Re: [PATCH] Bluetooth: Fix skb allocation in mgmt_remote_name()

[Luiz Augusto von Dentz]

Hi Radoslaw,

On Thu, Jan 13, 2022 at 7:09 AM Radoslaw Biernacki <rad@xxxxxxxxxxxx> wrote:
>
> From: Radoslaw Biernacki <rad@xxxxxxxxxxxx>
>
> This patch fixes skb allocation, as lack of space for ev might push skb
> tail beyond its end.
> Also introduce eir_precalc_len() that can be used instead of magic
> numbers for similar eir operations on skb.
>
> Fixes: cf1bce1de7eeb ("Bluetooth: mgmt: Make use of mgmt_send_event_skb in MGMT_EV_DEVICE_FOUND")
> Signed-off-by: Angela Czubak <acz@xxxxxxxxxxxx>
> Signed-off-by: Marek Maslanka <mm@xxxxxxxxxxxx>
> Signed-off-by: Radoslaw Biernacki <rad@xxxxxxxxxxxx>
> ---
>  net/bluetooth/eir.h  |  5 +++++
>  net/bluetooth/mgmt.c | 12 ++++--------
>  2 files changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/net/bluetooth/eir.h b/net/bluetooth/eir.h
> index 05e2e917fc25..e5876751f07e 100644
> --- a/net/bluetooth/eir.h
> +++ b/net/bluetooth/eir.h
> @@ -15,6 +15,11 @@ u8 eir_create_scan_rsp(struct hci_dev *hdev, u8 instance, u8 *ptr);
>  u8 eir_append_local_name(struct hci_dev *hdev, u8 *eir, u8 ad_len);
>  u8 eir_append_appearance(struct hci_dev *hdev, u8 *ptr, u8 ad_len);
>
> +static inline u16 eir_precalc_len(u8 data_len)
> +{
> +       return sizeof(u8) * 2 + data_len;
> +}
> +
>  static inline u16 eir_append_data(u8 *eir, u16 eir_len, u8 type,
>                                   u8 *data, u8 data_len)
>  {
> diff --git a/net/bluetooth/mgmt.c b/net/bluetooth/mgmt.c
> index 37087cf7dc5a..d517fd847730 100644
> --- a/net/bluetooth/mgmt.c
> +++ b/net/bluetooth/mgmt.c
> @@ -9680,13 +9680,11 @@ void mgmt_remote_name(struct hci_dev *hdev, bdaddr_t *bdaddr, u8 link_type,
>  {
>         struct sk_buff *skb;
>         struct mgmt_ev_device_found *ev;
> -       u16 eir_len;
> -       u32 flags;
> +       u16 eir_len = 0;
> +       u32 flags = 0;
>
> -       if (name_len)
> -               skb = mgmt_alloc_skb(hdev, MGMT_EV_DEVICE_FOUND, 2 + name_len);
> -       else
> -               skb = mgmt_alloc_skb(hdev, MGMT_EV_DEVICE_FOUND, 0);
> +       skb = mgmt_alloc_skb(hdev, MGMT_EV_DEVICE_FOUND,
> +                            sizeof(*ev) + (name ? eir_precalc_len(name_len) : 0));

Looks like mgmt_device_connected also has a similar problem.

>         ev = skb_put(skb, sizeof(*ev));
>         bacpy(&ev->addr.bdaddr, bdaddr);
> @@ -9696,10 +9694,8 @@ void mgmt_remote_name(struct hci_dev *hdev, bdaddr_t *bdaddr, u8 link_type,
>         if (name) {
>                 eir_len = eir_append_data(ev->eir, 0, EIR_NAME_COMPLETE, name,
>                                           name_len);
> -               flags = 0;
>                 skb_put(skb, eir_len);
>         } else {
> -               eir_len = 0;
>                 flags = MGMT_DEV_FOUND_NAME_REQUEST_FAILED;
>         }

These changes would leave flags and eir_len uninitialized.

> --
> 2.34.1.703.g22d0c6ccf7-goog
>


-- 
Luiz Augusto von Dentz