tcp: Reallocate headroom if it would overflow csum_start
authorThomas Graf <tgraf@suug.ch>
Thu, 11 Apr 2013 10:57:18 +0000 (10:57 +0000)
committerDavid S. Miller <davem@davemloft.net>
Thu, 11 Apr 2013 22:12:41 +0000 (18:12 -0400)
commit50bceae9bd3569d56744882f3012734d48a1d413
tree3401f2bdfd0e502d78a8cbaad6c8f849b9dd8eba
parent7078b984223e0e0e17ecbf32bd05ef1a927c2788
tcp: Reallocate headroom if it would overflow csum_start

If a TCP retransmission gets partially ACKed and collapsed multiple
times it is possible for the headroom to grow beyond 64K which will
overflow the 16bit skb->csum_start which is based on the start of
the headroom. It has been observed rarely in the wild with IPoIB due
to the 64K MTU.

Verify if the acking and collapsing resulted in a headroom exceeding
what csum_start can cover and reallocate the headroom if so.

A big thank you to Jim Foraker <foraker1@llnl.gov> and the team at
LLNL for helping out with the investigation and testing.

Reported-by: Jim Foraker <foraker1@llnl.gov>
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
net/ipv4/tcp_output.c