linux-kernel - Re: [PATCH v3] Bluetooth: btmtk: Fix null pointer when processing coredump

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Date:   Wed, 12 Jul 2023 08:11:41 +0200
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Chris Lu <chris.lu@...iatek.com>
Cc:     Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Von Dentz <luiz.dentz@...il.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Aaron Hou <aaron.hou@...iatek.com>,
        Steve Lee <steve.lee@...iatek.com>,
        linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v3] Bluetooth: btmtk: Fix null pointer when processing
 coredump

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@...iatek.com>
> Co-developed-by: Sean Wang <sean.wang@...iatek.com>
> Signed-off-by: Sean Wang <sean.wang@...iatek.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;
>   	}