As data from socket is forwarded to the guest, sendmmsg() might send
fewer bytes than requested in three different ways:
- failing altogether with a negative error code -- ignore that,
we'll get an error on the UNIX domain socket later if there's
really an issue with it and reset the connection to the guest
- sending less than 'vlen' messages -- instead of assuming success
in that case and waiting for the guest to send a duplicate ACK
indicating missing data, update the sequence number according to
what was actually sent and spare some retransmissions
- somewhat unexpectedly to me, sending 'vlen' or less than 'vlen'
messages, returning up to 'vlen', with the last message being
partially sent, and no further indication of errors other than
the returned msg_len for the last partially sent message being
less than iov_len.
In this case, we would assume success and proceed as nothing
happened. However, qemu would fail to parse any further message,
having received a partial descriptor, and eventually close the
connection, logging:
serious error: oversized packet received,connection terminated.
as the length descriptor for the next message would be sourced
from the middle of the next successfully sent message, not from
its header.
Handle this by checking the msg_len returned for the last (even
partially) sent message, and force re-sending the missing bytes,
if any, with a blocking sendmsg() -- qemu must not receive
anything else than that anyway.
While at it, allow to send up to 64KiB for each message, the
previous 32KiB limit isn't actually required, and just switch to a
new message at each iteration on sending buffers, they are already
MSS-sized anyway, so the check in the loop isn't really needed.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
With a kernel older than 5.3 (no_snd_wnd set), ack_pending in
tcp_send_to_tap() might be true at the beginning of a new connection
initiated by a socket. This means we send the first SYN segment to the
tap together with ACK set, which is clearly invalid and triggers the
receiver to reply with an RST segment right away.
Set ack_pending to 0 whenever we're sending a SYN segment. In case of a
SYN, ACK segment sent by the caller, the caller passes the ACK flag
explicitly.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Socket-facing functions don't guarantee that all data is handled before
they return: stick to level-triggered mode for TCP sockets.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
...and while at it, fix an issue in the calculation of the last IOV
buffer size: if we can't receive enough data to fill up the window,
the last buffer can be filled completely.
Also streamline the code setting iovec lengths if cached values are
not matching.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
We won't necessarily have another choice to ACK in a timely fashion
if we skip ACKs from a number of states (including ESTABLISHED) when
there's enough window left. Check for ACKed bytes as soon as it makes
sense.
If the sending window is not reported by the kernel, ACK as soon as
we queue onto the socket, given that we're forced to use a rather
small window.
In FIN_WAIT_1_SOCK_FIN, we also have to account for the FIN flag sent
by the peer in the sequence.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Sending 64 frames in a batch looks quite bad when a duplicate ACK
comes right at the beginning of it. Lowering this to 32 doesn't
affect performance noticeably, with 16 the impact is more apparent.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Similar to UDP, but using a simple sendmsg() on iovec-style buffers
from tap instead, as we don't need to preserve message boundaries.
A quick test in PASTA mode, from namespace to init via tap:
# ip link set dev pasta0 mtu 16384
# iperf3 -c 192.168.1.222 -t 60
[...]
[ ID] Interval Transfer Bitrate
[ 5] 0.00-60.00 sec 80.4 GBytes 11.5 Gbits/sec receiver
# iperf3 -c 2a02:6d40:3cfc:3a01:2b20:4a6a:c25a:3056 -t 60
[...]
[ ID] Interval Transfer Bitrate
[ 5] 0.00-60.01 sec 39.9 GBytes 5.71 Gbits/sec receiver
# ip link set dev pasta0 mtu 65520
# iperf3 -c 192.168.1.222 -t 60
[...]
[ ID] Interval Transfer Bitrate
[ 5] 0.00-60.01 sec 88.7 GBytes 12.7 Gbits/sec receiver
# iperf3 -c 2a02:6d40:3cfc:3a01:2b20:4a6a:c25a:3056 -t 60
[...]
[ ID] Interval Transfer Bitrate
[ 5] 0.00-60.00 sec 79.5 GBytes 11.4 Gbits/sec receiver
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
There's no need to constantly query the socket for number of
acknowledged bytes if we're far from exhausting the sending window,
just do it if we're at least down to 90% of it.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Traffic with loopback source address will be forwarded to the direct
loopback connection in the namespace, and the tap interface is used
for the rest.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This isn't optional: TCP streams must carry a unique, hard-to-guess,
non-zero label for each direction. Linux, probably among others,
will otherwise refuse to associate packets in a given stream to the
same connection.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Allow to bind IPv4 and IPv6 ports to tap, namespace or init separately.
Port numbers of TCP ports that are bound in a namespace are also bound
for UDP for convenience (e.g. iperf3), and IPv4 ports are always bound
if the corresponding IPv6 port is bound (socket might not have the
IPV6_V6ONLY option set). This will also be configurable later.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
...not just for loopback addresses, with the address of the default
gateway. Otherwise, the guest might receive packets with source and
destination set to the same address.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This is actually reasonable in terms of memory consumption and
allows for better performance with local services.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
PASTA (Pack A Subtle Tap Abstraction) provides quasi-native host
connectivity to an otherwise disconnected, unprivileged network
and user namespace, similarly to slirp4netns. Given that the
implementation is largely overlapping with PASST, no separate binary
is built: 'pasta' (and 'passt4netns' for clarity) both link to
'passt', and the mode of operation is selected depending on how the
binary is invoked. Usage example:
$ unshare -rUn
# echo $$
1871759
$ ./pasta 1871759 # From another terminal
# udhcpc -i pasta0 2>/dev/null
# ping -c1 pasta.pizza
PING pasta.pizza (64.190.62.111) 56(84) bytes of data.
64 bytes from 64.190.62.111 (64.190.62.111): icmp_seq=1 ttl=255 time=34.6 ms
--- pasta.pizza ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 34.575/34.575/34.575/0.000 ms
# ping -c1 spaghetti.pizza
PING spaghetti.pizza(2606:4700:3034::6815:147a (2606:4700:3034::6815:147a)) 56 data bytes
64 bytes from 2606:4700:3034::6815:147a (2606:4700:3034::6815:147a): icmp_seq=1 ttl=255 time=29.0 ms
--- spaghetti.pizza ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 28.967/28.967/28.967/0.000 ms
This entails a major rework, especially with regard to the storage of
tracked connections and to the semantics of epoll(7) references.
Indexing TCP and UDP bindings merely by socket proved to be
inflexible and unsuitable to handle different connection flows: pasta
also provides Layer-2 to Layer-2 socket mapping between init and a
separate namespace for local connections, using a pair of splice()
system calls for TCP, and a recvmmsg()/sendmmsg() pair for UDP local
bindings. For instance, building on the previous example:
# ip link set dev lo up
# iperf3 -s
$ iperf3 -c ::1 -Z -w 32M -l 1024k -P2 | tail -n4
[SUM] 0.00-10.00 sec 52.3 GBytes 44.9 Gbits/sec 283 sender
[SUM] 0.00-10.43 sec 52.3 GBytes 43.1 Gbits/sec receiver
iperf Done.
epoll(7) references now include a generic part in order to
demultiplex data to the relevant protocol handler, using 24
bits for the socket number, and an opaque portion reserved for
usage by the single protocol handlers, in order to track sockets
back to corresponding connections and bindings.
A number of fixes pertaining to TCP state machine and congestion
window handling are also included here.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Before commit 8f7baad7f035 ("tcp: Add snd_wnd to TCP_INFO"), the
kernel didn't export tcpi_snd_wnd via TCP_INFO, which means we don't
know what's the window size of the receiver, socket-side.
To get TCP connections working in that case, ignore this value if
it's zero during handshake, and use the initial window value as
suggested by RFC 6928 (14 600 bytes, instead of 4 380 bytes), to
keep network performance usable.
To make the TCP dynamic responsive enough in this case, also check
the socket for available data whenever we get an ACK segment from
tap, instead of waiting until all the data from the tap is dequeued.
While at it, fix the window scaling value sent for SYN and SYN, ACK
segments: we want to increase the data pointer after writing the
option, not the value itself.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
During handshake, the initial SYN, ACK segment to the guest, send as
a response to the SYN segment, needs to report the unscaled value for
the window, given that the handshake hasn't completed yet.
While at it, fix the endianness for the window value in case TCP
parameters can't be queried via TCP_INFO and we need to use the
default value.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
and, given that the connection table is indexed by socket number,
we also need to increase MAX_CONNS now as the ICMP implementation
needs 2^17 sockets, that will be opened before TCP connections are
accepted.
This needs to be changed later: the connection table should be
indexed by a translated number -- we're wasting 2^17 table entries
otherwise. Move initialisation of TCP listening sockets as last
per-protocol initialisation, this will make it easier.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This is in preparation for scatter-gather IO on the UDP receive path:
save a getsockname() syscall by setting a flag if we get the numbering
of all bound sockets in a strict sequence (expected, in practice) and
repurpose the tap buffer to be also a socket receive buffer, passing
it down to protocol handlers.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
As we support UDP forwarding for packets that are sent to local
ports, we actually need some kind of connection tracking for UDP.
While at it, this commit introduces a number of vaguely related fixes
for issues observed while trying this out. In detail:
- implement an explicit, albeit minimalistic, connection tracking
for UDP, to allow usage of ephemeral ports by the guest and by
the host at the same time, by binding them dynamically as needed,
and to allow mapping address changes for packets with a loopback
address as destination
- set the guest MAC address whenever we receive a packet from tap
instead of waiting for an ARP request, and set it to broadcast on
start, otherwise DHCPv6 might not work if all DHCPv6 requests time
out before the guest starts talking IPv4
- split context IPv6 address into address we assign, global or site
address seen on tap, and link-local address seen on tap, and make
sure we use the addresses we've seen as destination (link-local
choice depends on source address). Similarly, for IPv4, split into
address we assign and address we observe, and use the address we
observe as destination
- introduce a clock_gettime() syscall right after epoll_wait() wakes
up, so that we can remove all the other ones and pass the current
timestamp to tap and socket handlers -- this is additionally needed
by UDP to time out bindings to ephemeral ports and mappings between
loopback address and a local address
- rename sock_l4_add() to sock_l4(), no semantic changes intended
- include <arpa/inet.h> in passt.c before kernel headers so that we
can use <netinet/in.h> macros to check IPv6 address types, and
remove a duplicate <linux/ip.h> inclusion
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Seen with iperf3 server on tap side: connection state is SOCK_SYN_SENT,
we haven't got an ACK from the tap yet (that's why we're not in
ESTABLISHED), but a data packet comes. Don't read this data until we
reach the ESTABLISHED state, by keeping EPOLLIN disabled until that
point.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Avoid a bunch of syscalls on forwarding paths by:
- storing minimum and maximum file descriptor numbers for each
protocol, fall back to SO_PROTOCOL query only on overlaps
- allocating a larger receive buffer -- this can result in more
coalesced packets than sendmmsg() can take (UIO_MAXIOV, i.e. 1024),
so make sure we don't exceed that within a single call to protocol
tap handlers
- nesting the handling loop in tap_handler() in the receive loop,
so that we have better chances of filling our receive buffer in
fewer calls
- skipping the recvfrom() in the UDP handler on EPOLLERR -- there's
nothing to be done in that case
and while at it:
- restore the 20ms timer interval for periodic (TCP) events, I
accidentally changed that to 100ms in an earlier commit
- attempt using SO_ZEROCOPY for UDP -- if it's not available,
sendmmsg() will succeed anyway
- fix the handling of the status code from sendmmsg(), if it fails,
we'll try to discard the first message, hence return 1 from the
UDP handler
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This is symmetric with tap operation and addressing model, and
allows again to reach the guest behind the tap interface by
contacting the local address.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Receive packets in batches from AF_UNIX, check if they can be sent
with a single syscall, and batch them up with sendmmsg() in case.
A bit rudimentary, currently only implemented for UDP, but it seems
to work.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
We don't need to keep small data as static variables, move the only
small variable we have so far to the new struct.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Replace the dummy, full array scan implementation, by a hash table
based on SipHash, with chained hashing for collisions.
This table is also statically allocated, and it's simply an array
of socket numbers. Connection entries are chained by pointers in
the connection entry itself, which now also contains socket number
and hash bucket index to keep removal reasonably fast.
New entries are inserted at the head of the chain, that is, the most
recently inserted entry is directly mapped from the bucket.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
We might receive out-of-order ACK packets from the tap device, just
like any other packet.
I guess I've been overcautious and regarded it as a condition we
can't recover from, but all that happens is that we have already seen
a higher ACK sequence number, which means that data has been already
received and discarded from the buffer. We have to ignore the lower
sequence number we receive later, though, because that would force
the buffer bookkeeping into throwing away more data than expected.
Drop the ACK sequence assignment from tcp_tap_handler(), which was
redundant, and let tcp_sock_consume() take exclusive care of that.
Now that tcp_sock_consume() can never fail, make it a void, and
drop checks from callers.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Implement siphash routines for initial TCP sequence numbers (12 bytes
input for IPv4, 36 bytes input for IPv6), and while at it, also
functions we'll use later on for hash table indices and TCP timestamp
offsets (with 8, 20, 32 bytes of input).
Use these to set the initial sequence number, according to RFC 6528,
for connections originating either from the tap device or from
sockets.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
A bunch of fixes not worth single commits at this stage, notably:
- make buffer, length parameter ordering consistent in ARP, DHCP,
NDP handlers
- strict checking of buffer, message and option length in DHCP
handler (a malicious client could have easily crashed it)
- set up forwarding for IPv4 and IPv6, and masquerading with nft for
IPv4, from demo script
- get rid of separate slow and fast timers, we don't save any
overhead that way
- stricter checking of buffer lengths as passed to tap handlers
- proper dequeuing from qemu socket back-end: I accidentally trashed
messages that were bundled up together in a single tap read
operation -- the length header tells us what's the size of the next
frame, but there's no apparent limit to the number of messages we
get with one single receive
- rework some bits of the TCP state machine, now passive and active
connection closes appear to be robust -- introduce a new
FIN_WAIT_1_SOCK_FIN state indicating a FIN_WAIT_1 with a FIN flag
from socket
- streamline TCP option parsing routine
- track TCP state changes to stderr (this is temporary, proper
debugging and syslogging support pending)
- observe that multiplying a number by four might very well change
its value, and this happens to be the case for the data offset
from the TCP header as we check if it's the same as the total
length to find out if it's a duplicated ACK segment
- recent estimates suggest that the duration of a millisecond is
closer to a million nanoseconds than a thousand of them, this
trend is now reflected into the timespec_diff_ms() convenience
routine
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This is a reimplementation, partially building on the earlier draft,
that uses L4 sockets (SOCK_DGRAM, SOCK_STREAM) instead of SOCK_RAW,
providing L4-L2 translation functionality without requiring any
security capability.
Conceptually, this follows the design presented at:
https://gitlab.com/abologna/kubevirt-and-kvm/-/blob/master/Networking.md
The most significant novelty here comes from TCP and UDP translation
layers. In particular, the TCP state and translation logic follows
the intent of being minimalistic, without reimplementing a full TCP
stack in either direction, and synchronising as much as possible the
TCP dynamic and flows between guest and host kernel.
Another important introduction concerns addressing, port translation
and forwarding. The Layer 4 implementations now attempt to bind on
all unbound ports, in order to forward connections in a transparent
way.
While at it:
- the qemu 'tap' back-end can't be used as-is by qrap anymore,
because of explicit checks now introduced in qemu to ensure that
the corresponding file descriptor is actually a tap device. For
this reason, qrap now operates on a 'socket' back-end type,
accounting for and building the additional header reporting
frame length
- provide a demo script that sets up namespaces, addresses and
routes, and starts the daemon. A virtual machine started in the
network namespace, wrapped by qrap, will now directly interface
with passt and communicate using Layer 4 sockets provided by the
host kernel.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
