[PATCH v2] Bluetooth: hci_sync: fix UAF in hci_le_create_cis_sync

[Doruk Tan Ozturk <doruk@0sec.ai>]

hci_le_create_cis_sync() dereferences conn->conn_timeout after releasing
both rcu_read_lock() and hci_dev_lock(hdev).  The conn pointer was
obtained from an RCU-protected iteration over hdev->conn_hash.list and
is not valid once these locks are dropped.  A concurrent disconnect can
free the hci_conn between the unlock and the dereference, causing a
use-after-free read.

The cancellation mechanism in hci_conn_del() cannot prevent this because
hci_le_create_cis_pending() queues hci_create_cis_sync with data=NULL:

    hci_cmd_sync_queue(hdev, hci_create_cis_sync, NULL, NULL);

While hci_conn_del() dequeues with data=conn:

    hci_cmd_sync_dequeue(hdev, NULL, conn, NULL);

Since NULL != conn, the lookup in _hci_cmd_sync_lookup_entry() never
matches, and the pending work item is not cancelled.

Fix this by saving conn->conn_timeout into a local variable while the
locks are still held, so the stale conn pointer is never dereferenced
after unlock.

This is the same class of bug as the one fixed by commit
035c25007c9e ("Bluetooth: hci_sync: Fix UAF in
le_read_features_complete") which addressed the identical pattern in a
different function.

Found by 0sec (https://0sec.ai) using automated source analysis.

Fixes: c09b80be6ffc ("Bluetooth: hci_conn: Fix not waiting for HCI_EVT_LE_CIS_ESTABLISHED")
Cc: stable@vger.kernel.org
Reported-by: Doruk Tan Ozturk <doruk@0sec.ai>
Closes: https://lore.kernel.org/linux-bluetooth/20260525162438.96881-1-doruk@0sec.ai/
Signed-off-by: Doruk Tan Ozturk <doruk@0sec.ai>
---
v2:
  - fix commit reference title ("Fix UAF in" not "Fix UAF on")
  - fix Fixes: tag title to match actual commit
  - add Closes: tag per checkpatch

Link: https://lore.kernel.org/linux-bluetooth/20260525162438.96881-1-doruk@0sec.ai/

 net/bluetooth/hci_sync.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
index XXXXXXX..XXXXXXX 100644
--- a/net/bluetooth/hci_sync.c
+++ b/net/bluetooth/hci_sync.c
@@ -6700,6 +6700,7 @@ int hci_le_create_cis_sync(struct hci_dev *hdev)
 	DEFINE_FLEX(struct hci_cp_le_create_cis, cmd, cis, num_cis, 0x1f);
 	size_t aux_num_cis = 0;
 	struct hci_conn *conn;
+	u16 timeout = 0;
 	u8 cig = BT_ISO_QOS_CIG_UNSET;

 	/* The spec allows only one pending LE Create CIS command at a time. If
@@ -6773,6 +6774,7 @@ int hci_le_create_cis_sync(struct hci_dev *hdev)
 		set_bit(HCI_CONN_CREATE_CIS, &conn->flags);
 		cis->acl_handle = cpu_to_le16(conn->parent->handle);
 		cis->cis_handle = cpu_to_le16(conn->handle);
+		timeout = conn->conn_timeout;
 		aux_num_cis++;

 		if (aux_num_cis >= cmd->num_cis)
@@ -6791,7 +6793,7 @@ int hci_le_create_cis_sync(struct hci_dev *hdev)
 	return __hci_cmd_sync_status_sk(hdev, HCI_OP_LE_CREATE_CIS,
 					struct_size(cmd, cis, cmd->num_cis),
 					cmd, HCI_EVT_LE_CIS_ESTABLISHED,
-					conn->conn_timeout, NULL);
+					timeout, NULL);
 }

 int hci_le_remove_cig_sync(struct hci_dev *hdev, u8 handle)
--
2.45.0