[PATCH v2 net-next] Bluetooth: hci_conn: fix potential UAF in create_big_sync

[PATCH v2 net-next] Bluetooth: hci_conn: fix potential UAF in create_big_sync

[David Carlier]

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: stable@vger.kernel.org
Signed-off-by: David Carlier <devnexen@gmail.com>
---

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/20260408155638.95927-1-devnexen@gmail.com
 net/bluetooth/hci_conn.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index 11d3ad8d2551..feebe933efc8 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -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,
-- 
2.53.0

RE: [v2,net-next] Bluetooth: hci_conn: fix potential UAF in create_big_sync

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 6870 bytes --]

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

Re: [PATCH v2 net-next] Bluetooth: hci_conn: fix potential UAF in create_big_sync

[Paul Menzel]

Dear David,


Thank you for the patch.

Am 10.04.26 um 19:34 schrieb David Carlier:
> 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.)

> 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: stable@vger.kernel.org
> Signed-off-by: David Carlier <devnexen@gmail.com>
> ---
> 
> 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/20260408155638.95927-1-devnexen@gmail.com
>   net/bluetooth/hci_conn.c | 14 ++++++++++++++
>   1 file changed, 14 insertions(+)
> 
> diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
> index 11d3ad8d2551..feebe933efc8 100644
> --- a/net/bluetooth/hci_conn.c
> +++ b/net/bluetooth/hci_conn.c
> @@ -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]:

> 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;
>   
> @@ -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");

> +
> +	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,


Kind regards,

Paul


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

Re: [PATCH v2 net-next] Bluetooth: hci_conn: fix potential UAF in create_big_sync

[David CARLIER]

Hi Paul,

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

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

  Good catch, I'll rewrap it in v3.

  > 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.

  > gemini/gemini-3.1-pro-preview comments [1]:
  > > Could this introduce a time-of-check to time-of-use race
condition?
  > [ ... ]

  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.

  > > + 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 !

On Fri, 10 Apr 2026 at 21:25, Paul Menzel <pmenzel@molgen.mpg.de> wrote:
>
> Dear David,
>
>
> Thank you for the patch.
>
> Am 10.04.26 um 19:34 schrieb David Carlier:
> > 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.)
>
> > 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: stable@vger.kernel.org
> > Signed-off-by: David Carlier <devnexen@gmail.com>
> > ---
> >
> > 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/20260408155638.95927-1-devnexen@gmail.com
> >   net/bluetooth/hci_conn.c | 14 ++++++++++++++
> >   1 file changed, 14 insertions(+)
> >
> > diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
> > index 11d3ad8d2551..feebe933efc8 100644
> > --- a/net/bluetooth/hci_conn.c
> > +++ b/net/bluetooth/hci_conn.c
> > @@ -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]:
>
> > 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;
> >
> > @@ -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");
>
> > +
> > +     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,
>
>
> Kind regards,
>
> Paul
>
>
> [1]:
> https://sashiko.dev/#/patchset/20260410173451.4797-1-devnexen%40gmail.com