dnscrypt making init/1 - systemd listen on port 53 tcp/udp

r0b0t · 2017-08-20 21:25:53

Hi guys,
I'm not sure if this is normal or not but it's worth for a discussion.
After I set up dnscrypt-proxy , I noticed that whenever the service was started init/1 was listening on port 53 tcp/udp

udp        0      0 127.0.0.1:53            0.0.0.0:*                           1/init 
tcp        0      0 127.0.0.1:53            0.0.0.0:*               LISTEN      1/init

By checking with strace I see when it creates the socket.

23:13:52.539024 socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, IPPROTO_IP) = 102 <0.000015>
23:13:52.539064 setsockopt(102, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 <0.000010>
23:13:52.539098 bind(102, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("127.0.0.1")}, 16) = 0 <0.000015>
23:13:52.539146 listen(102, 128)        = 0 <0.000010>
23:13:52.539179 socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, IPPROTO_IP) = 103 <0.000011>
23:13:52.539212 setsockopt(103, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 <0.000009>
23:13:52.539245 bind(103, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("127.0.0.1")}, 16) = 0 <0.000012>

Is this normal at all??
I don't feel comfortable at all having the main system process in listening, what are your thoughts?
thanks.

Last edited by r0b0t (2017-08-20 21:27:27)

brebs · 2017-08-20 22:59:29

Show the command you used, to get "1/init".

r0b0t · 2017-08-20 23:31:27

I think what strace shows is enough to get the point as if you run systemctl start dnscrypt-proxy you will see that the socket will be created.
In any case the command would be something like

# netstat -patuln | grep init
tcp        0      0 127.0.0.1:53            0.0.0.0:*               LISTEN      1/init              
udp        0      0 127.0.0.1:53            0.0.0.0:*                           1/init      

# systemctl stop dnscrypt-proxy
Warning: Stopping dnscrypt-proxy.service, but it can still be activated by:
  dnscrypt-proxy.socket
[root@i]# netstat -patuln | grep init
tcp        0      0 127.0.0.1:53            0.0.0.0:*               LISTEN      1/init              
udp        0      0 127.0.0.1:53            0.0.0.0:*                           1/init              
[root@i]# systemctl stop dnscrypt-proxy.socket
[root@i]# netstat -patuln | grep init
[root@i]#

Last edited by r0b0t (2017-08-20 23:31:42)

r0b0t · 2017-08-20 23:52:22

I understand what you mean by your question, here some more info:

lsof -i -a -p 1
COMMAND PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
systemd   1 root  103u  IPv4 112878      0t0  TCP localhost.localdomain:domain (LISTEN)
systemd   1 root  104u  IPv4 112879      0t0  UDP localhost.localdomain:domain 
ls -aclh /proc/1/fd/103 
lrwx------ 1 root root 64 Aug 20 23:15 /proc/1/fd/103 -> socket:[112878]
ls -aclh /proc/1/fd/104
lrwx------ 1 root root 64 Aug 21 01:37 /proc/1/fd/104 -> socket:[112879]

cat /proc/1/net/tcp | grep 112878
   1: 0100007F:0035 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 112878 1 ffff9418529a4d80 99 0 0 10 5           
 cat /proc/1/net/udp | grep 112879
 5035: 0100007F:0035 00000000:0000 07 00000000:00000000 00:00000000 00000000     0        0 112879 2 ffff9417d00192c0 0

Last edited by r0b0t (2017-08-21 00:01:56)

seiichiro0185 · 2017-08-21 08:27:29

Could it be that some kind of Systemd Socket Activation is used here? in that case Systemd would open the Port and launch the actual daemon on incoming requests (This is just a shot in the dark, I didn't take a look at dnscrypt yet). If this is the case there should be a dnscrypt-proxy.socket file somewhere (most likely /usr/lib/systemd/system/) that defines it.

Last edited by seiichiro0185 (2017-08-21 08:29:41)

r0b0t · 2017-08-23 08:49:08

cat /usr/lib/systemd/system/dnscrypt-proxy.socket
[Unit]
Description=dnscrypt-proxy listening socket

[Socket]
ListenStream=127.0.0.1:53
ListenDatagram=127.0.0.1:53

[Install]
WantedBy=sockets.target

So I guess this is "normal"...

Arch Linux

#1 2017-08-20 21:25:53

dnscrypt making init/1 - systemd listen on port 53 tcp/udp

#2 2017-08-20 22:59:29

Re: dnscrypt making init/1 - systemd listen on port 53 tcp/udp

#3 2017-08-20 23:31:27

Re: dnscrypt making init/1 - systemd listen on port 53 tcp/udp

#4 2017-08-20 23:52:22

Re: dnscrypt making init/1 - systemd listen on port 53 tcp/udp

#5 2017-08-21 08:27:29

Re: dnscrypt making init/1 - systemd listen on port 53 tcp/udp

#6 2017-08-23 08:49:08

Re: dnscrypt making init/1 - systemd listen on port 53 tcp/udp

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