path: root/net
diff options
authorThomas Graf <tgraf@suug.ch>2013-04-11 10:57:18 +0000
committerDavid S. Miller <davem@davemloft.net>2013-04-11 18:12:41 -0400
commit50bceae9bd3569d56744882f3012734d48a1d413 (patch)
tree3401f2bdfd0e502d78a8cbaad6c8f849b9dd8eba /net
parent7078b984223e0e0e17ecbf32bd05ef1a927c2788 (diff)
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>
Diffstat (limited to 'net')
1 files changed, 6 insertions, 2 deletions
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index b44cf81d817..509912a5ff9 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2388,8 +2388,12 @@ int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
TCP_SKB_CB(skb)->when = tcp_time_stamp;
- /* make sure skb->data is aligned on arches that require it */
- if (unlikely(NET_IP_ALIGN && ((unsigned long)skb->data & 3))) {
+ /* make sure skb->data is aligned on arches that require it
+ * and check if ack-trimming & collapsing extended the headroom
+ * beyond what csum_start can cover.
+ */
+ if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
+ skb_headroom(skb) >= 0xFFFF)) {
struct sk_buff *nskb = __pskb_copy(skb, MAX_TCP_HEADER,
return nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :