SOCK_STREAM socket + bind without calling listen makes address hidden

[Manvendra Bhangui]

Stumbled on  an issue of  imap server refusing to start on TCP port
993 with error EADDRINUSE inspite of netstat, lsof, ss programs
indicating no process has bound on tcp port 993

On debugging found the issue to be with portreserve program.
http://linux.die.net/man/1/portreserve

But portreserve is not the issue. It is doing what it is expected to
do - grab and reserve a port

None of the programs - netstat, lsof, ss could show that the
portreserve port has bound on the socket 993. Killing the portreserve
program or calling portrelease program resolves the issue.

I can simulate the same issue by writing a code which just calls
socket() and bind() and nothing that I know of can find out which
program has bound on an address

Shouldn't there be a socket state which netstat / lsof / ss can reveal
which process has bound on an address without calling listen()? I
could think of rogue programs which calls socket() + bind(), without
calling listen(), to prevent programs from starting up and left with a
clueless admin trying to figure out which process has bound an address

start portreserve service to reserve imaps port

# systemctl enable portreserve

## get the pid of portreserve
# ps -ef|grep portreserve
root     29771     1  0 11:14 ?        00:00:00 /sbin/portreserve
root     29773 28654  0 11:14 pts/1    00:00:00 grep --color=auto portreserve

run lsof to find all open ports. You can see that for TCP socket, the
address is not shown.
it just shows "protocol: TCP"
For UDP it shows the address

# lsof -p 29771
lsof: WARNING: can't stat() fuse.gvfsd-fuse file system /run/user/1000/gvfs
      Output information may be incomplete.
COMMAND     PID USER   FD   TYPE             DEVICE SIZE/OFF    NODE NAME
portreser 29771 root  cwd    DIR              253,0     4096       2 /
portreser 29771 root  rtd    DIR              253,0     4096       2 /
portreser 29771 root  txt    REG              253,0    15792 2112388
/usr/sbin/portreserve
portreser 29771 root  mem    REG              253,0    62072 2109005
/usr/lib64/libnss_files-2.20.so
portreser 29771 root  mem    REG              253,0  2082456 2101348
/usr/lib64/libc-2.20.so
portreser 29771 root  mem    REG              253,0   163176 2098678
/usr/lib64/ld-2.20.so
portreser 29771 root    0uW  REG               0,19        6  175038
/run/portreserve.pid
portreser 29771 root    1u  unix 0xffff8801fd24c600      0t0  175039
/var/run/portreserve/socket
portreser 29771 root    4u  sock                0,8      0t0  175043
protocol: TCP
portreser 29771 root    5u  IPv4             175044      0t0     UDP *:imaps

same with the netstat program which shows only the udp port

# netstat -anp |grep 993
udp        0      0 0.0.0.0:993             0.0.0.0:*
         29771/portreserve

same with the ss program which also shows only the udp port
# ss -a| egrep "993|imaps"
udp    UNCONN     0      0                    *:ipproto-993               *:*


try is a simple program which binds on both tcp port 993 (ipv4 as well as ipv6)

# ./try
bind: Address already in use
#

socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 3
setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
setsockopt(3, SOL_SOCKET, SO_LINGER, {onoff=1, linger=60}, 8) = 0
bind(3, {sa_family=AF_INET, sin_port=htons(993),
sin_addr=inet_addr("0.0.0.0")}, 16) = -1 EADDRINUSE (Address already
in use)
close(3)                                = 0
socket(PF_INET6, SOCK_STREAM, IPPROTO_TCP) = 3
setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
setsockopt(3, SOL_SOCKET, SO_LINGER, {onoff=1, linger=60}, 8) = 0
bind(3, {sa_family=AF_INET6, sin6_port=htons(993), inet_pton(AF_INET6,
"::", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, 28) = -1
EADDRINUSE (Address already in use)

-- 
Regards Manvendra - http://www.indimail.org
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