tipc: fix skb truesize/datasize ratio control

In commit d618d09a68e4 ("tipc: enforce valid ratio between skb truesize
and contents") we introduced a test for ensuring that the condition
truesize/datasize <= 4 is true for a received buffer. Unfortunately this
test has two problems.

- Because of the integer arithmetics the test
  if (skb->truesize / buf_roundup_len(skb) > 4) will miss all
  ratios [4 < ratio < 5], which was not the intention.
- The buffer returned by skb_copy() inherits skb->truesize of the
  original buffer, which doesn't help the situation at all.

In this commit, we change the ratio condition and replace skb_copy()
with a call to skb_copy_expand() to finally get this right.

Acked-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 2 deletions

diff --git a/net/tipc/msg.c b/net/tipc/msg.c
index 55d8ba92291d..4e1c6f6450bb 100644
--- a/net/tipc/msg.c
+++ b/net/tipc/msg.c
@@ -208,8 +208,8 @@ bool tipc_msg_validate(struct sk_buff **_skb)
         int msz, hsz;
 
         /* Ensure that flow control ratio condition is satisfied */
-        if (unlikely(skb->truesize / buf_roundup_len(skb) > 4)) {
-                skb = skb_copy(skb, GFP_ATOMIC);
+        if (unlikely(skb->truesize / buf_roundup_len(skb) >= 4)) {
+                skb = skb_copy_expand(skb, BUF_HEADROOM, 0, GFP_ATOMIC);
                 if (!skb)
                         return false;
                 kfree_skb(*_skb);