tipc: let function tipc_msg_reverse() expand header when needed

The shortest TIPC message header, for cluster local CONNECTED messages,
is 24 bytes long. With this format, the fields "dest_node" and
"orig_node" are optimized away, since they in reality are redundant
in this particular case.

However, the absence of these fields leads to code inconsistencies
that are difficult to handle in some cases, especially when we need
to reverse or reject messages at the socket layer.

In this commit, we concentrate the handling of the absent fields
to one place, by letting the function tipc_msg_reverse() reallocate
the buffer and expand the header to 32 bytes when necessary. This
means that the socket code now can assume that the two previously
absent fields are present in the header when a message needs to be
rejected. This opens up for some further simplifications of the
socket code.

Reviewed-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 41 insertions, 26 deletions

diff --git a/net/tipc/msg.c b/net/tipc/msg.c
index 08b4cc7d496d..4339aab93034 100644
--- a/net/tipc/msg.c
+++ b/net/tipc/msg.c
@@ -463,43 +463,58 @@ bool tipc_msg_make_bundle(struct sk_buff **skb,  struct tipc_msg *msg,
 
 /**
  * tipc_msg_reverse(): swap source and destination addresses and add error code
- * @buf:  buffer containing message to be reversed
- * @dnode: return value: node where to send message after reversal
- * @err:  error code to be set in message
- * Consumes buffer if failure
+ * @own_node: originating node id for reversed message
+ * @skb:  buffer containing message to be reversed; may be replaced.
+ * @err:  error code to be set in message, if any
+ * Consumes buffer at failure
  * Returns true if success, otherwise false
  */
-bool tipc_msg_reverse(u32 own_addr,  struct sk_buff *buf, u32 *dnode,
-                      int err)
+bool tipc_msg_reverse(u32 own_node,  struct sk_buff **skb, u32 *dnode, int err)
 {
-        struct tipc_msg *msg = buf_msg(buf);
+        struct sk_buff *_skb = *skb;
+        struct tipc_msg *hdr = buf_msg(_skb);
         struct tipc_msg ohdr;
-        uint rdsz = min_t(uint, msg_data_sz(msg), MAX_FORWARD_SIZE);
+        int dlen = min_t(uint, msg_data_sz(hdr), MAX_FORWARD_SIZE);
 
-        if (skb_linearize(buf))
+        if (skb_linearize(_skb))
                 goto exit;
-        msg = buf_msg(buf);
-        if (msg_dest_droppable(msg))
+        hdr = buf_msg(_skb);
+        if (msg_dest_droppable(hdr))
                 goto exit;
-        if (msg_errcode(msg))
+        if (msg_errcode(hdr))
                 goto exit;
-        memcpy(&ohdr, msg, msg_hdr_sz(msg));
-        msg_set_errcode(msg, err);
-        msg_set_origport(msg, msg_destport(&ohdr));
-        msg_set_destport(msg, msg_origport(&ohdr));
-        msg_set_prevnode(msg, own_addr);
-        if (!msg_short(msg)) {
-                msg_set_orignode(msg, msg_destnode(&ohdr));
-                msg_set_destnode(msg, msg_orignode(&ohdr));
+
+        /* Take a copy of original header before altering message */
+        memcpy(&ohdr, hdr, msg_hdr_sz(hdr));
+
+        /* Never return SHORT header; expand by replacing buffer if necessary */
+        if (msg_short(hdr)) {
+                *skb = tipc_buf_acquire(BASIC_H_SIZE + dlen);
+                if (!*skb)
+                        goto exit;
+                memcpy((*skb)->data + BASIC_H_SIZE, msg_data(hdr), dlen);
+                kfree_skb(_skb);
+                _skb = *skb;
+                hdr = buf_msg(_skb);
+                memcpy(hdr, &ohdr, BASIC_H_SIZE);
+                msg_set_hdr_sz(hdr, BASIC_H_SIZE);
         }
-        msg_set_size(msg, msg_hdr_sz(msg) + rdsz);
-        skb_trim(buf, msg_size(msg));
-        skb_orphan(buf);
-        *dnode = msg_orignode(&ohdr);
+
+        /* Now reverse the concerned fields */
+        msg_set_errcode(hdr, err);
+        msg_set_origport(hdr, msg_destport(&ohdr));
+        msg_set_destport(hdr, msg_origport(&ohdr));
+        msg_set_destnode(hdr, msg_prevnode(&ohdr));
+        msg_set_prevnode(hdr, own_node);
+        msg_set_orignode(hdr, own_node);
+        msg_set_size(hdr, msg_hdr_sz(hdr) + dlen);
+        *dnode = msg_destnode(hdr);
+        skb_trim(_skb, msg_size(hdr));
+        skb_orphan(_skb);
         return true;
 exit:
-        kfree_skb(buf);
-        *dnode = 0;
+        kfree_skb(_skb);
+        *skb = NULL;
         return false;
 }