BMC/Intel-BMC/linux.git/net/ipv4/tcp_input.c, branch dev-4.3

tcp: fix zero cwnd in tcp_cwnd_reduction

2016-01-31T19:25:50+00:00

[ Upstream commit 8b8a321ff72c785ed5e8b4cf6eda20b35d427390 ] Patch 3759824da87b ("tcp: PRR uses CRB mode by default and SS mode conditionally") introduced a bug that cwnd may become 0 when both inflight and sndcnt are 0 (cwnd = inflight + sndcnt). This may lead to a div-by-zero if the connection starts another cwnd reduction phase by setting tp->prior_cwnd to the current cwnd (0) in tcp_init_cwnd_reduction(). To prevent this we skip PRR operation when nothing is acked or sacked. Then cwnd must be positive in all cases as long as ssthresh is positive: 1) The proportional reduction mode inflight > ssthresh > 0 2) The reduction bound mode a) inflight == ssthresh > 0 b) inflight < ssthresh sndcnt > 0 since newly_acked_sacked > 0 and inflight < ssthresh Therefore in all cases inflight and sndcnt can not both be 0. We check invalid tp->prior_cwnd to avoid potential div0 bugs. In reality this bug is triggered only with a sequence of less common events. For example, the connection is terminating an ECN-triggered cwnd reduction with an inflight 0, then it receives reordered/old ACKs or DSACKs from prior transmission (which acks nothing). Or the connection is in fast recovery stage that marks everything lost, but fails to retransmit due to local issues, then receives data packets from other end which acks nothing. Fixes: 3759824da87b ("tcp: PRR uses CRB mode by default and SS mode conditionally") Reported-by: Oleksandr Natalenko Signed-off-by: Yuchung Cheng Signed-off-by: Neal Cardwell Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman

tcp: initialize tp->copied_seq in case of cross SYN connection

2015-12-15T05:41:01+00:00

[ Upstream commit 142a2e7ece8d8ac0e818eb2c91f99ca894730e2a ] Dmitry provided a syzkaller (http://github.com/google/syzkaller) generated program that triggers the WARNING at net/ipv4/tcp.c:1729 in tcp_recvmsg() : WARN_ON(tp->copied_seq != tp->rcv_nxt && !(flags & (MSG_PEEK | MSG_TRUNC))); His program is specifically attempting a Cross SYN TCP exchange, that we support (for the pleasure of hackers ?), but it looks we lack proper tcp->copied_seq initialization. Thanks again Dmitry for your report and testings. Signed-off-by: Eric Dumazet Reported-by: Dmitry Vyukov Tested-by: Dmitry Vyukov Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman

tcp: fix potential huge kmalloc() calls in TCP_REPAIR

2015-12-15T05:41:01+00:00

[ Upstream commit 5d4c9bfbabdb1d497f21afd81501e5c54b0c85d9 ] tcp_send_rcvq() is used for re-injecting data into tcp receive queue. Problems : - No check against size is performed, allowed user to fool kernel in attempting very large memory allocations, eventually triggering OOM when memory is fragmented. - In case of fault during the copy we do not return correct errno. Lets use alloc_skb_with_frags() to cook optimal skbs. Fixes: 292e8d8c8538 ("tcp: Move rcvq sending to tcp_input.c") Fixes: c0e88ff0f256 ("tcp: Repair socket queues") Signed-off-by: Eric Dumazet Cc: Pavel Emelyanov Acked-by: Pavel Emelyanov Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman

tcp: use dctcp if enabled on the route to the initiator

2015-08-31T19:34:00+00:00

Currently, the following case doesn't use DCTCP, even if it should: A responder has f.e. Cubic as system wide default, but for a specific route to the initiating host, DCTCP is being set in RTAX_CC_ALGO. The initiating host then uses DCTCP as congestion control, but since the initiator sets ECT(0), tcp_ecn_create_request() doesn't set ecn_ok, and we have to fall back to Reno after 3WHS completes. We were thinking on how to solve this in a minimal, non-intrusive way without bloating tcp_ecn_create_request() needlessly: lets cache the CA ecn option flag in RTAX_FEATURES. In other words, when ECT(0) is set on the SYN packet, set ecn_ok=1 iff route RTAX_FEATURES contains the unexposed (internal-only) DST_FEATURE_ECN_CA. This allows to only do a single metric feature lookup inside tcp_ecn_create_request(). Joint work with Florian Westphal. Signed-off-by: Daniel Borkmann Signed-off-by: Florian Westphal Signed-off-by: David S. Miller

tcp: refine pacing rate determination

2015-08-25T18:33:54+00:00

When TCP pacing was added back in linux-3.12, we chose to apply a fixed ratio of 200 % against current rate, to allow probing for optimal throughput even during slow start phase, where cwnd can be doubled every other gRTT. At Google, we found it was better applying a different ratio while in Congestion Avoidance phase. This ratio was set to 120 %. We've used the normal tcp_in_slow_start() helper for a while, then tuned the condition to select the conservative ratio as soon as cwnd >= ssthresh/2 : - After cwnd reduction, it is safer to ramp up more slowly, as we approach optimal cwnd. - Initial ramp up (ssthresh == INFINITY) still allows doubling cwnd every other RTT. Signed-off-by: Eric Dumazet Cc: Neal Cardwell Cc: Yuchung Cheng Acked-by: Neal Cardwell Signed-off-by: David S. Miller

tcp: fix slow start after idle vs TSO/GSO

2015-08-25T18:22:50+00:00

slow start after idle might reduce cwnd, but we perform this after first packet was cooked and sent. With TSO/GSO, it means that we might send a full TSO packet even if cwnd should have been reduced to IW10. Moving the SSAI check in skb_entail() makes sense, because we slightly reduce number of times this check is done, especially for large send() and TCP Small queue callbacks from softirq context. As Neal pointed out, we also need to perform the check if/when receive window opens. Tested: Following packetdrill test demonstrates the problem // Test of slow start after idle `sysctl -q net.ipv4.tcp_slow_start_after_idle=1` 0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 +0 bind(3, ..., ...) = 0 +0 listen(3, 1) = 0 +0 < S 0:0(0) win 65535 +0 > S. 0:0(0) ack 1 +.100 < . 1:1(0) ack 1 win 511 +0 accept(3, ..., ...) = 4 +0 setsockopt(4, SOL_SOCKET, SO_SNDBUF, [200000], 4) = 0 +0 write(4, ..., 26000) = 26000 +0 > . 1:5001(5000) ack 1 +0 > . 5001:10001(5000) ack 1 +0 %{ assert tcpi_snd_cwnd == 10 }% +.100 < . 1:1(0) ack 10001 win 511 +0 %{ assert tcpi_snd_cwnd == 20, tcpi_snd_cwnd }% +0 > . 10001:20001(10000) ack 1 +0 > P. 20001:26001(6000) ack 1 +.100 < . 1:1(0) ack 26001 win 511 +0 %{ assert tcpi_snd_cwnd == 36, tcpi_snd_cwnd }% +4 write(4, ..., 20000) = 20000 // If slow start after idle works properly, we should send 5 MSS here (cwnd/2) +0 > . 26001:31001(5000) ack 1 +0 %{ assert tcpi_snd_cwnd == 10, tcpi_snd_cwnd }% +0 > . 31001:36001(5000) ack 1 Signed-off-by: Eric Dumazet Cc: Neal Cardwell Cc: Yuchung Cheng Acked-by: Neal Cardwell Signed-off-by: David S. Miller

Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net

2015-07-23T07:41:16+00:00

Conflicts: net/bridge/br_mdb.c br_mdb.c conflict was a function call being removed to fix a bug in 'net' but whose signature was changed in 'net-next'. Signed-off-by: David S. Miller

net: track success and failure of TCP PMTU probing

2015-07-22T05:36:33+00:00

Track success and failure of TCP PMTU probing. Signed-off-by: Rick Jones Signed-off-by: David S. Miller

tcp: don't use F-RTO on non-recurring timeouts

2015-07-16T00:17:21+00:00

Currently F-RTO may repeatedly send new data packets on non-recurring timeouts in CA_Loss mode. This is a bug because F-RTO (RFC5682) should only be used on either new recovery or recurring timeouts. This exacerbates the recovery progress during frequent timeout & repair, because we prioritize sending new data packets instead of repairing the holes when the bandwidth is already scarce. Fix it by correcting the test of a new recovery episode. Signed-off-by: Yuchung Cheng Signed-off-by: Neal Cardwell Signed-off-by: David S. Miller

tcp: update congestion state first before raising cwnd

2015-07-09T21:22:52+00:00

The congestion state and cwnd can be updated in the wrong order. For example, upon receiving a dubious ACK, we incorrectly raise the cwnd first (tcp_may_raise_cwnd()/tcp_cong_avoid()) because the state is still Open, then enter recovery state to reduce cwnd. For another example, if the ACK indicates spurious timeout or retransmits, we first revert the cwnd reduction and congestion state back to Open state. But we don't raise the cwnd even though the ACK does not indicate any congestion. To fix this problem we should first call tcp_fastretrans_alert() to process the dubious ACK and update the congestion state, then call tcp_may_raise_cwnd() that raises cwnd based on the current state. Signed-off-by: Yuchung Cheng Signed-off-by: Neal Cardwell Signed-off-by: Eric Dumazet Signed-off-by: Nandita Dukkipati Signed-off-by: David S. Miller