[TCP]: Compute in_sacked properly when we split up a TSO frame.

The problem is that the SACK fragmenting code may incorrectly call
tcp_fragment() with a length larger than the skb->len.  This happens
when the skb on the transmit queue completely falls to the LHS of the
SACK.

And add a BUG() check to tcp_fragment() so we can spot this kind of
error more quickly in the future.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index c10e4435e3b1..b018e31b6530 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -435,6 +435,8 @@ int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len, unsigned int mss
         int nsize, old_factor;
         u16 flags;
 
+        BUG_ON(len >= skb->len);
+
         nsize = skb_headlen(skb) - len;
         if (nsize < 0)
                 nsize = 0;