On Sun, Aug 21, 2016 at 04:36:52PM -0600, Philp Prindeville wrote:
> Inline
>
>
> On 08/20/2016 09:52 AM, f...@48lvckh6395k16k5.yundunddos.com wrote:
> > From: Gao Feng <f...@ikuai8.com>
> >
> > Use PPP_ALLSTATIONS, PPP_UI, and SEND_SHUTDOWN instead of 0xff,
> > 0x03, and 2 separately.
> >
> > Signed-off-by: Gao Feng <f...@ikuai8.com>
> > ---
> > v3: Modify the subject;
> > v2: Only replace the literal number with macros according to Guillaume's
> > advice
> > v1: Inital patch
> >
> > net/l2tp/l2tp_ppp.c | 8 ++++----
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
> > index d9560aa..65e2fd6 100644
> > --- a/net/l2tp/l2tp_ppp.c
> > +++ b/net/l2tp/l2tp_ppp.c
> > @@ -177,7 +177,7 @@ static int pppol2tp_recv_payload_hook(struct sk_buff
> > *skb)
> > if (!pskb_may_pull(skb, 2))
> > return 1;
> > - if ((skb->data[0] == 0xff) && (skb->data[1] == 0x03))
> > + if ((skb->data[0] == PPP_ALLSTATIONS) && (skb->data[1] == PPP_UI))
>
> This should have used PPP_ADDRESS() and PPP_CONTROL() here.
>
Then please justify how would that make the code more readable.
We're not trying to interpret a known valid PPP header here.
> > skb_pull(skb, 2);
>
> This magic number should go away.
>
Again, this is *not* a magic number. We've explicitely accessed the
first _two_ header bytes and want to skip them.
pskb_may_pull(2), ->data[0], ->data[1] and skb_pull(2) all go together.
There's even a nice comment telling you what is done and why:
/* Skip PPP header, if present. In testing, Microsoft L2TP clients
* don't send the PPP header (PPP header compression enabled), but
* other clients can include the header. So we cope with both cases
* here. The PPP header is always FF03 when using L2TP.
*
* Note that skb->data[] isn't dereferenced from a u16 ptr here since
* the field may be unaligned.
*/
Apart from the unprecise "PPP header" term, which should be read as
"address and control fields", things should be quite clear.
> > @@ -282,7 +282,7 @@ static void pppol2tp_session_sock_put(struct
> > l2tp_session *session)
> > static int pppol2tp_sendmsg(struct socket *sock, struct msghdr *m,
> > size_t total_len)
> > {
> > - static const unsigned char ppph[2] = { 0xff, 0x03 };
> > + static const unsigned char ppph[2] = {PPP_ALLSTATIONS, PPP_UI};
>
> PPP has a 4-byte header. Where's the protocol value?
>
No, PPP header (whatever you include in it) is of variable length. And
the protocol has already been set by the PPP layer anyway.
We're in L2TP here.
