This is a note to let you know that I've just added the patch titled
tcp: cubic: fix overflow error in bictcp_update()
to the 3.0-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-cubic-fix-overflow-error-in-bictcp_update.patch
and it can be found in the queue-3.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 2a2d16df60d3c8d4ac6409026c120d38f00c9ea5 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@xxxxxxxxxx>
Date: Mon, 5 Aug 2013 17:10:15 -0700
Subject: tcp: cubic: fix overflow error in bictcp_update()
From: Eric Dumazet <edumazet@xxxxxxxxxx>
[ Upstream commit 2ed0edf9090bf4afa2c6fc4f38575a85a80d4b20 ]
commit 17a6e9f1aa9 ("tcp_cubic: fix clock dependency") added an
overflow error in bictcp_update() in following code :
/* change the unit from HZ to bictcp_HZ */
t = ((tcp_time_stamp + msecs_to_jiffies(ca->delay_min>>3) -
ca->epoch_start) << BICTCP_HZ) / HZ;
Because msecs_to_jiffies() being unsigned long, compiler does
implicit type promotion.
We really want to constrain (tcp_time_stamp - ca->epoch_start)
to a signed 32bit value, or else 't' has unexpected high values.
This bugs triggers an increase of retransmit rates ~24 days after
boot [1], as the high order bit of tcp_time_stamp flips.
[1] for hosts with HZ=1000
Big thanks to Van Jacobson for spotting this problem.
Diagnosed-by: Van Jacobson <vanj@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Neal Cardwell <ncardwell@xxxxxxxxxx>
Cc: Yuchung Cheng <ycheng@xxxxxxxxxx>
Cc: Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx>
Acked-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/ipv4/tcp_cubic.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -204,8 +204,8 @@ static u32 cubic_root(u64 a)
*/
static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
{
- u64 offs;
- u32 delta, t, bic_target, max_cnt;
+ u32 delta, bic_target, max_cnt;
+ u64 offs, t;
ca->ack_cnt++; /* count the number of ACKs */
@@ -248,9 +248,11 @@ static inline void bictcp_update(struct
* if the cwnd < 1 million packets !!!
*/
+ t = (s32)(tcp_time_stamp - ca->epoch_start);
+ t += msecs_to_jiffies(ca->delay_min >> 3);
/* change the unit from HZ to bictcp_HZ */
- t = ((tcp_time_stamp + msecs_to_jiffies(ca->delay_min>>3)
- - ca->epoch_start) << BICTCP_HZ) / HZ;
+ t <<= BICTCP_HZ;
+ do_div(t, HZ);
if (t < ca->bic_K) /* t - K */
offs = ca->bic_K - t;
Patches currently in stable-queue which might be from edumazet@xxxxxxxxxx are
queue-3.0/fib_trie-remove-potential-out-of-bound-access.patch
queue-3.0/net-check-net.core.somaxconn-sysctl-values.patch
queue-3.0/tcp-cubic-fix-bug-in-bictcp_acked.patch
queue-3.0/tcp-cubic-fix-overflow-error-in-bictcp_update.patch
queue-3.0/htb-fix-sign-extension-bug.patch
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