Bluetooth: hci_conn: fix potential UAF in create_big_sync

PATCH Superseded David Carlier 3 participants 4 messages Apr 10 – Apr 11

Subsystems (3)

Stable branch Bluetooth drivers Bluetooth

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David Carlier

author

2026-04-10 17:34 UTC #0 lore raw

PATCH v2 1/1 Bluetooth: hci_conn: fix potential UAF in create_big_sync

Add hci_conn_valid() check in create_big_sync() to detect stale connections before proceeding with BIG creation. Fix create_big_complete() to handle the resulting -ECANCELED error and validate the connection under hci_dev_lock() before dereferencing, following the established pattern used by create_le_conn_complete() and create_pa_complete().

Without this, create_big_complete() would unconditionally dereference the stale conn pointer on error, causing a use-after-free via hci_connect_cfm() and hci_conn_del().

Fixes eca0ae4aea66 ("Bluetooth: Add initial implementation of BIS connections")

Cc [email protected]

Signed-off-by David Carlier <[email protected]>

---

v1 -> v2: fix create_big_complete() to handle -ECANCELED and
validate conn under hci_dev_lock(), matching the pattern in create_le_conn_complete() and create_pa_complete().
v1: https://lore.kernel.org/r/[email protected]

 net/bluetooth/hci_conn.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

net/bluetooth/hci_conn.c +14 -0

index 11d3ad8d2551..feebe933efc8 100644
@@ -2130,6 +2130,9 @@ static int create_big_sync(struct hci_dev *hdev, void *data)
 	u32 flags = 0;
 	int err;
 
+	if (!hci_conn_valid(hdev, conn))
+		return -ECANCELED;
+
 	if (qos->bcast.out.phys == BIT(1))
 		flags |= MGMT_ADV_FLAG_SEC_2M;

@@ -2204,11 +2207,22 @@ static void create_big_complete(struct hci_dev *hdev, void *data, int err)
 
 	bt_dev_dbg(hdev, "conn %p", conn);
 
+	if (err == -ECANCELED)
+		return;
+
+	hci_dev_lock(hdev);
+
+	if (!hci_conn_valid(hdev, conn))
+		goto done;
+
 	if (err) {
 		bt_dev_err(hdev, "Unable to create BIG: %d", err);
 		hci_connect_cfm(conn, err);
 		hci_conn_del(conn);
 	}
+
+done:
+	hci_dev_unlock(hdev);
 }
 
 struct hci_conn *hci_bind_bis(struct hci_dev *hdev, bdaddr_t *dst, __u8 sid,

Signature · 1 line

2.53.0

[email protected]

2026-04-10 18:32 UTC #1 lore raw

This is automated email and please do not reply to this email!

Dear submitter,

Thank you for submitting the patches to the linux bluetooth mailing list. This is a CI test results with your patch series:
PW Link:https://patchwork.kernel.org/project/bluetooth/list/?series=1079876

---Test result---

Test Summary:

CheckPatch                    PENDING   0.45 seconds
GitLint                       PENDING   0.29 seconds
SubjectPrefix                 PASS      0.12 seconds
BuildKernel                   PASS      26.84 seconds
CheckAllWarning               PASS      29.19 seconds
CheckSparse                   PASS      34.39 seconds
BuildKernel32                 PASS      26.53 seconds
TestRunnerSetup               PASS      578.39 seconds
TestRunner_l2cap-tester       PASS      28.77 seconds
TestRunner_iso-tester         PASS      46.74 seconds
TestRunner_bnep-tester        PASS      6.39 seconds
TestRunner_mgmt-tester        FAIL      114.92 seconds
TestRunner_rfcomm-tester      PASS      9.50 seconds
TestRunner_sco-tester         FAIL      14.83 seconds
TestRunner_ioctl-tester       PASS      10.53 seconds
TestRunner_mesh-tester        FAIL      12.51 seconds
TestRunner_smp-tester         PASS      8.75 seconds
TestRunner_userchan-tester    PASS      6.79 seconds
TestRunner_6lowpan-tester     FAIL      8.83 seconds
IncrementalBuild              PENDING   0.31 seconds

Details
##############################
Test: CheckPatch - PENDING
Desc: Run checkpatch.pl script
Output:

##############################
Test: GitLint - PENDING
Desc: Run gitlint
Output:

##############################
Test: TestRunner_mgmt-tester - FAIL
Desc: Run mgmt-tester with test-runner Output:
Total: 494, Passed: 489 (99.0%), Failed: 1, Not Run: 4

Failed Test Cases
Read Exp Feature - Success Failed 0.106 seconds
##############################
Test: TestRunner_sco-tester - FAIL
Desc: Run sco-tester with test-runner
Output:
WARNING: possible circular locking dependency detected
7.0.0-rc2-g3db70c75fd3b #1 Not tainted
------------------------------------------------------
kworker/u5:2/117 is trying to acquire lock:
ffff888001946240 (sk_lock-AF_BLUETOOTH-BTPROTO_SCO){+.+.}-{0:0}, at: sco_connect_cfm+0x358/0x8d0

but task is already holding lock:
ffff8880020cb220 (&conn->lock){+.+.}-{3:3}, at: sco_connect_cfm+0x22d/0x8d0

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&conn->lock){+.+.}-{3:3}:

       lock_acquire+0xf7/0x2c0
       _raw_spin_lock+0x2a/0x40
       sco_sock_connect+0x4d7/0x1280
       __sys_connect+0x1a3/0x260
       __x64_sys_connect+0x6e/0xb0
       do_syscall_64+0xa0/0x570
       entry_SYSCALL_64_after_hwframe+0x74/0x7c

-> #0 (sk_lock-AF_BLUETOOTH-BTPROTO_SCO){+.+.}-{0:0}:

       check_prev_add+0xe9/0xc70
       __lock_acquire+0x1457/0x1df0
       lock_acquire+0xf7/0x2c0
       lock_sock_nested+0x36/0xd0
       sco_connect_cfm+0x358/0x8d0
       hci_sync_conn_complete_evt+0x3d3/0x8e0
       hci_event_packet+0x74f/0xb10
       hci_rx_work+0x398/0xd00
       process_scheduled_works+0xb16/0x1ac0
       worker_thread+0x4ff/0xba0
       kthread+0x368/0x490
       ret_from_fork+0x498/0x7e0
       ret_from_fork_asm+0x19/0x30

other info that might help us debug this:

...

BUG: sleeping function called from invalid context at net/core/sock.c:3782

in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 117, name: kworker/u5:2
preempt_count: 1, expected: 0
RCU nest depth: 0, expected: 0
INFO: lockdep is turned off.

CPU: 0 UID: 0 PID: 117 Comm: kworker/u5:2 Not tainted 7.0.0-rc2-g3db70c75fd3b #1 PREEMPT(lazy) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-1ubuntu1.1 04/01/2014
Workqueue: hci0 hci_rx_work
Call Trace:
 <TASK>
 dump_stack_lvl+0x49/0x60
 __might_resched+0x2ea/0x500
 lock_sock_nested+0x47/0xd0
 ? sco_connect_cfm+0x358/0x8d0
 sco_connect_cfm+0x358/0x8d0
 ? hci_debugfs_create_conn+0x190/0x210
 ? __pfx_sco_connect_cfm+0x10/0x10
 hci_sync_conn_complete_evt+0x3d3/0x8e0
 hci_event_packet+0x74f/0xb10
 ? __pfx_hci_sync_conn_complete_evt+0x10/0x10
 ? __pfx_hci_event_packet+0x10/0x10
 ? mark_held_locks+0x49/0x80
 ? lockdep_hardirqs_on_prepare+0xd4/0x180
 ? _raw_spin_unlock_irqrestore+0x2c/0x50
 hci_rx_work+0x398/0xd00
 process_scheduled_works+0xb16/0x1ac0
 ? __pfx_process_scheduled_works+0x10/0x10
 ? lock_acquire+0xf7/0x2c0
 ? lock_is_held_type+0x9b/0x110
 ? __pfx_hci_rx_work+0x10/0x10
 worker_thread+0x4ff/0xba0
 ? _raw_spin_unlock_irqrestore+0x2c/0x50
 ? __pfx_worker_thread+0x10/0x10
 kthread+0x368/0x490
 ? _raw_spin_unlock_irq+0x23/0x40
 ? __pfx_kthread+0x10/0x10
 ret_from_fork+0x498/0x7e0
 ? __pfx_ret_from_fork+0x10/0x10
 ? __switch_to+0x9e4/0xe50
 ? __switch_to_asm+0x32/0x60

...
Total: 30, Passed: 30 (100.0%), Failed: 0, Not Run: 0
##############################
Test: TestRunner_mesh-tester - FAIL
Desc: Run mesh-tester with test-runner Output:
Total: 10, Passed: 8 (80.0%), Failed: 2, Not Run: 0

Failed Test Cases

Mesh - Send cancel - 1                               Timed out    2.738 seconds
Mesh - Send cancel - 2                               Timed out    1.998 seconds

##############################
Test: TestRunner_6lowpan-tester - FAIL
Desc: Run 6lowpan-tester with test-runner
Output:
WARNING: possible circular locking dependency detected 7.0.0-rc2-g3db70c75fd3b #1 Not tainted
------------------------------------------------------
kworker/0:1/11 is trying to acquire lock:
ffff8880026e4940 ((wq_completion)hci0#2){+.+.}-{0:0}, at: touch_wq_lockdep_map+0x75/0x180

but task is already holding lock:
ffffffff9a64d720 (rtnl_mutex){+.+.}-{4:4}, at: lowpan_unregister_netdev+0xd/0x30

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #4 (rtnl_mutex){+.+.}-{4:4}:

       lock_acquire+0xf7/0x2c0
       __mutex_lock+0x16b/0x1fc0
       lowpan_register_netdev+0x11/0x30
       chan_ready_cb+0x836/0xd00
       l2cap_recv_frame+0x6a06/0x8920
       l2cap_recv_acldata+0x790/0xdf0
       hci_rx_work+0x500/0xd00
       process_scheduled_works+0xb16/0x1ac0
       worker_thread+0x4ff/0xba0
       kthread+0x368/0x490
       ret_from_fork+0x498/0x7e0
       ret_from_fork_asm+0x19/0x30

-> #3 (&chan->lock#3/1){+.+.}-{4:4}:

       lock_acquire+0xf7/0x2c0
       __mutex_lock+0x16b/0x1fc0
       l2cap_chan_connect+0x74e/0x1980
       lowpan_control_write+0x523/0x660
       full_proxy_write+0x10b/0x190
       vfs_write+0x1c0/0xf60
       ksys_write+0xf1/0x1d0
       do_syscall_64+0xa0/0x570
       entry_SYSCALL_64_after_hwframe+0x74/0x7c

-> #2 (&conn->lock){+.+.}-{4:4}:
...
Total: 8, Passed: 8 (100.0%), Failed: 0, Not Run: 0
##############################
Test: IncrementalBuild - PENDING
Desc: Incremental build with the patches in the series Output:

https://github.com/bluez/bluetooth-next/pull/64

---
Regards,
Linux Bluetooth

Paul Menzel

2026-04-10 20:25 UTC #2 lore raw

In reply to David Carlier

Dear David,

Thank you for the patch.

Am 10.04.26 um 19:34 schrieb David Carlier:

Quoted 6 lines

Add hci_conn_valid() check in create_big_sync() to detect stale connections before proceeding with BIG creation. Fix create_big_complete() to handle the resulting -ECANCELED error and validate the connection under hci_dev_lock() before dereferencing, following the established pattern used by create_le_conn_complete() and create_pa_complete().

(Using 75 characters per line would save a line.)

Quoted 21 lines

Without this, create_big_complete() would unconditionally dereference the stale conn pointer on error, causing a use-after-free via hci_connect_cfm() and hci_conn_del().
Fixes eca0ae4aea66 ("Bluetooth: Add initial implementation of BIS connections")
Cc [email protected]
Signed-off-by David Carlier <[email protected]>
---
v1 -> v2: fix create_big_complete() to handle -ECANCELED and
validate conn under hci_dev_lock(), matching the pattern in create_le_conn_complete() and create_pa_complete().
v1: https://lore.kernel.org/r/[email protected]
  net/bluetooth/hci_conn.c | 14 ++++++++++++++
  1 file changed, 14 insertions(+)
net/bluetooth/hci_conn.c +0 -0
index 11d3ad8d2551..feebe933efc8 100644

net/bluetooth/hci_conn.c static int create_big_sync(struct hci_dev *hdev, void *data) · line 2135

Quoted 6 lines

net/bluetooth/hci_conn.c +3 -0

@@ -2130,6 +2130,9 @@ static int create_big_sync(struct hci_dev *hdev, void *data)
  	u32 flags = 0;
  	int err;
 
+	if (!hci_conn_valid(hdev, conn))
+		return -ECANCELED;
+

I wonder if a debug message about the stale connection would be useful.

gemini/gemini-3.1-pro-preview comments [1]:

Quoted 35 lines

Could this introduce a time-of-check to time-of-use race condition? Because create_big_sync() executes asynchronously in the cmd_sync_work workqueue without holding hci_dev_lock(), hci_conn_valid() only protects the lookup for the duration of its internal rcu_read_lock(). If a concurrent thread acquires hci_dev_lock() and calls hci_conn_del() immediately after hci_conn_valid() returns true:
cpu 1
create_big_sync()
if (!hci_conn_valid(hdev, conn))
return -ECANCELED;
cpu 2
hci_dev_lock(hdev);
hci_conn_del(conn);
hci_dev_unlock(hdev);
cpu 1
    if (qos->bcast.out.phys == BIT(1))
Will this lead to a use-after-free on the conn pointer since qos resolves to &conn->iso_qos?
Additionally, since conn is passed to the workqueue without holding a reference via hci_conn_get(), could this be susceptible to a pointer reuse problem?
If the original connection is freed and the memory is reallocated for a new, unrelated connection before the work runs, hci_conn_valid() might incorrectly return true. This could cause the new connection to be wrongly operated on or deleted later in create_big_complete().
Does the caller queueing the work need to take a proper reference with hci_conn_get() and release it in the completion callback instead? [ ... ]
  	if (qos->bcast.out.phys == BIT(1))
  		flags |= MGMT_ADV_FLAG_SEC_2M;

net/bluetooth/hci_conn.c static void create_big_complete(struct hci_dev *hdev, void *data, int err) · line 2211

Quoted 5 lines

net/bluetooth/hci_conn.c +2 -0

@@ -2204,11 +2207,22 @@ static void create_big_complete(struct hci_dev *hdev, void *data, int err)
 
  	bt_dev_dbg(hdev, "conn %p", conn);
 
+	if (err == -ECANCELED)
+		return;

Should the error message still be printed in this case?

    bt_dev_err(hdev, "Unable to create BIG: ECANCELED");

Quoted 7 lines

net/bluetooth/hci_conn.c +6 -0

+
+	hci_dev_lock(hdev);
+
+	if (!hci_conn_valid(hdev, conn))
+		goto done;
+
  	if (err) {

net/bluetooth/hci_conn.c static void create_big_complete(struct hci_dev *hdev, void *data, int err) · line 2228

Quoted 10 lines

net/bluetooth/hci_conn.c +3 -0

  		bt_dev_err(hdev, "Unable to create BIG: %d", err);
  		hci_connect_cfm(conn, err);
  		hci_conn_del(conn);
  	}
+
+done:
+	hci_dev_unlock(hdev);
  }
 
  struct hci_conn *hci_bind_bis(struct hci_dev *hdev, bdaddr_t *dst, __u8 sid,

Kind regards,

Paul

[1]: https://sashiko.dev/#/patchset/20260410173451.4797-1-devnexen%40gmail.com

David CARLIER

author

2026-04-11 04:16 UTC #3 lore raw

Hi Paul,

Thanks a lot for taking the time to look at this.

Quoted 1 line

(Using 75 characters per line would save a line.)

Good catch, I'll rewrap it in v3.

Quoted 1 line

I wonder if a debug message about the stale connection would be

useful.

Yes, that makes sense — I'll add a bt_dev_dbg() right before the -ECANCELED return so it's visible when debugging.

Quoted 2 lines

gemini/gemini-3.1-pro-preview comments [1]:
Quoted 1 line
Could this introduce a time-of-check to time-of-use race

condition?

Quoted 1 line

[ ... ]

I had the same reflex when I first looked at it, but I think the tool is reading the check in isolation. The hci_conn_valid() at the top
of
a *_sync callback is really just a "did this connection get torn down before the work ran?" guard — it's the same idiom already used by hci_le_create_conn_sync(), hci_le_pa_create_sync() and hci_le_big_create_sync() in hci_sync.c. It was never meant to fully serialize against a concurrent hci_conn_del().

The piece that actually closes the UAF in v2 is in create_big_complete(): it now takes hci_dev_lock() and re-validates conn before dereferencing it, which mirrors what
create_pa_complete()
does. That's the part doing the real work here.

If there's a genuine strict-TOCTOU window between the valid check and the &conn->iso_qos access inside create_big_sync(), it would equally affect every other *_sync user of the same idiom, so I'd rather not try to rework that in this fix — happy to revisit it separately if you think it's worth digging into.

Quoted 4 lines

Quoted 2 lines
+ if (err == -ECANCELED)
+ return;
Should the error message still be printed in this case?

I went back and forth on that one. In the end I kept it silent to stay consistent with create_pa_complete() in hci_sync.c, which also just returns on -ECANCELED without logging. Happy to add a print if you'd rather have one, though.

I'll send a v3 with the rewrap and the debug message in a timely manner.

Cheers !

Quoted 119 lines · Paul Menzel

Dear David,
Thank you for the patch.
Am 10.04.26 um 19:34 schrieb David Carlier:
Quoted 6 lines
Add hci_conn_valid() check in create_big_sync() to detect stale connections before proceeding with BIG creation. Fix create_big_complete() to handle the resulting -ECANCELED error and validate the connection under hci_dev_lock() before dereferencing, following the established pattern used by create_le_conn_complete() and create_pa_complete().
(Using 75 characters per line would save a line.)
Quoted 21 lines
Without this, create_big_complete() would unconditionally dereference the stale conn pointer on error, causing a use-after-free via hci_connect_cfm() and hci_conn_del().
Fixes eca0ae4aea66 ("Bluetooth: Add initial implementation of BIS connections")
Cc [email protected]
Signed-off-by David Carlier <[email protected]>
---
v1 -> v2: fix create_big_complete() to handle -ECANCELED and
validate conn under hci_dev_lock(), matching the pattern in create_le_conn_complete() and create_pa_complete().
v1: https://lore.kernel.org/r/[email protected]
  net/bluetooth/hci_conn.c | 14 ++++++++++++++
  1 file changed, 14 insertions(+)
net/bluetooth/hci_conn.c +0 -0
index 11d3ad8d2551..feebe933efc8 100644
net/bluetooth/hci_conn.c static int create_big_sync(struct hci_dev *hdev, void *data) · line 2135
Quoted 6 lines
net/bluetooth/hci_conn.c +3 -0
@@ -2130,6 +2130,9 @@ static int create_big_sync(struct hci_dev *hdev, void *data)
      u32 flags = 0;
      int err;
 
+     if (!hci_conn_valid(hdev, conn))
+             return -ECANCELED;
+
I wonder if a debug message about the stale connection would be useful.
gemini/gemini-3.1-pro-preview comments [1]:
Quoted 35 lines
Could this introduce a time-of-check to time-of-use race condition? Because create_big_sync() executes asynchronously in the cmd_sync_work workqueue without holding hci_dev_lock(), hci_conn_valid() only protects the lookup for the duration of its internal rcu_read_lock(). If a concurrent thread acquires hci_dev_lock() and calls hci_conn_del() immediately after hci_conn_valid() returns true:
cpu 1
create_big_sync()
if (!hci_conn_valid(hdev, conn))
return -ECANCELED;
cpu 2
hci_dev_lock(hdev);
hci_conn_del(conn);
hci_dev_unlock(hdev);
cpu 1
    if (qos->bcast.out.phys == BIT(1))
Will this lead to a use-after-free on the conn pointer since qos resolves to &conn->iso_qos?
Additionally, since conn is passed to the workqueue without holding a reference via hci_conn_get(), could this be susceptible to a pointer reuse problem?
If the original connection is freed and the memory is reallocated for a new, unrelated connection before the work runs, hci_conn_valid() might incorrectly return true. This could cause the new connection to be wrongly operated on or deleted later in create_big_complete().
Does the caller queueing the work need to take a proper reference with hci_conn_get() and release it in the completion callback instead? [ ... ]
      if (qos->bcast.out.phys == BIT(1))
              flags |= MGMT_ADV_FLAG_SEC_2M;
net/bluetooth/hci_conn.c static void create_big_complete(struct hci_dev *hdev, void *data, int err) · line 2211
Quoted 5 lines
net/bluetooth/hci_conn.c +2 -0
@@ -2204,11 +2207,22 @@ static void create_big_complete(struct hci_dev *hdev, void *data, int err)
 
      bt_dev_dbg(hdev, "conn %p", conn);
 
+     if (err == -ECANCELED)
+             return;
Should the error message still be printed in this case?
     bt_dev_err(hdev, "Unable to create BIG: ECANCELED");
Quoted 7 lines
net/bluetooth/hci_conn.c +6 -0
+
+     hci_dev_lock(hdev);
+
+     if (!hci_conn_valid(hdev, conn))
+             goto done;
+
      if (err) {
net/bluetooth/hci_conn.c static void create_big_complete(struct hci_dev *hdev, void *data, int err) · line 2228
Quoted 10 lines
net/bluetooth/hci_conn.c +3 -0
              bt_dev_err(hdev, "Unable to create BIG: %d", err);
              hci_connect_cfm(conn, err);
              hci_conn_del(conn);
      }
+
+done:
+     hci_dev_unlock(hdev);
  }
 
  struct hci_conn *hci_bind_bis(struct hci_dev *hdev, bdaddr_t *dst, __u8 sid,
Kind regards,
Paul
[1]:
https://sashiko.dev/#/patchset/20260410173451.4797-1-devnexen%40gmail.com