info+0x3b/0x60
     __kasan_slab_free+0x5f/0x80
     kfree+0x307/0x580
     crypto_destroy_tfm+0xdd/0x230
     smp_del_chan+0x8b/0x180
     smp_register+0x29d/0x430
     hci_powered_update_sync+0x82/0x680
     hci_set_powered_sync+0x4f4/0x750
     set_powered_sync+0xb8/0x210
     hci_cmd_sync_work+0x1b3/0x450
     process_one_work+0x908/0x19c0
     worker_thread+0x65c/0xe40
     kthread+0x34f/0x460
     ret_from_fork+0x659/0x940
     ret_from_fork_asm+0x1a/0x30

    The buggy address belongs to the object at ffff8881071f4f00
     which belongs to the cache kmalloc-128 of size 128
    The buggy address is located 0 bytes inside of
     freed 128-byte region [ffff8881071f4f00, ffff8881071f4f80)
    ==================================================================

Fixes: 2ff13894cfb8 ("Bluetooth: Perform HCI update for power on synchronously")
Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
---
Assisted-by: LLM

 net/bluetooth/smp.c | 36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index 0e442cc2a35da..552b6b3713c3a 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -3369,7 +3369,8 @@ int smp_force_bredr(struct hci_dev *hdev, bool enable)
 	return 0;
 }
 
-int smp_register(struct hci_dev *hdev)
+static int __smp_register(struct hci_dev *hdev)
+	__must_hold(&hdev->lock)
 {
 	struct l2cap_chan *chan;
 
@@ -3419,6 +3420,39 @@ int smp_register(struct hci_dev *hdev)
 	return 0;
 }
 
+struct smp_register_work {
+	struct work_struct work;
+	struct hci_dev *hdev;
+	int err;
+};
+
+static void smp_register_func(struct work_struct *work)
+{
+	struct smp_register_work *reg =
+		container_of(work, struct smp_register_work, work);
+	struct hci_dev *hdev = reg->hdev;
+
+	hci_dev_lock(hdev);
+	reg->err = __smp_register(hdev);
+	hci_dev_unlock(hdev);
+}
+
+int smp_register(struct hci_dev *hdev)
+{
+	struct smp_register_work reg = { .hdev = hdev };
+
+	/* HCI event handlers use the root channels under hdev->lock, and
+	 * SMP receive callbacks use them from hdev->workqueue. Replace the
+	 * channels from that workqueue while holding hdev->lock.
+	 */
+	INIT_WORK_ONSTACK(&reg.work, smp_register_func);
+	queue_work(hdev->workqueue, &reg.work);
+	flush_work(&reg.work);
+	destroy_work_on_stack(&reg.work);
+
+	return reg.err;
+}
+
 void smp_unregister(struct hci_dev *hdev)
 {
 	struct l2cap_chan *chan;