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authorEric Dumazet <edumazet@google.com>2013-08-05 17:10:15 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-09-14 05:50:47 -0700
commit28e9a84cdf505686ac00ead1adcbc75f26b48487 (patch)
tree9253925b2adfd349b4bb2c74cadc601499e67bb6
parent45ff4d68f223419b7d77bc64cb4bbc0bc86c54d4 (diff)
tcp: cubic: fix overflow error in bictcp_update()
[ 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@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Neal Cardwell <ncardwell@google.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Stephen Hemminger <stephen@networkplumber.org> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--net/ipv4/tcp_cubic.c10
1 files changed, 6 insertions, 4 deletions
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index f376b05cca81..b9d22e62074b 100644
--- 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 bictcp *ca, u32 cwnd)
* 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;