The current TSO limitation feature only takes the total number of
bytes in an mbuf chain into account and does not limit by the number
of mbufs in a chain. Some kinds of hardware is limited by two
factors. One is the fragment length and the second is the fragment
count. Both of these limits need to be taken into account when doing
TSO. Else some kinds of hardware might have to drop completely valid
mbuf chains because they cannot loaded into the given hardware's DMA
engine. The new way of doing TSO limitation has been made backwards
compatible as input from other FreeBSD developers and will use
defaults for values not set.
Reviewed by: adrian, rmacklem
Sponsored by: Mellanox Technologies
MFC after: 1 week
towards blind SYN/RST spoofed attack.
Originally our stack used in-window checks for incoming SYN/RST
as proposed by RFC793. Later, circa 2003 the RST attack was
mitigated using the technique described in P. Watson
"Slipping in the window" paper [1].
After that, the checks were only relaxed for the sake of
compatibility with some buggy TCP stacks. First, r192912
introduced the vulnerability, just fixed by aforementioned SA.
Second, r167310 had slightly relaxed the default RST checks,
instead of utilizing net.inet.tcp.insecure_rst sysctl.
In 2010 a new technique for mitigation of these attacks was
proposed in RFC5961 [2]. The idea is to send a "challenge ACK"
packet to the peer, to verify that packet arrived isn't spoofed.
If peer receives challenge ACK it should regenerate its RST or
SYN with correct sequence number. This should not only protect
against attacks, but also improve communication with broken
stacks, so authors of reverted r167310 and r192912 won't be
disappointed.
[1] http://bandwidthco.com/whitepapers/netforensics/tcpip/TCP Reset Attacks.pdf
[2] http://www.rfc-editor.org/rfc/rfc5961.txt
Changes made:
o Revert r167310.
o Implement "challenge ACK" protection as specificed in RFC5961
against RST attack. On by default.
- Carefully preserve r138098, which handles empty window edge
case, not described by the RFC.
- Update net.inet.tcp.insecure_rst description.
o Implement "challenge ACK" protection as specificed in RFC5961
against SYN attack. On by default.
- Provide net.inet.tcp.insecure_syn sysctl, to turn off
RFC5961 protection.
The changes were tested at Netflix. The tested box didn't show
any anomalies compared to control box, except slightly increased
number of TCP connection in LAST_ACK state.
Reviewed by: rrs
Sponsored by: Netflix
Sponsored by: Nginx, Inc.
packets targeting a listening socket. Permit to reduce TCP input
processing starvation in context of high SYN load (e.g. short-lived TCP
connections or SYN flood).
Submitted by: Julien Charbon <jcharbon@verisign.com>
Reviewed by: adrian, hiren, jhb, Mike Bentkofsky
mixing on stack memory and UMA memory in one linked list.
Thus, rewrite TCP reassembly code in terms of memory usage. The
algorithm remains unchanged.
We actually do not need extra memory to build a reassembly queue.
Arriving mbufs are always packet header mbufs. So we got the length
of data as pkthdr.len. We got m_nextpkt for linkage. And we need
only one pointer to point at the tcphdr, use PH_loc for that.
In tcpcb the t_segq fields becomes mbuf pointer. The t_segqlen
field now counts not packets, but bytes in the queue. This gives
us more precision when comparing to socket buffer limits.
Sponsored by: Netflix
Sponsored by: Nginx, Inc.
By definition, the very first FIN is not a duplicate. Process it normally
and don't feed it to congestion control as though it were a dupe. Don't
prevent CC from seeing later dupe acks while in a half close state.
- The remote host sends a FIN
- in an ACK for a sequence number for which an ACK has already
been received
- There is still unacked data on route to the remote host
- The packet does not contain a window update
The packet may be dropped without processing the FIN flag.
PR: kern/99188
Submitted by: Staffan Ulfberg <staffan@ulfberg.se>
Discussed with: andre
MFC after: never
In its stead use the Solaris / illumos approach of emulating '-' (dash)
in probe names with '__' (two consecutive underscores).
Reviewed by: markj
MFC after: 3 weeks
option, unbreak the lock tracing release semantic by embedding
calls to LOCKSTAT_PROFILE_RELEASE_LOCK() direclty in the inlined
version of the releasing functions for mutex, rwlock and sxlock.
Failing to do so skips the lockstat_probe_func invokation for
unlocking.
- As part of the LOCKSTAT support is inlined in mutex operation, for
kernel compiled without lock debugging options, potentially every
consumer must be compiled including opt_kdtrace.h.
Fix this by moving KDTRACE_HOOKS into opt_global.h and remove the
dependency by opt_kdtrace.h for all files, as now only KDTRACE_FRAMES
is linked there and it is only used as a compile-time stub [0].
[0] immediately shows some new bug as DTRACE-derived support for debug
in sfxge is broken and it was never really tested. As it was not
including correctly opt_kdtrace.h before it was never enabled so it
was kept broken for a while. Fix this by using a protection stub,
leaving sfxge driver authors the responsibility for fixing it
appropriately [1].
Sponsored by: EMC / Isilon storage division
Discussed with: rstone
[0] Reported by: rstone
[1] Discussed with: philip
to this event, adding if_var.h to files that do need it. Also, include
all includes that now are included due to implicit pollution via if_var.h
Sponsored by: Netflix
Sponsored by: Nginx, Inc.
segments thinking it received only one segment. This causes it to enable
the delay the ACK for 100ms to wait for another segment which may never
come because all the data was received already.
Doing delayed ACK for LRO segments is bogus for two reasons: a) it pushes
us further away from acking every other packet; b) it introduces additional
delay in responding to the sender. The latter is especially bad because it
is in the nature of LRO to aggregated all segments of a burst with no more
coming until an ACK is sent back.
Change the delayed ACK logic to detect LRO segments by being larger than
the MSS for this connection and issuing an immediate ACK for them to keep
the ACK clock ticking without interruption.
Reported by: julian, cperciva
Tested by: cperciva
Reviewed by: lstewart
MFC after: 3 days
sbdrop_locked() to cut acked mbufs from the socket buffer. Free this
chain a batch manner after the socket buffer lock is dropped.
This measurably reduces contention on socket buffer.
Sponsored by: Netflix
Sponsored by: Nginx, Inc.
Approved by: re (marius)
dynamic translation so that their arguments match the definitions for
these providers in Solaris and illumos. Thus, existing scripts for these
providers should work unmodified on FreeBSD.
Tested by: gnn, hiren
MFC after: 1 month
structure is used, but they already have equal fields in the struct
newipsecstat, that was introduced with FAST_IPSEC and then was merged
together with old ipsecstat structure.
This fixes kernel stack overflow on some architectures after migration
ipsecstat to PCPU counters.
Reported by: Taku YAMAMOTO, Maciej Milewski
increased the pointer, not the memory it points to.
In collaboration with: kib
Reported & tested by: Ian FREISLICH <ianf clue.co.za>
Sponsored by: Nginx, Inc.
limited in the amount of data they can handle at once.
Drivers can set ifp->if_hw_tsomax before calling ether_ifattach() to
change the limit.
The lowest allowable size is IP_MAXPACKET / 8 (8192 bytes) as anything
less wouldn't be very useful anymore. The upper limit is still at
IP_MAXPACKET (65536 bytes). Raising it requires further auditing of
the IPv4/v6 code path's as the length field in the IP header would
overflow leading to confusion in firewalls and others packet handler on
the real size of the packet.
The placement into "struct ifnet" is a bit hackish but the best place
that was found. When the stack/driver boundary is updated it should
be handled in a better way.
Submitted by: cperciva (earlier version)
Reviewed by: cperciva
Tested by: cperciva
MFC after: 1 week (using spare struct members to preserve ABI)
duplicate ACK make sure we actually have new data to send.
This prevents us from sending unneccessary pure ACKs.
Reported by: Matt Miller <matt@matthewjmiller.net>
Tested by: Matt Miller <matt@matthewjmiller.net>
MFC after: 2 weeks
connections in the accept queue and contiguous new incoming SYNs.
Compared to the original submitters patch I've moved the test
next to the SYN handling to have it together in a logical unit
and reworded the comment explaining the issue.
Submitted by: Matt Miller <matt@matthewjmiller.net>
Submitted by: Juan Mojica <jmojica@gmail.com>
Reviewed by: Matt Miller (changes)
Tested by: pho
MFC after: 1 week
Convert 'struct ipstat' and 'struct tcpstat' to counter(9).
This speeds up IP forwarding at extreme packet rates, and
makes accounting more precise.
Sponsored by: Nginx, Inc.
For TIMEWAIT handling tcp_input may have to jump back for an additional
pass through pcblookup. Prior to this change the fwd_tag had been
discarded after the first lookup, so a new connection attempt delivered
locally via 'ipfw fwd' would fail to find a match.
As of r248886 the tag will be detached and freed when passed to the
socket buffer.
logic (refer to [1] for associated discussion). snd_cwnd and snd_wnd are
unsigned long and on 64 bit hosts, min() will truncate them to 32 bits and could
therefore potentially corrupt the result (although under normal operation,
neither variable should legitmately exceed 32 bits).
[1] http://lists.freebsd.org/pipermail/freebsd-net/2013-January/034297.html
Submitted by: jhb
MFC after: 1 week
but later after processing and freeing the tag, we need to jump back again
to the findpcb label. Since the fwd_tag pointer wasn't NULL we tried to
process and free the tag for second time.
Reported & tested by: Pawel Tyll <ptyll nitronet.pl>
MFC after: 3 days
Instead, add protocol specific mbuf flags M_IP_NEXTHOP and
M_IP6_NEXTHOP. Use them to indicate that the mbuf's chain
contains the PACKET_TAG_IPFORWARD tag. And do a tag lookup
only when this flag is set.
Suggested by: andre
draft-ietf-tcpm-initcwnd-05. It explains why the increased initial
window improves the overall performance of many web services without
risking congestion collapse.
As long as it remains a draft it is placed under a sysctl marking it
as experimental:
net.inet.tcp.experimental.initcwnd10 = 1
When it becomes an official RFC soon the sysctl will be changed to
the RFC number and moved to net.inet.tcp.
This implementation differs from the RFC draft in that it is a bit
more conservative in the case of packet loss on SYN or SYN|ACK because
we haven't reduced the default RTO to 1 second yet. Also the restart
window isn't yet increased as allowed. Both will be adjusted with
upcoming changes.
Is is enabled by default. In Linux it is enabled since kernel 3.0.
MFC after: 2 weeks
especially in the presence of bi-directional data transfers.
snd_wl1 tracks the right edge, including data in the reassembly
queue, of valid incoming data. This makes it like rcv_nxt plus
reassembly. It never goes backwards to prevent older, possibly
reordered segments from updating the window.
snd_wl2 tracks the left edge of sent data. This makes it a duplicate
of snd_una. However joining them right now is difficult due to
separate update dependencies in different places in the code flow.
snd_wnd tracks the current advertized send window by the peer. In
tcp_output() the effective window is calculated by subtracting the
already in-flight data, snd_nxt less snd_una, from it.
ACK's become the main clock of window updates and will always update
the window when the left edge of what we sent is advanced. The ACK
clock is the primary signaling mechanism in ongoing data transfers.
This works reliably even in the presence of reordering, reassembly
and retransmitted segments. The ACK clock is most important because
it determines how much data we are allowed to inject into the network.
Zero window updates get us out of persistence mode are crucial. Here
a segment that neither moves ACK nor SEQ but enlarges WND is accepted.
When the ACK clock is not active (that is we're not or no longer
sending any data) any segment that moves the extended right SEQ edge,
including out-of-order segments, updates the window. This gives us
updates especially during ping-pong transfers where the peer isn't
done consuming the already acknowledged data from the receive buffer
while responding with data.
The SSH protocol is a prime candidate to benefit from the improved
bi-directional window update logic as it has its own windowing
mechanism on top of TCP and is frequently sending back protocol ACK's.
Tcpdump provided by: darrenr
Tested by: darrenr
MFC after: 2 weeks
We've got more cluster sizes for quite some time now and the orginally
imposed limits and the previously codified thoughts on efficiency gains
are no longer true.
MFC after: 2 weeks
reduce the initial CWND to one segment. This reduction got lost
some time ago due to a change in initialization ordering.
Additionally in tcp_timer_rexmt() avoid entering fast recovery when
we're still in TCPS_SYN_SENT state.
MFC after: 2 weeks
on the related functionality in the runtime via the sysctl variable
net.pfil.forward. It is turned off by default.
Sponsored by: Yandex LLC
Discussed with: net@
MFC after: 2 weeks
before passing a packet to protocol input routines.
For several protocols this mean that now protocol needs to
do subtraction itself, and for another half this means that
we do not need to add header length back to the packet.
Make ip_stripoptions() to adjust ip_len, since now we enter
this function with a packet header whose ip_len does represent
length of entire packet, not payload only.
in network byte order. Any host byte order processing is
done in local variables and host byte order values are
never[1] written to a packet.
After this change a packet processed by the stack isn't
modified at all[2] except for TTL.
After this change a network stack hacker doesn't need to
scratch his head trying to figure out what is the byte order
at the given place in the stack.
[1] One exception still remains. The raw sockets convert host
byte order before pass a packet to an application. Probably
this would remain for ages for compatibility.
[2] The ip_input() still subtructs header len from ip->ip_len,
but this is planned to be fixed soon.
Reviewed by: luigi, Maxim Dounin <mdounin mdounin.ru>
Tested by: ray, Olivier Cochard-Labbe <olivier cochard.me>
