Subject: Re: [PATCH 1/1] mwifiex: Fix possible buffer overflows in mwifiex_config_scan

From: Peter Seiderer <[email-masked]>
Date: Sat, 9 Jan 2021 16:08:44 +0100

Hello Zhang,

On Tue,  8 Dec 2020 20:45:23 +0800, Xiaohui Zhang <[email-masked]> wrote:

> From: Zhang Xiaohui <[email-masked]>
>
> mwifiex_config_scan() calls memcpy() without checking
> the destination size may trigger a buffer overflower,
> which a local user could use to cause denial of service
> or the execution of arbitrary code.
> Fix it by putting the length check before calling memcpy().
>
> Signed-off-by: Zhang Xiaohui <[email-masked]>
> ---
>  drivers/net/wireless/marvell/mwifiex/scan.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/net/wireless/marvell/mwifiex/scan.c b/drivers/net/wireless/marvell/mwifiex/scan.c
> index c2a685f63..b1d90678f 100644
> --- a/drivers/net/wireless/marvell/mwifiex/scan.c
> +++ b/drivers/net/wireless/marvell/mwifiex/scan.c
> @@ -930,6 +930,8 @@ mwifiex_config_scan(struct mwifiex_private *priv,
>  				    "DIRECT-", 7))
>  				wildcard_ssid_tlv->max_ssid_length = 0xfe;
>
> +			if (ssid_len > 1)
> +				ssid_len = 1;

Why do your believe the available size is only '1'? A SSID is expected
to be of size IEEE80211_MAX_SSID_LE/32 and the wildcard_ssid_tlv pointer
is casted from tlv_pos (some lines above) which is a pointer/index into
scan_cfg_out->tlv_buf...

And the define (line 44) indicates there should be enough space for a SSID:

  42 /* Memory needed to store a max number/size WildCard SSID TLV for a firmware
  43         scan */
  44 #define WILDCARD_SSID_TLV_MAX_SIZE  \
  45         (MWIFIEX_MAX_SSID_LIST_LENGTH *                                 \
  46                 (sizeof(struct mwifiex_ie_types_wildcard_ssid_params)   \
  47                         + IEEE80211_MAX_SSID_LEN))

For sure something to improve here instead of using a confusing 'u8 ssid[1]'
in struct mwifiex_ie_types_wildcard_ssid_params...

Regards,
Peter

>  			memcpy(wildcard_ssid_tlv->ssid,
>  			       user_scan_in->ssid_list[i].ssid, ssid_len);
>