BMC/Intel-BMC/linux.git/net/ipv4/sysctl_net_ipv4.c, branch dev

Revert "net: limit tcp/udp rmem/wmem to SOCK_{RCV,SND}BUF_MIN"

2015-08-17T19:10:30+00:00

Commit 8133534c760d4083 ("net: limit tcp/udp rmem/wmem to SOCK_{RCV,SND}BUF_MIN") modified four sysctls to enforce that the values written to them are not less than SOCK_MIN_{RCV,SND}BUF. That change causes 4096 to no longer be accepted as a valid value for 'min' in tcp_wmem and udp_wmem_min. 4096 has been the default for both of those sysctls for a long time, and unfortunately seems to be an extremely popular setting. This change breaks a large number of sysctl configurations at Facebook. That commit referred to b1cb59cf2efe7971 ("net: sysctl_net_core: check SNDBUF and RCVBUF for min length"), which choose to use the SOCK_MIN constants as the lower limits to avoid nasty bugs. But AFAICS, a limit of SOCK_MIN_SNDBUF isn't necessary to do that: the BUG_ON cited in the commit message seems to have happened because unix_stream_sendmsg() expects a minimum of a full page (ie SK_MEM_QUANTUM) and the math broke, not because it had less than SOCK_MIN_SNDBUF allocated. This particular issue doesn't seem to affect TCP however: using a setting of "1 1 1" for tcp_{r,w}mem works, although it's obviously suboptimal. SK_MEM_QUANTUM would be a nice minimum, but it's 64K on some archs, so there would still be breakage. Since a value of one doesn't seem to cause any problems, we can drop the minimum 8133534c added to fix this. This reverts commit 8133534c760d4083f79d2cde42c636ccc0b2792e. Fixes: 8133534c760d4083 ("net: limit tcp/udp rmem/wmem to SOCK_MIN...") Cc: Eric Dumazet Cc: Sorin Dumitru Signed-off-by: Calvin Owens Acked-by: Eric Dumazet Signed-off-by: David S. Miller

net: limit tcp/udp rmem/wmem to SOCK_{RCV,SND}BUF_MIN

2015-05-31T00:37:44+00:00

This is similar to b1cb59cf2efe(net: sysctl_net_core: check SNDBUF and RCVBUF for min length). I don't think too small values can cause crashes in the case of udp and tcp, but I've seen this set to too small values which triggered awful performance. It also makes the setting consistent across all the wmem/rmem sysctls. Signed-off-by: Sorin Dumitru Signed-off-by: David S. Miller

tcp/dccp: warn user for preferred ip_local_port_range

2015-05-27T18:35:36+00:00

After commit 07f4c90062f8f ("tcp/dccp: try to not exhaust ip_local_port_range in connect()") it is advised to have an even number of ports described in /proc/sys/net/ipv4/ip_local_port_range This means start/end values should have a different parity. Let's warn sysadmins of this, so that they can update their settings if they want to. Suggested-by: David S. Miller Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: tcp_tso_autosize() minimum is one packet

2015-05-27T03:21:29+00:00

By making sure sk->sk_gso_max_segs minimal value is one, and sysctl_tcp_min_tso_segs minimal value is one as well, tcp_tso_autosize() will return a non zero value. We can then revert 843925f33fcc293d80acf2c5c8a78adf3344d49b ("tcp: Do not apply TSO segment limit to non-TSO packets") and save few cpu cycles in fast path. Signed-off-by: Eric Dumazet Cc: Neal Cardwell Cc: Herbert Xu Acked-by: Neal Cardwell Acked-by: Herbert Xu Signed-off-by: David S. Miller

tcp: add rfc3168, section 6.1.1.1. fallback

2015-05-19T20:53:37+00:00

This work as a follow-up of commit f7b3bec6f516 ("net: allow setting ecn via routing table") and adds RFC3168 section 6.1.1.1. fallback for outgoing ECN connections. In other words, this work adds a retry with a non-ECN setup SYN packet, as suggested from the RFC on the first timeout: [...] A host that receives no reply to an ECN-setup SYN within the normal SYN retransmission timeout interval MAY resend the SYN and any subsequent SYN retransmissions with CWR and ECE cleared. [...] Schematic client-side view when assuming the server is in tcp_ecn=2 mode, that is, Linux default since 2009 via commit 255cac91c3c9 ("tcp: extend ECN sysctl to allow server-side only ECN"): 1) Normal ECN-capable path: SYN ECE CWR -----> <----- SYN ACK ECE ACK -----> 2) Path with broken middlebox, when client has fallback: SYN ECE CWR ----X crappy middlebox drops packet (timeout, rtx) SYN -----> <----- SYN ACK ACK -----> In case we would not have the fallback implemented, the middlebox drop point would basically end up as: SYN ECE CWR ----X crappy middlebox drops packet (timeout, rtx) SYN ECE CWR ----X crappy middlebox drops packet (timeout, rtx) SYN ECE CWR ----X crappy middlebox drops packet (timeout, rtx) In any case, it's rather a smaller percentage of sites where there would occur such additional setup latency: it was found in end of 2014 that ~56% of IPv4 and 65% of IPv6 servers of Alexa 1 million list would negotiate ECN (aka tcp_ecn=2 default), 0.42% of these webservers will fail to connect when trying to negotiate with ECN (tcp_ecn=1) due to timeouts, which the fallback would mitigate with a slight latency trade-off. Recent related paper on this topic: Brian Trammell, Mirja Kühlewind, Damiano Boppart, Iain Learmonth, Gorry Fairhurst, and Richard Scheffenegger: "Enabling Internet-Wide Deployment of Explicit Congestion Notification." Proc. PAM 2015, New York. http://ecn.ethz.ch/ecn-pam15.pdf Thus, when net.ipv4.tcp_ecn=1 is being set, the patch will perform RFC3168, section 6.1.1.1. fallback on timeout. For users explicitly not wanting this which can be in DC use case, we add a net.ipv4.tcp_ecn_fallback knob that allows for disabling the fallback. tp->ecn_flags are not being cleared in tcp_ecn_clear_syn() on output, but rather we let tcp_ecn_rcv_synack() take that over on input path in case a SYN ACK ECE was delayed. Thus a spurious SYN retransmission will not prevent ECN being negotiated eventually in that case. Reference: https://www.ietf.org/proceedings/92/slides/slides-92-iccrg-1.pdf Reference: https://www.ietf.org/proceedings/89/slides/slides-89-tsvarea-1.pdf Signed-off-by: Daniel Borkmann Signed-off-by: Florian Westphal Signed-off-by: Mirja Kühlewind Signed-off-by: Brian Trammell Cc: Eric Dumazet Cc: Dave That Acked-by: Eric Dumazet Signed-off-by: David S. Miller

ipv4: coding style: comparison for equality with NULL

2015-04-03T16:11:15+00:00

The ipv4 code uses a mixture of coding styles. In some instances check for NULL pointer is done as x == NULL and sometimes as !x. !x is preferred according to checkpatch and this patch makes the code consistent by adopting the latter form. No changes detected by objdiff. Signed-off-by: Ian Morris Signed-off-by: David S. Miller

ipv4: Create probe timer for tcp PMTU as per RFC4821

2015-03-06T19:57:42+00:00

As per RFC4821 7.3. Selecting Probe Size, a probe timer should be armed once probing has converged. Once this timer expired, probing again to take advantage of any path PMTU change. The recommended probing interval is 10 minutes per RFC1981. Probing interval could be sysctled by sysctl_tcp_probe_interval. Eric Dumazet suggested to implement pseudo timer based on 32bits jiffies tcp_time_stamp instead of using classic timer for such rare event. Signed-off-by: Fan Du Signed-off-by: David S. Miller

ipv4: Use binary search to choose tcp PMTU probe_size

2015-03-06T19:57:41+00:00

Current probe_size is chosen by doubling mss_cache, the probing process will end shortly with a sub-optimal mss size, and the link mtu will not be taken full advantage of, in return, this will make user to tweak tcp_base_mss with care. Use binary search to choose probe_size in a fine granularity manner, an optimal mss will be found to boost performance as its maxmium. In addition, introduce a sysctl_tcp_probe_threshold to control when probing will stop in respect to the width of search range. Test env: Docker instance with vxlan encapuslation(82599EB) iperf -c 10.0.0.24 -t 60 before this patch: 1.26 Gbits/sec After this patch: increase 26% 1.59 Gbits/sec Signed-off-by: Fan Du Acked-by: John Heffner Signed-off-by: David S. Miller

ipv4: Namespecify TCP PMTU mechanism

2015-02-10T02:45:00+00:00

Packetization Layer Path MTU Discovery works separately beside Path MTU Discovery at IP level, different net namespace has various requirements on which one to chose, e.g., a virutalized container instance would require TCP PMTU to probe an usable effective mtu for underlying tunnel, while the host would employ classical ICMP based PMTU to function. Hence making TCP PMTU mechanism per net namespace to decouple two functionality. Furthermore the probe base MSS should also be configured separately for each namespace. Signed-off-by: Fan Du Signed-off-by: David S. Miller

tcp: helpers to mitigate ACK loops by rate-limiting out-of-window dupacks

2015-02-08T09:03:12+00:00

Helpers for mitigating ACK loops by rate-limiting dupacks sent in response to incoming out-of-window packets. This patch includes: - rate-limiting logic - sysctl to control how often we allow dupacks to out-of-window packets - SNMP counter for cases where we rate-limited our dupack sending The rate-limiting logic in this patch decides to not send dupacks in response to out-of-window segments if (a) they are SYNs or pure ACKs and (b) the remote endpoint is sending them faster than the configured rate limit. We rate-limit our responses rather than blocking them entirely or resetting the connection, because legitimate connections can rely on dupacks in response to some out-of-window segments. For example, zero window probes are typically sent with a sequence number that is below the current window, and ZWPs thus expect to thus elicit a dupack in response. We allow dupacks in response to TCP segments with data, because these may be spurious retransmissions for which the remote endpoint wants to receive DSACKs. This is safe because segments with data can't realistically be part of ACK loops, which by their nature consist of each side sending pure/data-less ACKs to each other. The dupack interval is controlled by a new sysctl knob, tcp_invalid_ratelimit, given in milliseconds, in case an administrator needs to dial this upward in the face of a high-rate DoS attack. The name and units are chosen to be analogous to the existing analogous knob for ICMP, icmp_ratelimit. The default value for tcp_invalid_ratelimit is 500ms, which allows at most one such dupack per 500ms. This is chosen to be 2x faster than the 1-second minimum RTO interval allowed by RFC 6298 (section 2, rule 2.4). We allow the extra 2x factor because network delay variations can cause packets sent at 1 second intervals to be compressed and arrive much closer. Reported-by: Avery Fay Signed-off-by: Neal Cardwell Signed-off-by: Yuchung Cheng Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller