netdev - Re: [PATCH 1/1] mwifiex: Fix possible buffer overflows in mwifiex_uap_bss_param

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Date:   Tue, 08 Dec 2020 16:28:53 +0200
From:   Kalle Valo <kvalo@...eaurora.org>
To:     Xiaohui Zhang <ruc_zhangxiaohui@....com>
Cc:     Amitkumar Karwar <amitkarwar@...il.com>,
        Ganapathi Bhat <ganapathi.bhat@....com>,
        Xinming Hu <huxinming820@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] mwifiex: Fix possible buffer overflows in mwifiex_uap_bss_param_prepare

Xiaohui Zhang <ruc_zhangxiaohui@....com> writes:

> From: Zhang Xiaohui <ruc_zhangxiaohui@....com>
>
> mwifiex_uap_bss_param_prepare() 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 <ruc_zhangxiaohui@....com>
> ---
>  drivers/net/wireless/marvell/mwifiex/uap_cmd.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/wireless/marvell/mwifiex/uap_cmd.c b/drivers/net/wireless/marvell/mwifiex/uap_cmd.c
> index b48a85d79..fb937c7ee 100644
> --- a/drivers/net/wireless/marvell/mwifiex/uap_cmd.c
> +++ b/drivers/net/wireless/marvell/mwifiex/uap_cmd.c
> @@ -496,13 +496,16 @@ mwifiex_uap_bss_param_prepare(u8 *tlv, void *cmd_buf, u16 *param_size)
>  	struct mwifiex_ie_types_wmmcap *wmm_cap;
>  	struct mwifiex_uap_bss_param *bss_cfg = cmd_buf;
>  	int i;
> +	int ssid_size;
>  	u16 cmd_size = *param_size;
>  
>  	if (bss_cfg->ssid.ssid_len) {
>  		ssid = (struct host_cmd_tlv_ssid *)tlv;
>  		ssid->header.type = cpu_to_le16(TLV_TYPE_UAP_SSID);
>  		ssid->header.len = cpu_to_le16((u16)bss_cfg->ssid.ssid_len);
> -		memcpy(ssid->ssid, bss_cfg->ssid.ssid, bss_cfg->ssid.ssid_len);
> +		ssid_size = bss_cfg->ssid.ssid_len > strlen(ssid->ssid) ?
> +				strlen(ssid->ssid) : bss_cfg->ssid.ssid_len;
> +		memcpy(ssid->ssid, bss_cfg->ssid.ssid, ssid_size);

I think using min_t() is cleaner. Then you would not need to add a
temporary variable.

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