Re: [PATCH] Bluetooth: hci_sync: fix stack buffer overflow in hci_le_big_create_sync

Paul Menzel
2026-03-31T06:29:13Z

Dear hkbinbin,

Thank you for your patch. It’d be great if you spelt your name with
capital letters and spaces (`git config --global user.name "…"`).

Am 31.03.26 um 07:39 schrieb hkbinbin:
> hci_le_big_create_sync() uses DEFINE_FLEX to allocate a
> struct hci_cp_le_big_create_sync on the stack with room for 0x11 (17)
> BIS entries. However, conn->num_bis can hold up to HCI_MAX_ISO_BIS (31)
> entries — validated against ISO_MAX_NUM_BIS (0x1f) in the caller
> hci_conn_big_create_sync(). When conn->num_bis is between 18 and 31,
> the memcpy that copies conn->bis into cp->bis writes up to 14 bytes
> past the stack buffer, corrupting adjacent stack memory.
>
> This is trivially reproducible: binding an ISO socket with
> bc_num_bis = ISO_MAX_NUM_BIS (31) and calling listen() will

If this is not more than twenty lines, maybe share the program/script?

> eventually trigger hci_le_big_create_sync() from the HCI command
> sync worker, causing a KASAN-detectable stack-out-of-bounds write:
>
> BUG: KASAN: stack-out-of-bounds in hci_le_big_create_sync+0x256/0x3b0
> Write of size 31 at addr ffffc90000487b48 by task kworker/u9:0/71
>
> Fix this by changing the DEFINE_FLEX count from the incorrect 0x11 to
> HCI_MAX_ISO_BIS, which matches the maximum number of BIS entries that
> conn->bis can actually carry.
>
> Fixes: 42ecf1947135 ("Bluetooth: ISO: Do not emit LE BIG Create Sync if previous is pending")

Just for the record, that the commit is present since Linux v6.13-rc1.

> Cc: stable@vger.kernel.org
> Signed-off-by: hkbinbin <hkbinbinbin@gmail.com>
> ---
> net/bluetooth/hci_sync.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
> index 45d16639874a..b84587061ae0 100644
> --- a/net/bluetooth/hci_sync.c
> +++ b/net/bluetooth/hci_sync.c
> @@ -7222,7 +7222,8 @@ static void create_big_complete(struct hci_dev *hdev, void *data, int err)
>
> static int hci_le_big_create_sync(struct hci_dev *hdev, void *data)
> {
> - DEFINE_FLEX(struct hci_cp_le_big_create_sync, cp, bis, num_bis, 0x11);
> + DEFINE_FLEX(struct hci_cp_le_big_create_sync, cp, bis, num_bis,
> + HCI_MAX_ISO_BIS);
> struct hci_conn *conn = data;
> struct bt_iso_qos *qos = &conn->iso_qos;
> int err;

The diff looks good. Great find.

Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>

Kind regards,

Paul