resource exhaustion attacks.
For network link optimization TCP can adjust its MSS and thus
packet size according to the observed path MTU. This is done
dynamically based on feedback from the remote host and network
components along the packet path. This information can be
abused to pretend an extremely low path MTU.
The resource exhaustion works in two ways:
o during tcp connection setup the advertized local MSS is
exchanged between the endpoints. The remote endpoint can
set this arbitrarily low (except for a minimum MTU of 64
octets enforced in the BSD code). When the local host is
sending data it is forced to send many small IP packets
instead of a large one.
For example instead of the normal TCP payload size of 1448
it forces TCP payload size of 12 (MTU 64) and thus we have
a 120 times increase in workload and packets. On fast links
this quickly saturates the local CPU and may also hit pps
processing limites of network components along the path.
This type of attack is particularly effective for servers
where the attacker can download large files (WWW and FTP).
We mitigate it by enforcing a minimum MTU settable by sysctl
net.inet.tcp.minmss defaulting to 256 octets.
o the local host is reveiving data on a TCP connection from
the remote host. The local host has no control over the
packet size the remote host is sending. The remote host
may chose to do what is described in the first attack and
send the data in packets with an TCP payload of at least
one byte. For each packet the tcp_input() function will
be entered, the packet is processed and a sowakeup() is
signalled to the connected process.
For example an attack with 2 Mbit/s gives 4716 packets per
second and the same amount of sowakeup()s to the process
(and context switches).
This type of attack is particularly effective for servers
where the attacker can upload large amounts of data.
Normally this is the case with WWW server where large POSTs
can be made.
We mitigate this by calculating the average MSS payload per
second. If it goes below 'net.inet.tcp.minmss' and the pps
rate is above 'net.inet.tcp.minmssoverload' defaulting to
1000 this particular TCP connection is resetted and dropped.
MITRE CVE: CAN-2004-0002
Reviewed by: sam (mentor)
MFC after: 1 day
rfc3042 Limited retransmit
rfc3390 Increasing TCP's initial congestion Window
inflight TCP inflight bandwidth limiting
All my production server have it enabled and there have been no
issues. I am confident about having them on by default and it gives
us better overall TCP performance.
Reviewed by: sam (mentor)
wait, rather than the socket label. This avoids reaching up to
the socket layer during connection close, which requires locking
changes. To do this, introduce MAC Framework entry point
mac_create_mbuf_from_inpcb(), which is called from tcp_twrespond()
instead of calling mac_create_mbuf_from_socket() or
mac_create_mbuf_netlayer(). Introduce MAC Policy entry point
mpo_create_mbuf_from_inpcb(), and implementations for various
policies, which generally just copy label data from the inpcb to
the mbuf. Assert the inpcb lock in the entry point since we
require consistency for the inpcb label reference.
Obtained from: TrustedBSD Project
Sponsored by: DARPA, Network Associates Laboratories
zeroed. Doing a bzero on the entire struct route is not more
expensive than assigning NULL to ro.ro_rt and bzero of ro.ro_dst.
Reviewed by: sam (mentor)
Approved by: re (scottl)
the routing table. Move all usage and references in the tcp stack
from the routing table metrics to the tcp hostcache.
It caches measured parameters of past tcp sessions to provide better
initial start values for following connections from or to the same
source or destination. Depending on the network parameters to/from
the remote host this can lead to significant speedups for new tcp
connections after the first one because they inherit and shortcut
the learning curve.
tcp_hostcache is designed for multiple concurrent access in SMP
environments with high contention and is hash indexed by remote
ip address.
It removes significant locking requirements from the tcp stack with
regard to the routing table.
Reviewed by: sam (mentor), bms
Reviewed by: -net, -current, core@kame.net (IPv6 parts)
Approved by: re (scottl)
o add assertions in tcp_respond to validate inpcb locking assumptions
o use local variable instead of chasing pointers in tcp_respond
Supported by: FreeBSD Foundation
previously only considered the send sequence space. Unfortunately,
some OSes (windows) still use a random positive increments scheme for
their syn-ack ISNs, so I must consider receive sequence space as well.
The value of 250000 bytes / second for Microsoft's ISN rate of increase
was determined by testing with an XP machine.
we will generate for a given ip/port tuple has advanced far enough
for the time_wait socket in question to be safely recycled.
- Have in_pcblookup_local use tcp_twrecycleable to determine if
time_Wait sockets which are hogging local ports can be safely
freed.
This change preserves proper TIME_WAIT behavior under normal
circumstances while allowing for safe and fast recycling whenever
ephemeral port space is scarce.
that at most 20% of sockets can be in time_wait at one time, ensuring
that time_wait sockets do not starve real connections from inpcb
structures.
No implementation change is needed, jlemon already implemented a nice
LRU-ish algorithm for tcp_tw structure recycling.
This should reduce the need for sysadmins to lower the default msl on
busy servers.
mac_reflect_mbuf_icmp()
mac_reflect_mbuf_tcp()
These entry points permit MAC policies to do "update in place"
changes to the labels on ICMP and TCP mbuf headers when an ICMP or
TCP response is generated to a packet outside of the context of
an existing socket. For example, in respond to a ping or a RST
packet to a SYN on a closed port.
Obtained from: TrustedBSD Project
Sponsored by: DARPA, Network Associates Laboratories
sure that the MAC label on TCP responses during TIMEWAIT is
properly set from either the socket (if available), or the mbuf
that it's responding to.
Unfortunately, this is made somewhat difficult by the TCP code,
as tcp_twstart() calls tcp_twrespond() after discarding the socket
but without a reference to the mbuf that causes the "response".
Passing both the socket and the mbuf works arounds this--eventually
it might be good to make sure the mbuf always gets passed in in
"response" scenarios but working through this provided to
complicate things too much.
Approved by: re (scottl)
Reviewed by: hsu
Obtained from: TrustedBSD Project
Sponsored by: DARPA, Network Associates Laboratories
state. Those changed attempted to work around the changed invariant
that inp->in_socket was sometimes now NULL, but the logic wasn't
quite right, meaning that inp->in_socket would be dereferenced by
cr_canseesocket() if security.bsd.see_other_uids, jail, or MAC
were in use. Attempt to clarify and correct the logic.
Note: the work-around originally introduced with the reduced TCP
wait state handling to use cr_cansee() instead of cr_canseesocket()
in this case isn't really right, although it "Does the right thing"
for most of the cases in the base system. We'll need to address
this at some point in the future.
Pointed out by: dcs
Obtained from: TrustedBSD Project
Sponsored by: DARPA, Network Associates Laboratories
tcpcb is NULL, but also its connected inpcb, since we now allow
elements of a TCP connection to hang around after other state, such
as the socket, has been recycled.
Tested by: dcs
Obtained from: TrustedBSD Project
Sponsored by: DARPA, Network Associates Laboratories
control block. Allow the socket and tcpcb structures to be freed
earlier than inpcb. Update code to understand an inp w/o a socket.
Reviewed by: hsu, silby, jayanth
Sponsored by: DARPA, NAI Labs
routine does not require a tcpcb to operate. Since we no longer keep
template mbufs around, move pseudo checksum out of this routine, and
merge it with the length update.
Sponsored by: DARPA, NAI Labs
Remove the never completed _IP_VHL version, it has not caught on
anywhere and it would make us incompatible with other BSD netstacks
to retain this version.
Add a CTASSERT protecting sizeof(struct ip) == 20.
Don't let the size of struct ipq depend on the IPDIVERT option.
This is a functional no-op commit.
Approved by: re
configuration stuff as well as conditional code in the IPv4 and IPv6
areas. Everything is conditional on FAST_IPSEC which is mutually
exclusive with IPSEC (KAME IPsec implmentation).
As noted previously, don't use FAST_IPSEC with INET6 at the moment.
Reviewed by: KAME, rwatson
Approved by: silence
Supported by: Vernier Networks
o instead of a list of mbufs use a list of m_tag structures a la openbsd
o for netgraph et. al. extend the stock openbsd m_tag to include a 32-bit
ABI/module number cookie
o for openbsd compatibility define a well-known cookie MTAG_ABI_COMPAT and
use this in defining openbsd-compatible m_tag_find and m_tag_get routines
o rewrite KAME use of aux mbufs in terms of packet tags
o eliminate the most heavily used aux mbufs by adding an additional struct
inpcb parameter to ip_output and ip6_output to allow the IPsec code to
locate the security policy to apply to outbound packets
o bump __FreeBSD_version so code can be conditionalized
o fixup ipfilter's call to ip_output based on __FreeBSD_version
Reviewed by: julian, luigi (silent), -arch, -net, darren
Approved by: julian, silence from everyone else
Obtained from: openbsd (mostly)
MFC after: 1 month
not meant to duplicate) TCP/Vegas. Add four sysctls and default the
implementation to 'off'.
net.inet.tcp.inflight_enable enable algorithm (defaults to 0=off)
net.inet.tcp.inflight_debug debugging (defaults to 1=on)
net.inet.tcp.inflight_min minimum window limit
net.inet.tcp.inflight_max maximum window limit
MFC after: 1 week
pointer and incoming mbuf pointer will be non-NULL in tcp_respond().
This is relied on by the MAC code for correctness, as well as
existing code.
Obtained from: TrustedBSD PRoject
Sponsored by: DARPA, NAI Labs
kernel access control.
Instrument the TCP socket code for packet generation and delivery:
label outgoing mbufs with the label of the socket, and check socket and
mbuf labels before permitting delivery to a socket. Assign labels
to newly accepted connections when the syncache/cookie code has done
its business. Also set peer labels as convenient. Currently,
MAC policies cannot influence the PCB matching algorithm, so cannot
implement polyinstantiation. Note that there is at least one case
where a PCB is not available due to the TCP packet not being associated
with any socket, so we don't label in that case, but need to handle
it in a special manner.
Obtained from: TrustedBSD Project
Sponsored by: DARPA, NAI Labs
SYSCTL_OUT() from blocking while locks are held. This should
only be done when it would be inconvenient to make a temporary copy of
the data and defer calling SYSCTL_OUT() until after the locks are
released.
net.inet.tcp.rexmit_min (default 3 ticks equiv)
This sysctl is the retransmit timer RTO minimum,
specified in milliseconds. This value is
designed for algorithmic stability only.
net.inet.tcp.rexmit_slop (default 200ms)
This sysctl is the retransmit timer RTO slop
which is added to every retransmit timeout and
is designed to handle protocol stack overheads
and delayed ack issues.
Note that the *original* code applied a 1-second
RTO minimum but never applied real slop to the RTO
calculation, so any RTO calculation over one second
would have no slop and thus not account for
protocol stack overheads (TCP timestamps are not
a measure of protocol turnaround!). Essentially,
the original code made the RTO calculation almost
completely irrelevant.
Please note that the 200ms slop is debateable.
This commit is not meant to be a line in the sand,
and if the community winds up deciding that increasing
it is the correct solution then it's easy to do.
Note that larger values will destroy performance
on lossy networks while smaller values may result in
a greater number of unnecessary retransmits.
so that, if we recieve a ICMP "time to live exceeded in transit",
(type 11, code 0) for a TCP connection on SYN-SENT state, close
the connection.
MFC after: 2 weeks
indication of whether this happenned so the calling function
knows whether or not to unlock the pcb.
Submitted by: Jennifer Yang (yangjihui@yahoo.com)
Bug reported by: Sid Carter (sidcarter@symonds.net)
o Add a mutex (sb_mtx) to struct sockbuf. This protects the data in a
socket buffer. The mutex in the receive buffer also protects the data
in struct socket.
o Determine the lock strategy for each members in struct socket.
o Lock down the following members:
- so_count
- so_options
- so_linger
- so_state
o Remove *_locked() socket APIs. Make the following socket APIs
touching the members above now require a locked socket:
- sodisconnect()
- soisconnected()
- soisconnecting()
- soisdisconnected()
- soisdisconnecting()
- sofree()
- soref()
- sorele()
- sorwakeup()
- sotryfree()
- sowakeup()
- sowwakeup()
Reviewed by: alfred
general cleanup of the API. The entire API now consists of two functions
similar to the pre-KSE API. The suser() function takes a thread pointer
as its only argument. The td_ucred member of this thread must be valid
so the only valid thread pointers are curthread and a few kernel threads
such as thread0. The suser_cred() function takes a pointer to a struct
ucred as its first argument and an integer flag as its second argument.
The flag is currently only used for the PRISON_ROOT flag.
Discussed on: smp@
Move the network code from using cr_cansee() to check whether a
socket is visible to a requesting credential to using a new
function, cr_canseesocket(), which accepts a subject credential
and object socket. Implement cr_canseesocket() so that it does a
prison check, a uid check, and add a comment where shortly a MAC
hook will go. This will allow MAC policies to seperately
instrument the visibility of sockets from the visibility of
processes.
Obtained from: TrustedBSD Project
Sponsored by: DARPA, NAI Labs
