[PATCH] Bluetooth: ISO: avoid NULL deref of conn in iso_conn_big_sync()

[Muhammad Bilal <meatuni001@gmail.com>]

iso_conn_big_sync() drops the socket lock to call hci_get_route() and
then re-acquires it, but dereferences iso_pi(sk)->conn->hcon afterwards
without re-checking that conn is still valid.

While the lock is dropped, the connection can be torn down under the
same socket lock: iso_disconn_cfm() -> iso_conn_del() -> iso_chan_del()
sets iso_pi(sk)->conn to NULL (and the broadcast teardown path can also
clear conn->hcon on its own). When iso_conn_big_sync() re-acquires the
lock and reads conn->hcon, conn may be NULL, causing a NULL pointer
dereference (hcon is the first member of struct iso_conn).

This path is reached from iso_sock_recvmsg() for a PA-sync broadcast
sink socket (BT_SK_DEFER_SETUP | BT_SK_PA_SYNC), so the dropped-lock
window can race with connection teardown driven by controller events.

Re-validate iso_pi(sk)->conn and its hcon after re-acquiring the socket
lock and bail out if the connection went away, as already done in the
sibling iso_sock_rebind_bc().

Fixes: 7a17308c17880d ("Bluetooth: iso: Fix circular lock in iso_conn_big_sync")
Cc: stable@vger.kernel.org
Signed-off-by: Muhammad Bilal <meatuni001@gmail.com>
---
 net/bluetooth/iso.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/iso.c b/net/bluetooth/iso.c
index 3abd8111dda83..7186e8d88c757 100644
--- a/net/bluetooth/iso.c
+++ b/net/bluetooth/iso.c
@@ -1589,6 +1589,7 @@ static void iso_conn_big_sync(struct sock *sk)
 {
 	int err;
 	struct hci_dev *hdev;
+	struct iso_conn *conn;
 	bdaddr_t src, dst;
 	u8 src_type;
 
@@ -1611,8 +1612,17 @@ static void iso_conn_big_sync(struct sock *sk)
 	hci_dev_lock(hdev);
 	lock_sock(sk);
 
+	/* The socket lock was dropped for hci_get_route(), so the connection
+	 * may have been torn down meanwhile: iso_chan_del() clears conn and
+	 * the broadcast teardown path can clear conn->hcon on its own. Check
+	 * both before dereferencing conn->hcon.
+	 */
+	conn = iso_pi(sk)->conn;
+	if (!conn || !conn->hcon)
+		goto unlock;
+
 	if (!test_and_set_bit(BT_SK_BIG_SYNC, &iso_pi(sk)->flags)) {
-		err = hci_conn_big_create_sync(hdev, iso_pi(sk)->conn->hcon,
+		err = hci_conn_big_create_sync(hdev, conn->hcon,
 					       &iso_pi(sk)->qos,
 					       iso_pi(sk)->sync_handle,
 					       iso_pi(sk)->bc_num_bis,
@@ -1621,6 +1631,7 @@ static void iso_conn_big_sync(struct sock *sk)
 			bt_dev_err(hdev, "hci_big_create_sync: %d", err);
 	}
 
+unlock:
 	release_sock(sk);
 	hci_dev_unlock(hdev);
 	hci_dev_put(hdev);
-- 
2.54.0