openssh unix dev - Nov 2001 - patch for problem with "Bind to port 22 on 0.0.0.0 failed: Address already in use."

Hi,

  there is a cosmetic problem in openssh (all versions AFAIK):

When you start sshd with no "ListenAddress" lines in sshd_config, it
tries to bind address "::" (successfuly) and then "0.0.0.0"
and it fails
with "Address already in use". Moreover it can happen that
"0.0.0.0" is in
addr list sooner than "::" so sshd than will listen only on ipv4
address
"0.0.0.0".

  I have prepared patch for 3.0.1p1 which should solve both problems - I go 
throught the list and when there are both "0.0.0.0" and "::"
on the same
port, I remove "0.0.0.0" from the list.

  I have also removed condition from 'error("Bind to ....")'.
When you have
two "ListenAddress" lines in sshd_config, one is wrong and the wrong
one is
tested before the good one, no error is logged.

  Can you look on it and maybe include it to next version, please?

  Thanks

-- 
Mgr. Jan Cihlar
developer
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On Tue, 27 Nov 2001, Jan Cihlar wrote:
>   there is a cosmetic problem in openssh (all versions AFAIK):
> 
> When you start sshd with no "ListenAddress" lines in sshd_config,
it
> tries to bind address "::" (successfuly) and then
"0.0.0.0" and it fails
> with "Address already in use". Moreover it can happen that
"0.0.0.0" is in
> addr list sooner than "::" so sshd than will listen only on ipv4
address
> "0.0.0.0".
This is a Linuxism; binding with standard kernel to both '::' and 
'0.0.0.0' will fail.  This is because '::' already accepts IPv4 
connections though mapped addresses.  Double-binding is not possible as 
with IPv6.

Just work around this by listening to :: only, if you have to.  It's best 
to leave ListenAddress empty.

-- 
Pekka Savola                 "Tell me of difficulties surmounted,
Netcore Oy                   not those you stumble over and fall"
Systems. Networks. Security.  -- Robert Jordan: A Crown of Swords