This is a note to let you know that I've just added the patch titled
tcp: Reallocate headroom if it would overflow csum_start
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tcp-reallocate-headroom-if-it-would-overflow-csum_start.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 2527557a08f9d60e9fd38737b5a029b480af50bd Mon Sep 17 00:00:00 2001
From: Thomas Graf <[email protected]>
Date: Thu, 11 Apr 2013 10:57:18 +0000
Subject: tcp: Reallocate headroom if it would overflow csum_start
From: Thomas Graf <[email protected]>
[ Upstream commit 50bceae9bd3569d56744882f3012734d48a1d413 ]
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 <[email protected]> and the team at
LLNL for helping out with the investigation and testing.
Reported-by: Jim Foraker <[email protected]>
Signed-off-by: Thomas Graf <[email protected]>
Acked-by: Eric Dumazet <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
net/ipv4/tcp_output.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2154,8 +2154,12 @@ int tcp_retransmit_skb(struct sock *sk,
*/
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,
GFP_ATOMIC);
err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
Patches currently in stable-queue which might be from [email protected] are
queue-3.4/tcp-reallocate-headroom-if-it-would-overflow-csum_start.patch
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