Patch "tcp: cubic: fix overflow error in bictcp_update()" has been added to the 3.10-stable tree

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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 3.10-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-3.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 68e2de5cd376e7c693ac22b22c2f65ca23a1a9df 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
@@ -206,8 +206,8 @@ 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 */
 
@@ -250,9 +250,11 @@ 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-3.10/ip_gre-fix-ipgre_header-to-return-correct-offset-mime-version-1.0.patch
queue-3.10/tcp-cubic-fix-overflow-error-in-bictcp_update.patch
queue-3.10/tcp-cubic-fix-bug-in-bictcp_acked.patch
queue-3.10/net-revert-8728c544a9c-net-dev_pick_tx-fix.patch
queue-3.10/net-ipv6-tcp-fix-potential-use-after-free-in-tcp_v6_do_rcv.patch
queue-3.10/net-check-net.core.somaxconn-sysctl-values.patch
queue-3.10/htb-fix-sign-extension-bug.patch
queue-3.10/fib_trie-remove-potential-out-of-bound-access.patch
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