[gentoo-user] Bash & Server Sockets

[Hilco Wijbenga <hilco.wijbenga@gmail.com>]

Hi all,

In Bash /dev/tcp/host/port can be used to write to a TCP socket. This
works nicely so I was very curious whether it would work the other way
too: is it possible to have a Bash script listen on a particular port
as if it were a server? I couldn't find anything in the Bash manual
about it. Google does find a few examples but they all use nc. But
that's cheating! ;-) Is it possible with just Bash, no extra tools?
(If yes, please enlighten me as to how, obviously I could not get it
to work.)

On a related note, I read some comments about Debian having /dev/tcp
disabled in Bash because of security concerns. Would someone
knowledgeable about security be able to comment on that? It doesn't
make much sense to me. I mean, any Perl, Python, Ruby, etcetera script
can write to a socket. Even Debian (with every option deselected)
comes installed with Perl. (Yes, I installed Debian just to find out!)
:-) So why should /dev/tcp in Bash be deemed such a security risk?

Cheers,
Hilco

P.S. For the curious:
#!/bin/bash
exec 3<>/dev/tcp/www.google.ca/80
echo -ne "GET / HTTP/1.1\r\n">&3
echo -ne "Host: www.google.ca\r\n">&3
echo -ne "Connection: close\r\n">&3
echo -ne "\r\n">&3
cat <&3