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

[Brian Norris <briannorris@chromium.org>]

On Tue, Dec 8, 2020 at 7:14 AM Xiaohui Zhang <ruc_zhangxiaohui@163.com> wrote:
>
> From: Zhang Xiaohui <ruc_zhangxiaohui@163.com>
>
> 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().

^^ That's not really what you're doing any more, for the record. But
then, describing "what" is not really the point of a commit message
(that's what the code is for), so maybe that's not that important.

> Signed-off-by: Zhang Xiaohui <ruc_zhangxiaohui@163.com>
> ---
>  drivers/net/wireless/marvell/mwifiex/scan.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/wireless/marvell/mwifiex/scan.c b/drivers/net/wireless/marvell/mwifiex/scan.c
> index c2a685f63..34293fd80 100644
> --- a/drivers/net/wireless/marvell/mwifiex/scan.c
> +++ b/drivers/net/wireless/marvell/mwifiex/scan.c
> @@ -931,7 +931,7 @@ mwifiex_config_scan(struct mwifiex_private *priv,
>                                 wildcard_ssid_tlv->max_ssid_length = 0xfe;
>
>                         memcpy(wildcard_ssid_tlv->ssid,
> -                              user_scan_in->ssid_list[i].ssid, ssid_len);
> +                              user_scan_in->ssid_list[i].ssid, min_t(u32, ssid_len, 1));

This *looks* like it should be wrong, because SSIDs are clearly longer
than 1 byte in many cases, but you *are* right that this is what the
struct is defined as:

struct mwifiex_ie_types_wildcard_ssid_params {
...
    u8 ssid[1];
};

This feels like something that could use some confirmation from
NXP/ex-Marvell folks if possible, but if not that, at least some
creative testing. Did you actually test this patch, to make sure
non-wildcard scans still work?

Also, even if this is correct, it seems like it would be more correct
to use 'sizeof(wildcard_ssid_tlv->ssid)' instead of a magic number 1.

Brian

>
>                         tlv_pos += (sizeof(wildcard_ssid_tlv->header)
>                                 + le16_to_cpu(wildcard_ssid_tlv->header.len));
> --
> 2.17.1
>