linux.git/net/ipv4/tcp_input.c, branch v4.12

tcp: eliminate negative reordering in tcp_clean_rtx_queue

2017-05-16T16:45:21+00:00

tcp_ack() can call tcp_fragment() which may dededuct the
value tp->fackets_out when MSS changes. When prior_fackets
is larger than tp->fackets_out, tcp_clean_rtx_queue() can
invoke tcp_update_reordering() with negative values. This
results in absurd tp->reodering values higher than
sysctl_tcp_max_reordering.

Note that tcp_update_reordering indeeds sets tp->reordering
to min(sysctl_tcp_max_reordering, metric), but because
the comparison is signed, a negative metric always wins.

Fixes: c7caf8d3ed7a ("[TCP]: Fix reord detection due to snd_una covered holes")
Reported-by: Rebecca Isaacs 
Signed-off-by: Soheil Hassas Yeganeh 
Signed-off-by: Neal Cardwell 
Signed-off-by: Yuchung Cheng 
Signed-off-by: Eric Dumazet 
Signed-off-by: David S. Miller

tcp: avoid fragmenting peculiar skbs in SACK

2017-05-12T01:35:20+00:00

This patch fixes a bug in splitting an SKB during SACK
processing. Specifically if an skb contains multiple
packets and is only partially sacked in the higher sequences,
tcp_match_sack_to_skb() splits the skb and marks the second fragment
as SACKed.

The current code further attempts rounding up the first fragment
to MSS boundaries. But it misses a boundary condition when the
rounded-up fragment size (pkt_len) is exactly skb size.  Spliting
such an skb is pointless and causses a kernel warning and aborts
the SACK processing. This patch universally checks such over-split
before calling tcp_fragment to prevent these unnecessary warnings.

Fixes: adb92db857ee ("tcp: Make SACK code to split only at mss boundaries")
Signed-off-by: Yuchung Cheng 
Signed-off-by: Eric Dumazet 
Signed-off-by: Soheil Hassas Yeganeh 
Acked-by: Neal Cardwell 
Signed-off-by: David S. Miller

tcp: randomize timestamps on syncookies

2017-05-05T16:00:11+00:00

Whole point of randomization was to hide server uptime, but an attacker
can simply start a syn flood and TCP generates 'old style' timestamps,
directly revealing server jiffies value.

Also, TSval sent by the server to a particular remote address vary
depending on syncookies being sent or not, potentially triggering PAWS
drops for innocent clients.

Lets implement proper randomization, including for SYNcookies.

Also we do not need to export sysctl_tcp_timestamps, since it is not
used from a module.

In v2, I added Florian feedback and contribution, adding tsoff to
tcp_get_cookie_sock().

v3 removed one unused variable in tcp_v4_connect() as Florian spotted.

Fixes: 95a22caee396c ("tcp: randomize tcp timestamp offsets for each connection")
Signed-off-by: Eric Dumazet 
Reviewed-by: Florian Westphal 
Tested-by: Florian Westphal 
Cc: Yuchung Cheng 
Signed-off-by: David S. Miller

tcp: switch rcv_rtt_est and rcvq_space to high resolution timestamps

2017-04-26T18:44:39+00:00

Some devices or distributions use HZ=100 or HZ=250

TCP receive buffer autotuning has poor behavior caused by this choice.
Since autotuning happens after 4 ms or 10 ms, short distance flows
get their receive buffer tuned to a very high value, but after an initial
period where it was frozen to (too small) initial value.

With tp->tcp_mstamp introduction, we can switch to high resolution
timestamps almost for free (at the expense of 8 additional bytes per
TCP structure)

Note that some TCP stacks use usec TCP timestamps where this
patch makes even more sense : Many TCP flows have < 500 usec RTT.
Hopefully this finer TS option can be standardized soon.

Tested:
 HZ=100 kernel
 ./netperf -H lpaa24 -t TCP_RR -l 1000 -- -r 10000,10000 &

 Peer without patch :
 lpaa24:~# ss -tmi dst lpaa23
 ...
 skmem:(r0,rb8388608,...)
 rcv_rtt:10 rcv_space:3210000 minrtt:0.017

 Peer with the patch :
 lpaa23:~# ss -tmi dst lpaa24
 ...
 skmem:(r0,rb428800,...)
 rcv_rtt:0.069 rcv_space:30000 minrtt:0.017

We can see saner RCVBUF, and more precise rcv_rtt information.

Signed-off-by: Eric Dumazet 
Acked-by: Soheil Hassas Yeganeh 
Acked-by: Neal Cardwell 
Signed-off-by: David S. Miller

tcp: remove ack_time from struct tcp_sacktag_state

2017-04-26T18:44:38+00:00

It is no longer needed, everything uses tp->tcp_mstamp instead.

Signed-off-by: Eric Dumazet 
Acked-by: Soheil Hassas Yeganeh 
Acked-by: Neal Cardwell 
Signed-off-by: David S. Miller

tcp: use tp->tcp_mstamp in tcp_clean_rtx_queue()

2017-04-26T18:44:38+00:00

Following patch will remove ack_time from struct tcp_sacktag_state

Same info is now found in tp->tcp_mstamp

Signed-off-by: Eric Dumazet 
Acked-by: Soheil Hassas Yeganeh 
Acked-by: Neal Cardwell 
Signed-off-by: David S. Miller

tcp: do not pass timestamp to tcp_rack_advance()

2017-04-26T18:44:38+00:00

No longer needed, since tp->tcp_mstamp holds the information.

This is needed to remove sack_state.ack_time in a following patch.

Signed-off-by: Eric Dumazet 
Acked-by: Soheil Hassas Yeganeh 
Acked-by: Neal Cardwell 
Signed-off-by: David S. Miller

tcp: do not pass timestamp to tcp_rate_gen()

2017-04-26T18:44:38+00:00

No longer needed, since tp->tcp_mstamp holds the information.

This is needed to remove sack_state.ack_time in a following patch.

Signed-off-by: Eric Dumazet 
Acked-by: Soheil Hassas Yeganeh 
Acked-by: Neal Cardwell 
Signed-off-by: David S. Miller

tcp: do not pass timestamp to tcp_fastretrans_alert()

2017-04-26T18:44:38+00:00

Not used anymore now tp->tcp_mstamp holds the information.

This is needed to remove sack_state.ack_time in a following patch.

Signed-off-by: Eric Dumazet 
Acked-by: Soheil Hassas Yeganeh 
Acked-by: Neal Cardwell 
Signed-off-by: David S. Miller

tcp: do not pass timestamp to tcp_rack_identify_loss()

2017-04-26T18:44:37+00:00

Not used anymore now tp->tcp_mstamp holds the information.

Signed-off-by: Eric Dumazet 
Acked-by: Soheil Hassas Yeganeh 
Acked-by: Neal Cardwell 
Signed-off-by: David S. Miller