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

[Guenter Roeck]

On 4/1/22 11:40, Larry Finger wrote:
> 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@xxxxxxxxxxxxxxxx>
> > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > ---
> >   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;

Wonder where my brain was. That should have been ntohs().

> >       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.
The rest of the code uses htons/ntohs, so I prefer to follow that lead.

> Reviewed_by: Larry Finger <Larry.Finger@xxxxxxxxxxxx>
>
> Incidentally, Sparse shows 3 more __be16 problems in this routine. I leave their fixing to you.

I'll need to resend anyway, so I'll track those down and fix them as well.

Thanks,
Guenter