How to kill one TCP connection in Linux?

Question

I have a process that opens multiple tcp connections to multiple browsers on separate ports.

Using netsat, the output looks something like this:

tcp 0 0 server1.something:myprog client1.something:49987 ESTABLISHED tcp 0 0 server1.something:myprog client1.something:65987 ESTABLISHED tcp 0 0 server1.something:myprog client1.something:89987 ESTABLISHED 

Now I would like to kill exactly one of the compounds? How can I do it? (Since killing the process will destroy all connections)

Answer 1

Here are a few options:

• Join gdb and call the close () function on fd. You can map from addr / port to the inode number via / proc / net / tcp and from the inode number to FD inside the process using ls -la / proc / $ pid / fd.
• Trick the RST package. You will need to generate it locally and guess the SEQ number in some way.
• Perhaps configure the iptables rule to generate RST for the next package.
• Write the kernel module.

It seems that this is not supported well. Processes are likely to crash if their FDs are unexpectedly closed anyway.

Answer 2

You cannot kill one process connection.

But you can block it with iptables. Thus, the connection cannot provide or receive data, and the client will time out.

Answer 3

In the Linux kernel> = 4.9 you can use the ss command from iproute2 with the -K switch

 ss -K dst client1.something dport = 49987 

the kernel must be compiled with the CONFIG_INET_DIAG_DESTROY option CONFIG_INET_DIAG_DESTROY .