* [PATCH v2 1/2] Bluetooth: SMP: Serialize forced BR/EDR channel changes
2026-10-31 3:27 [PATCH v2 0/2] Bluetooth: SMP: Serialize root channel updates Cen Zhang
@ 2026-10-31 3:27 ` Cen Zhang
2026-10-31 3:27 ` [PATCH v2 2/2] Bluetooth: SMP: Serialize root channel replacement Cen Zhang
1 sibling, 0 replies; 3+ messages in thread
From: Cen Zhang @ 2026-10-31 3:27 UTC (permalink / raw)
To: marcel, luiz.dentz
Cc: linux-bluetooth, linux-kernel, baijiaju1990, jjzuming, zzzccc427
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);
^ permalink raw reply related [flat|nested] 3+ messages in thread* [PATCH v2 2/2] Bluetooth: SMP: Serialize root channel replacement
2026-10-31 3:27 [PATCH v2 0/2] Bluetooth: SMP: Serialize root channel updates Cen Zhang
2026-10-31 3:27 ` [PATCH v2 1/2] Bluetooth: SMP: Serialize forced BR/EDR channel changes Cen Zhang
@ 2026-10-31 3:27 ` Cen Zhang
1 sibling, 0 replies; 3+ messages in thread
From: Cen Zhang @ 2026-10-31 3:27 UTC (permalink / raw)
To: marcel, luiz.dentz
Cc: linux-bluetooth, linux-kernel, baijiaju1990, jjzuming, zzzccc427
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(®.work, smp_register_func);
+ queue_work(hdev->workqueue, ®.work);
+ flush_work(®.work);
+ destroy_work_on_stack(®.work);
+
+ return reg.err;
+}
+
void smp_unregister(struct hci_dev *hdev)
{
struct l2cap_chan *chan;
^ permalink raw reply related [flat|nested] 3+ messages in thread