Re: [PATCH v1 1/1] l2tp: Use existing macros instead of literal number

On Fri, Aug 19, 2016 at 2:41 AM, Guillaume Nault [off-list ref] wrote:

On Thu, Aug 18, 2016 at 03:05:19PM +0800, fgao@ikuai8.com wrote:

quoted

From: Gao Feng <redacted>

1. Use PPP_ALLSTATIONS/PPP_UI instead of literal 0xff/0x03;
2. Use one static const global fixed_ppphdr instead of two same
static variable ppph in two different functions;
3. Use SEND_SHUTDOWN instead of literal 2;

Signed-off-by: Gao Feng <redacted>
---
 v1: Initial patch

No need to send 'v1' for the initial series.

OK, I get it.

quoted

--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c

@@ -138,6 +138,8 @@ static const struct ppp_channel_ops pppol2tp_chan_ops = {

 static const struct proto_ops pppol2tp_ops;

+static const unsigned char fixed_ppphdr[2] = {PPP_ALLSTATIONS, PPP_UI};
+
 /* Helpers to obtain tunnel/session contexts from sockets.
  */
 static inline struct l2tp_session *pppol2tp_sock_to_session(struct sock *sk)

@@ -174,11 +176,11 @@ static int pppol2tp_recv_payload_hook(struct sk_buff *skb)
       * Note that skb->data[] isn't dereferenced from a u16 ptr here since
       * the field may be unaligned.
       */
-     if (!pskb_may_pull(skb, 2))
+     if (!pskb_may_pull(skb, sizeof(fixed_ppphdr)))
              return 1;

-     if ((skb->data[0] == 0xff) && (skb->data[1] == 0x03))
-             skb_pull(skb, 2);
+     if ((PPP_ADDRESS(skb->data) == PPP_ALLSTATIONS) && (PPP_CONTROL(skb->data) == PPP_UI))
+             skb_pull(skb, sizeof(fixed_ppphdr));

Sorry, but I find the original code clearer. It's important to be
explicit about what's done with the sk_buff. Hiding skb->data[x] behind
macros certainly doesn't help.

Same thing for the use of sizeof(fixed_ppphdr) in pskb_may_pull(). The
size of fixed_ppphdr isn't used aftewards, so it's unclear why its size
was pulled. 2 was not a magic number here, it was directly related with
the operations done on the skb (i.e. accessing skb->data[0] and
skb->data[1]). So pskb_may_pull(skb, 2) makes perfect sense.

Agree now because of detail explanation.
Thanks.

OTOH, replacing 0xff and 0x03 with PPP_ALLSTATIONS and PPP_UI is fine.

OK. get it.

quoted

@@ -312,7 +313,7 @@ static int pppol2tp_sendmsg(struct socket *sock, struct msghdr *m,
      error = -ENOMEM;
      skb = sock_wmalloc(sk, NET_SKB_PAD + sizeof(struct iphdr) +
                         uhlen + session->hdr_len +
-                        sizeof(ppph) + total_len,
+                        sizeof(fixed_ppphdr) + total_len,
                         0, GFP_KERNEL);
      if (!skb)
              goto error_put_sess_tun;

@@ -325,9 +326,9 @@ static int pppol2tp_sendmsg(struct socket *sock, struct msghdr *m,
      skb_reserve(skb, uhlen);

      /* Add PPP header */
-     skb->data[0] = ppph[0];
-     skb->data[1] = ppph[1];
-     skb_put(skb, 2);
+     PPP_ADDRESS(skb->data) = fixed_ppphdr[0];
+     PPP_CONTROL(skb->data) = fixed_ppphdr[1];
+     skb_put(skb, sizeof(fixed_ppphdr));

Same here. What about
+ skb->data[0] = PPP_ALLSTATIONS;
+ skb->data[1] = PPP_UI;
+ skb_put(skb, 2);
and removing ppph entirely?

Agree with you.

quoted

      /* Copy user data into skb */
      error = memcpy_from_msg(skb_put(skb, total_len), m, total_len);

@@ -369,7 +370,6 @@ error:
  */
 static int pppol2tp_xmit(struct ppp_channel *chan, struct sk_buff *skb)
 {
-     static const u8 ppph[2] = { 0xff, 0x03 };
      struct sock *sk = (struct sock *) chan->private;
      struct sock *sk_tun;
      struct l2tp_session *session;

@@ -398,14 +398,14 @@ static int pppol2tp_xmit(struct ppp_channel *chan, struct sk_buff *skb)
                 sizeof(struct iphdr) + /* IP header */
                 uhlen +              /* UDP header (if L2TP_ENCAPTYPE_UDP) */
                 session->hdr_len +   /* L2TP header */
-                sizeof(ppph);        /* PPP header */
+                sizeof(fixed_ppphdr); /* PPP header */
      if (skb_cow_head(skb, headroom))
              goto abort_put_sess_tun;

      /* Setup PPP header */
-     __skb_push(skb, sizeof(ppph));
-     skb->data[0] = ppph[0];
-     skb->data[1] = ppph[1];
+     __skb_push(skb, sizeof(fixed_ppphdr));
+     skb->data[0] = fixed_ppphdr[0];
+     skb->data[1] = fixed_ppphdr[1];

Same as for pppol2tp_sendmsg().

quoted

@@ -440,7 +440,7 @@ static void pppol2tp_session_close(struct l2tp_session *session)
      BUG_ON(session->magic != L2TP_SESSION_MAGIC);

      if (sock) {
-             inet_shutdown(sock, 2);
+             inet_shutdown(sock, SEND_SHUTDOWN);

Ok.

Regards
Feng