tipc: reassign pointers after skb reallocation / linearization

In tipc_msg_reverse(), we assign skb attributes to local pointers
in stack at startup. This is followed by skb_linearize() and for
cloned buffers we perform skb relocation using pskb_expand_head().
Both these methods may update the skb attributes and thus making
the pointers incorrect.

In this commit, we fix this error by ensuring that the pointers
are re-assigned after any of these skb operations.

Fixes: 29042e19f2c60 ("tipc: let function tipc_msg_reverse() expand header
when needed")
Signed-off-by: Parthasarathy Bhuvaragan <parthasarathy.bhuvaragan@ericsson.com>
Reviewed-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/msg.c

@@ -479,13 +479,14 @@ bool tipc_msg_make_bundle(struct sk_buff **skb,  struct tipc_msg *msg,
 bool tipc_msg_reverse(u32 own_node,  struct sk_buff **skb, int err)
 {
 	struct sk_buff *_skb = *skb;
-	struct tipc_msg *hdr = buf_msg(_skb);
+	struct tipc_msg *hdr;
 	struct tipc_msg ohdr;
-	int dlen = min_t(uint, msg_data_sz(hdr), MAX_FORWARD_SIZE);
+	int dlen;
 
 	if (skb_linearize(_skb))
 		goto exit;
 	hdr = buf_msg(_skb);
+	dlen = min_t(uint, msg_data_sz(hdr), MAX_FORWARD_SIZE);
 	if (msg_dest_droppable(hdr))
 		goto exit;
 	if (msg_errcode(hdr))
@@ -511,6 +512,8 @@ bool tipc_msg_reverse(u32 own_node,  struct sk_buff **skb, int err)
 	    pskb_expand_head(_skb, BUF_HEADROOM, BUF_TAILROOM, GFP_ATOMIC))
 		goto exit;
 
+	/* reassign after skb header modifications */
+	hdr = buf_msg(_skb);
 	/* Now reverse the concerned fields */
 	msg_set_errcode(hdr, err);
 	msg_set_non_seq(hdr, 0);