linux-kernel - Re: [PATCH] staging: r8188eu: Fix PPPoE tag insertion on big endian systems

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Date:   Fri, 1 Apr 2022 13:40:21 -0500
From:   Larry Finger <Larry.Finger@...inger.net>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Phillip Potter <phil@...lpotter.co.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: r8188eu: Fix PPPoE tag insertion on big endian
 systems

On 4/1/22 10:12, Guenter Roeck wrote:
> In __nat25_add_pppoe_tag(), the tag length is read from the tag data
> structure. The value is kept in network format, but read as raw value.
> With -Warray-bounds, this results in the following gcc error/warning
> when building the driver on a big endian system such as alpha.
> 
> In function '__nat25_add_pppoe_tag',
>      inlined from 'nat25_db_handle' at
> 	drivers/staging/r8188eu/core/rtw_br_ext.c:479:11:
> arch/alpha/include/asm/string.h:22:16: error:
> 	'__builtin_memcpy' forming offset [40, 2051] is out of the bounds
> 	[0, 40] of object 'tag_buf' with type 'unsigned char[40]'
> 
> Add the missing ntohs().
> 
> Fixes: 15865124feed ("staging: r8188eu: introduce new core dir for RTL8188eu driver")
> Cc: Phillip Potter <phil@...lpotter.co.uk>
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> ---
>   drivers/staging/r8188eu/core/rtw_br_ext.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/r8188eu/core/rtw_br_ext.c b/drivers/staging/r8188eu/core/rtw_br_ext.c
> index d68611ef22f8..31bcd495ec04 100644
> --- a/drivers/staging/r8188eu/core/rtw_br_ext.c
> +++ b/drivers/staging/r8188eu/core/rtw_br_ext.c
> @@ -70,7 +70,7 @@ static int __nat25_add_pppoe_tag(struct sk_buff *skb, struct pppoe_tag *tag)
>   	struct pppoe_hdr *ph = (struct pppoe_hdr *)(skb->data + ETH_HLEN);
>   	int data_len;
>   
> -	data_len = tag->tag_len + TAG_HDR_LEN;
> +	data_len = htons(tag->tag_len) + TAG_HDR_LEN;
>   	if (skb_tailroom(skb) < data_len)
>   		return -1;
>   

Strange that a BE compiler would generate a warning for what is actually an 
execution error on LE platforms.

I prefer be16_to_cpu() to htons() as the former makes it clearer what is 
happening, but I suppose that is a matter of choice.

Reviewed_by: Larry Finger <Larry.Finger@...inger.net>

Incidentally, Sparse shows 3 more __be16 problems in this routine. I leave their 
fixing to you.

Larry