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SubjectRe: [PATCH v3] Bluetooth: btmtk: Fix null pointer when processing coredump
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Dear Chris,


Am 12.07.23 um 07:18 schrieb Chris Lu:
> There may be a potential null pointer risk if offset value is
> less than 0 when doing memcmp in btmtk_process_coredump().
> Checking offset is valid before doing memcmp.

Use imperative mood: Check offset …

> Signed-off-by: Chris Lu <chris.lu@mediatek.com>
> Co-developed-by: Sean Wang <sean.wang@mediatek.com>
> Signed-off-by: Sean Wang <sean.wang@mediatek.com>
> ---
> v2: fix typo
> v3: fix bot checking error
> ---
> drivers/bluetooth/btmtk.c | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/bluetooth/btmtk.c b/drivers/bluetooth/btmtk.c
> index 786f775196ae..0f290430ae0e 100644
> --- a/drivers/bluetooth/btmtk.c
> +++ b/drivers/bluetooth/btmtk.c
> @@ -370,7 +370,7 @@ EXPORT_SYMBOL_GPL(btmtk_register_coredump);
> int btmtk_process_coredump(struct hci_dev *hdev, struct sk_buff *skb)
> {
> struct btmediatek_data *data = hci_get_priv(hdev);
> - int err;
> + int err, offset;
>
> if (!IS_ENABLED(CONFIG_DEV_COREDUMP))
> return 0;
> @@ -392,15 +392,15 @@ int btmtk_process_coredump(struct hci_dev *hdev, struct sk_buff *skb)
> if (err < 0)
> break;
> data->cd_info.cnt++;
> + offset = skb->len - sizeof(MTK_COREDUMP_END);

For `sizeof()` shouldn’t you use `size_t`? But that is unsigned of
course. Maybe ssize_t then?

>
> /* Mediatek coredump data would be more than MTK_COREDUMP_NUM */
> - if (data->cd_info.cnt > MTK_COREDUMP_NUM &&
> - skb->len > sizeof(MTK_COREDUMP_END) &&
> - !memcmp((char *)&skb->data[skb->len - sizeof(MTK_COREDUMP_END)],
> - MTK_COREDUMP_END, sizeof(MTK_COREDUMP_END) - 1)) {
> - bt_dev_info(hdev, "Mediatek coredump end");
> - hci_devcd_complete(hdev);
> - }
> + if (data->cd_info.cnt > MTK_COREDUMP_NUM && offset > 0)

Why not keep it like before, and just add the condition `skb->len <
sizeof(MTK_COREDUMP_END)`? The compiler is probably going to optimize so
the value is not calculated twice.


Kind regards,

Paul


> + if (!memcmp((char *)&skb->data[offset], MTK_COREDUMP_END,
> + sizeof(MTK_COREDUMP_END) - 1)) {
> + bt_dev_info(hdev, "Mediatek coredump end");
> + hci_devcd_complete(hdev);
> + }
>
> break;
> }

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