inet: add IP_BIND_ADDRESS_NO_PORT to overcome bind(0) limitations
When an application needs to force a source IP on an active TCP socket
it has to use bind(IP, port=x).
As most applications do not want to deal with already used ports, x is
often set to 0, meaning the kernel is in charge to find an available
port.
But kernel does not know yet if this socket is going to be a listener or
be connected.
It has very limited choices (no full knowledge of final 4-tuple for a
connect())
With limited ephemeral port range (about 32K ports), it is very easy to
fill the space.
This patch adds a new SOL_IP socket option, asking kernel to ignore
the 0 port provided by application in bind(IP, port=0) and only
remember the given IP address.
The port will be automatically chosen at connect() time, in a way
that allows sharing a source port as long as the 4-tuples are unique.
This new feature is available for both IPv4 and IPv6 (Thanks Neal)
Tested:
Wrote a test program and checked its behavior on IPv4 and IPv6.
strace(1) shows sequences of bind(IP=127.0.0.2, port=0) followed by
connect().
Also getsockname() show that the port is still 0 right after bind()
but properly allocated after connect().
socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 5
setsockopt(5, SOL_IP, IP_BIND_ADDRESS_NO_PORT, [1], 4) = 0
bind(5, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("127.0.0.2")}, 16) = 0
getsockname(5, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("127.0.0.2")}, [16]) = 0
connect(5, {sa_family=AF_INET, sin_port=htons(53174), sin_addr=inet_addr("127.0.0.3")}, 16) = 0
getsockname(5, {sa_family=AF_INET, sin_port=htons(38050), sin_addr=inet_addr("127.0.0.2")}, [16]) = 0
IPv6 test :
socket(PF_INET6, SOCK_STREAM, IPPROTO_IP) = 7
setsockopt(7, SOL_IP, IP_BIND_ADDRESS_NO_PORT, [1], 4) = 0
bind(7, {sa_family=AF_INET6, sin6_port=htons(0), inet_pton(AF_INET6, "::1", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, 28) = 0
getsockname(7, {sa_family=AF_INET6, sin6_port=htons(0), inet_pton(AF_INET6, "::1", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, [28]) = 0
connect(7, {sa_family=AF_INET6, sin6_port=htons(57300), inet_pton(AF_INET6, "::1", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, 28) = 0
getsockname(7, {sa_family=AF_INET6, sin6_port=htons(60964), inet_pton(AF_INET6, "::1", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, [28]) = 0
I was able to bind()/connect() a million concurrent IPv4 sockets,
instead of ~32000 before patch.
lpaa23:~# ulimit -n 1000010
lpaa23:~# ./bind --connect --num-flows=1000000 &
1000000 sockets
lpaa23:~# grep TCP /proc/net/sockstat
TCP: inuse 2000063 orphan 0 tw 47 alloc 2000157 mem 66
Check that a given source port is indeed used by many different
connections :
lpaa23:~# ss -t src :40000 | head -10
State Recv-Q Send-Q Local Address:Port Peer Address:Port
ESTAB 0 0 127.0.0.2:40000 127.0.202.33:44983
ESTAB 0 0 127.0.0.2:40000 127.2.27.240:44983
ESTAB 0 0 127.0.0.2:40000 127.2.98.5:44983
ESTAB 0 0 127.0.0.2:40000 127.0.124.196:44983
ESTAB 0 0 127.0.0.2:40000 127.2.139.38:44983
ESTAB 0 0 127.0.0.2:40000 127.1.59.80:44983
ESTAB 0 0 127.0.0.2:40000 127.3.6.228:44983
ESTAB 0 0 127.0.0.2:40000 127.0.38.53:44983
ESTAB 0 0 127.0.0.2:40000 127.1.197.10:44983
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Eric Dumazet