[PATCH] Bluetooth: fix use-after-free in hci_conn_drop

[PATCH] Bluetooth: fix use-after-free in hci_conn_drop

[Masahiro Kawada]

Fix a use-after-free in hci_conn_drop triggered via hci_cmd_sync_work.

In hci_conn_del(), hci_cmd_sync_dequeue() is called after
hci_conn_cleanup() which may have already freed the conn pointer.
Fix by moving the dequeue before cleanup.

Additionally, le_read_features_complete() calls hci_conn_drop(conn)
without checking whether conn is still valid. When
hci_le_read_remote_features_sync() blocks waiting for an HCI event,
another thread can free conn through hci_conn_del(). Fix by adding
a hci_conn_valid() check before calling hci_conn_drop().

Fixes: 881559af5f5c ("Bluetooth: hci_sync: Attempt to dequeue connection attempt")
Fixes: a106e50be74b ("Bluetooth: HCI: Add support for LL Extended Feature Set")
Reported-by: syzbot+3609b9b48e68e1fe47fd@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3609b9b48e68e1fe47fd
Tested-by: syzbot+3609b9b48e68e1fe47fd@syzkaller.appspotmail.com
Signed-off-by: Masahiro Kawada <youjingxiaogao2@gmail.com>
---
 net/bluetooth/hci_conn.c | 6 +++---
 net/bluetooth/hci_sync.c | 3 +++
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index 0795818963a..aa3607327ad 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -1232,15 +1232,15 @@ void hci_conn_del(struct hci_conn *conn)
 	skb_queue_purge(&conn->data_q);
 	skb_queue_purge(&conn->tx_q.queue);
 
+	/* Dequeue callbacks using connection pointer as data */
+	hci_cmd_sync_dequeue(hdev, NULL, conn, NULL);
+
 	/* Remove the connection from the list and cleanup its remaining
 	 * state. This is a separate function since for some cases like
 	 * BT_CONNECT_SCAN we *only* want the cleanup part without the
 	 * rest of hci_conn_del.
 	 */
 	hci_conn_cleanup(conn);
-
-	/* Dequeue callbacks using connection pointer as data */
-	hci_cmd_sync_dequeue(hdev, NULL, conn, NULL);
 }
 
 struct hci_dev *hci_get_route(bdaddr_t *dst, bdaddr_t *src, uint8_t src_type)
diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
index f04a90bce4a..f31086c187f 100644
--- a/net/bluetooth/hci_sync.c
+++ b/net/bluetooth/hci_sync.c
@@ -7371,6 +7371,9 @@ static void le_read_features_complete(struct hci_dev *hdev, void *data, int err)
 	if (err == -ECANCELED)
 		return;
 
+	if (!hci_conn_valid(hdev, conn))
+		return;
+
 	hci_conn_drop(conn);
 }
 
-- 
2.43.0

Re: [PATCH] Bluetooth: fix use-after-free in hci_conn_drop

[Hillf Danton]

On Mon,  9 Feb 2026 19:02:11 +0900 Masahiro Kawada wrote:
> Fix a use-after-free in hci_conn_drop triggered via hci_cmd_sync_work.
> 
> In hci_conn_del(), hci_cmd_sync_dequeue() is called after
> hci_conn_cleanup() which may have already freed the conn pointer.
> Fix by moving the dequeue before cleanup.
> 
> Additionally, le_read_features_complete() calls hci_conn_drop(conn)
> without checking whether conn is still valid. When
> hci_le_read_remote_features_sync() blocks waiting for an HCI event,
> another thread can free conn through hci_conn_del(). Fix by adding
> a hci_conn_valid() check before calling hci_conn_drop().
> 
> Fixes: 881559af5f5c ("Bluetooth: hci_sync: Attempt to dequeue connection attempt")
> Fixes: a106e50be74b ("Bluetooth: HCI: Add support for LL Extended Feature Set")
> Reported-by: syzbot+3609b9b48e68e1fe47fd@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=3609b9b48e68e1fe47fd
> Tested-by: syzbot+3609b9b48e68e1fe47fd@syzkaller.appspotmail.com
> Signed-off-by: Masahiro Kawada <youjingxiaogao2@gmail.com>
> ---
>  net/bluetooth/hci_conn.c | 6 +++---
>  net/bluetooth/hci_sync.c | 3 +++
>  2 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
> index 0795818963a..aa3607327ad 100644
> --- a/net/bluetooth/hci_conn.c
> +++ b/net/bluetooth/hci_conn.c
> @@ -1232,15 +1232,15 @@ void hci_conn_del(struct hci_conn *conn)
>  	skb_queue_purge(&conn->data_q);
>  	skb_queue_purge(&conn->tx_q.queue);
>  
> +	/* Dequeue callbacks using connection pointer as data */
> +	hci_cmd_sync_dequeue(hdev, NULL, conn, NULL);
> +
>  	/* Remove the connection from the list and cleanup its remaining
>  	 * state. This is a separate function since for some cases like
>  	 * BT_CONNECT_SCAN we *only* want the cleanup part without the
>  	 * rest of hci_conn_del.
>  	 */
>  	hci_conn_cleanup(conn);
> -
> -	/* Dequeue callbacks using connection pointer as data */
> -	hci_cmd_sync_dequeue(hdev, NULL, conn, NULL);
>  }
>  
>  struct hci_dev *hci_get_route(bdaddr_t *dst, bdaddr_t *src, uint8_t src_type)
> diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
> index f04a90bce4a..f31086c187f 100644
> --- a/net/bluetooth/hci_sync.c
> +++ b/net/bluetooth/hci_sync.c
> @@ -7371,6 +7371,9 @@ static void le_read_features_complete(struct hci_dev *hdev, void *data, int err)
>  	if (err == -ECANCELED)
>  		return;
>  
> +	if (!hci_conn_valid(hdev, conn))
> +		return;
> +
>  	hci_conn_drop(conn);
>  }
>  
> -- 
> 2.43.0
>
The uaf [1] is due to the following race,

	cpu1				cpu2
	hci_cmd_sync_work()		hci_rx_work()
	mutex_lock(&hdev->cmd_sync_work_lock);
	entry = list_first_entry_or_null(&hdev->cmd_sync_work_list,
					 struct hci_cmd_sync_work_entry,
					 list);
	if (entry)
		list_del(&entry->list);
	mutex_unlock(&hdev->cmd_sync_work_lock);

					hci_conn_del()
					hci_conn_hash_del(hdev, conn);
					hci_conn_cleanup(conn)	// free conn
					hci_cmd_sync_dequeue()
					mutex_lock(&hdev->cmd_sync_work_lock);
					while ((entry = _hci_cmd_sync_lookup_entry(hdev, func, data,
						   destroy))) {
						_hci_cmd_sync_cancel_entry(hdev, entry, -ECANCELED);
						ret = true;
					}
					mutex_unlock(&hdev->cmd_sync_work_lock);

	hci_req_sync_lock(hdev);
	err = entry->func(hdev, entry->data);
	if (entry->destroy)
		entry->destroy(hdev, entry->data, err);
		hci_conn_drop(conn)	// uaf
	hci_req_sync_unlock(hdev);

but the race still exists after this patch.

	cpu1				cpu2
	hci_conn_valid(hdev, conn)
					hci_conn_hash_del(hdev, conn);
					hci_cmd_sync_dequeue()
					hci_conn_cleanup(conn)	// free conn
	hci_conn_drop(conn); // uaf

[1] Subject: [syzbot] [bluetooth?] KASAN: slab-use-after-free Write in hci_conn_drop (3)
https://lore.kernel.org/lkml/69301edd.a70a0220.2ea503.00cf.GAE@google.com/

Re: [PATCH] Bluetooth: fix use-after-free in hci_conn_drop

[kawada]

> but the race still exists after this patch.

I agree that the TOCTOU issue remains. I looked into all the functions
that can be called as entry->destroy in hci_cmd_sync_work where the
second argument (data) is used as hci_conn*. I found five such
functions across two files:

In hci_sync.c:
  - create_le_conn_complete
  - create_pa_complete
  - create_big_complete
  - le_read_features_complete

In hci_conn.c:
  - create_big_complete (separate static function)

Of these, create_le_conn_complete and create_pa_complete already use
hci_dev_lock, which effectively prevents this TOCTOU issue.

The remaining three are vulnerable:
  - create_big_complete in hci_sync.c calls hci_conn_valid without
    holding hci_dev_lock (TOCTOU)
  - le_read_features_complete calls hci_conn_drop with no validity
    check at all
  - create_big_complete in hci_conn.c calls hci_connect_cfm and
    hci_conn_del with no validity check at all

Given this, I believe the following set of patches would be
appropriate:

1. Reorder hci_cmd_sync_dequeue before hci_conn_cleanup in
   hci_conn_del
2. Wrap all three vulnerable callbacks with hci_dev_lock and
   hci_conn_valid, following the same pattern used by
   create_le_conn_complete and create_pa_complete

If this approach sounds reasonable, I will prepare updated patches.


2026年2月9日(月) 22:25 Hillf Danton <hdanton@sina.com>:
>
> On Mon,  9 Feb 2026 19:02:11 +0900 Masahiro Kawada wrote:
> > Fix a use-after-free in hci_conn_drop triggered via hci_cmd_sync_work.
> >
> > In hci_conn_del(), hci_cmd_sync_dequeue() is called after
> > hci_conn_cleanup() which may have already freed the conn pointer.
> > Fix by moving the dequeue before cleanup.
> >
> > Additionally, le_read_features_complete() calls hci_conn_drop(conn)
> > without checking whether conn is still valid. When
> > hci_le_read_remote_features_sync() blocks waiting for an HCI event,
> > another thread can free conn through hci_conn_del(). Fix by adding
> > a hci_conn_valid() check before calling hci_conn_drop().
> >
> > Fixes: 881559af5f5c ("Bluetooth: hci_sync: Attempt to dequeue connection attempt")
> > Fixes: a106e50be74b ("Bluetooth: HCI: Add support for LL Extended Feature Set")
> > Reported-by: syzbot+3609b9b48e68e1fe47fd@syzkaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=3609b9b48e68e1fe47fd
> > Tested-by: syzbot+3609b9b48e68e1fe47fd@syzkaller.appspotmail.com
> > Signed-off-by: Masahiro Kawada <youjingxiaogao2@gmail.com>
> > ---
> >  net/bluetooth/hci_conn.c | 6 +++---
> >  net/bluetooth/hci_sync.c | 3 +++
> >  2 files changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
> > index 0795818963a..aa3607327ad 100644
> > --- a/net/bluetooth/hci_conn.c
> > +++ b/net/bluetooth/hci_conn.c
> > @@ -1232,15 +1232,15 @@ void hci_conn_del(struct hci_conn *conn)
> >       skb_queue_purge(&conn->data_q);
> >       skb_queue_purge(&conn->tx_q.queue);
> >
> > +     /* Dequeue callbacks using connection pointer as data */
> > +     hci_cmd_sync_dequeue(hdev, NULL, conn, NULL);
> > +
> >       /* Remove the connection from the list and cleanup its remaining
> >        * state. This is a separate function since for some cases like
> >        * BT_CONNECT_SCAN we *only* want the cleanup part without the
> >        * rest of hci_conn_del.
> >        */
> >       hci_conn_cleanup(conn);
> > -
> > -     /* Dequeue callbacks using connection pointer as data */
> > -     hci_cmd_sync_dequeue(hdev, NULL, conn, NULL);
> >  }
> >
> >  struct hci_dev *hci_get_route(bdaddr_t *dst, bdaddr_t *src, uint8_t src_type)
> > diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
> > index f04a90bce4a..f31086c187f 100644
> > --- a/net/bluetooth/hci_sync.c
> > +++ b/net/bluetooth/hci_sync.c
> > @@ -7371,6 +7371,9 @@ static void le_read_features_complete(struct hci_dev *hdev, void *data, int err)
> >       if (err == -ECANCELED)
> >               return;
> >
> > +     if (!hci_conn_valid(hdev, conn))
> > +             return;
> > +
> >       hci_conn_drop(conn);
> >  }
> >
> > --
> > 2.43.0
> >
> The uaf [1] is due to the following race,
>
>         cpu1                            cpu2
>         hci_cmd_sync_work()             hci_rx_work()
>         mutex_lock(&hdev->cmd_sync_work_lock);
>         entry = list_first_entry_or_null(&hdev->cmd_sync_work_list,
>                                          struct hci_cmd_sync_work_entry,
>                                          list);
>         if (entry)
>                 list_del(&entry->list);
>         mutex_unlock(&hdev->cmd_sync_work_lock);
>
>                                         hci_conn_del()
>                                         hci_conn_hash_del(hdev, conn);
>                                         hci_conn_cleanup(conn)  // free conn
>                                         hci_cmd_sync_dequeue()
>                                         mutex_lock(&hdev->cmd_sync_work_lock);
>                                         while ((entry = _hci_cmd_sync_lookup_entry(hdev, func, data,
>                                                    destroy))) {
>                                                 _hci_cmd_sync_cancel_entry(hdev, entry, -ECANCELED);
>                                                 ret = true;
>                                         }
>                                         mutex_unlock(&hdev->cmd_sync_work_lock);
>
>         hci_req_sync_lock(hdev);
>         err = entry->func(hdev, entry->data);
>         if (entry->destroy)
>                 entry->destroy(hdev, entry->data, err);
>                 hci_conn_drop(conn)     // uaf
>         hci_req_sync_unlock(hdev);
>
> but the race still exists after this patch.
>
>         cpu1                            cpu2
>         hci_conn_valid(hdev, conn)
>                                         hci_conn_hash_del(hdev, conn);
>                                         hci_cmd_sync_dequeue()
>                                         hci_conn_cleanup(conn)  // free conn
>         hci_conn_drop(conn); // uaf
>
> [1] Subject: [syzbot] [bluetooth?] KASAN: slab-use-after-free Write in hci_conn_drop (3)
> https://lore.kernel.org/lkml/69301edd.a70a0220.2ea503.00cf.GAE@google.com/

Re: [PATCH] Bluetooth: fix use-after-free in hci_conn_drop

[Hillf Danton]

[ hm... top reply looks no good ]

On Tue, 10 Feb 2026 15:08:12 +0900 Masahiro Kawada wrote:
> > but the race still exists after this patch.
> 
> I agree that the TOCTOU issue remains. I looked into all the functions
> that can be called as entry->destroy in hci_cmd_sync_work where the
> second argument (data) is used as hci_conn*. I found five such
> functions across two files:
> 
> In hci_sync.c:
>   - create_le_conn_complete
>   - create_pa_complete
>   - create_big_complete
>   - le_read_features_complete
> 
> In hci_conn.c:
>   - create_big_complete (separate static function)
> 
> Of these, create_le_conn_complete and create_pa_complete already use
> hci_dev_lock, which effectively prevents this TOCTOU issue.
> 
> The remaining three are vulnerable:
>   - create_big_complete in hci_sync.c calls hci_conn_valid without
>     holding hci_dev_lock (TOCTOU)
>   - le_read_features_complete calls hci_conn_drop with no validity
>     check at all
>   - create_big_complete in hci_conn.c calls hci_connect_cfm and
>     hci_conn_del with no validity check at all
> 
> Given this, I believe the following set of patches would be
> appropriate:
> 
> 1. Reorder hci_cmd_sync_dequeue before hci_conn_cleanup in
>    hci_conn_del
> 2. Wrap all three vulnerable callbacks with hci_dev_lock and
>    hci_conn_valid, following the same pattern used by
>    create_le_conn_complete and create_pa_complete
> 
> If this approach sounds reasonable, I will prepare updated patches.
>
Better not before spotting the reason why conn->refcnt failed to make the
entry->destroy callback safe, given the complexity of the race.

Re: [PATCH] Bluetooth: fix use-after-free in hci_conn_drop

[kawada]

Apologies for the top-posting.

> Better not before spotting the reason why conn->refcnt
> failed to make the entry->destroy callback safe.

hci_conn_hold() increments conn->refcnt, but the actual
freeing of conn is done by put_device() called from
hci_conn_del(). hci_conn_del() does not check conn->refcnt
at all, so the hold/drop refcount cannot prevent the UAF
in entry->destroy callbacks.