dovecot - Mar 2010 - Improper use of IN-USE in case of a failed authentication

RFC2449 defines the IN-USE extended POP3 response code as

	8.1.2.  The IN-USE response code

	This occurs on an -ERR response to an AUTH, APOP, or PASS
	command.  It indicates the authentication was successful, but
	the user's maildrop is currently in use (probably by another
	POP3 client).
	http://www.faqs.org/rfcs/rfc2449.html

In contrast to this, the POP3 login code in client_authenticate.c will
send IN-USE whenever authentication was not successful because of
some kind of internal failure[*].

	[*] Noticed during experiments with a shell SQL database
	driver which only ever returns errors as reaction to any
	query.

I happen to know of at least one (partial) client implementation (I
happen to have written which is used by an iPhone application for POP3
user credential verification) which actually interprets IN-USE as
it is defined by the RFC.

On Sun, 2010-03-28 at 23:09 +0200, Rainer Weikusat
wrote:
> RFC2449 defines the IN-USE extended POP3 response code as
> 
> 	8.1.2.  The IN-USE response code
> 
> 	This occurs on an -ERR response to an AUTH, APOP, or PASS
> 	command.  It indicates the authentication was successful, but
> 	the user's maildrop is currently in use (probably by another
> 	POP3 client).
> 	http://www.faqs.org/rfcs/rfc2449.html
> 
> In contrast to this, the POP3 login code in client_authenticate.c will
> send IN-USE whenever authentication was not successful because of
> some kind of internal failure[*].
Yes. In both cases the failure is temporary.
> I happen to know of at least one (partial) client implementation (I
> happen to have written which is used by an iPhone application for POP3
> user credential verification) which actually interprets IN-USE as
> it is defined by the RFC.
What about the reverse? If no IN-USE is sent, how many clients will just
treat it as authentication failure and ask the user for the password
again, without showing the "internal failure" error at all? (I
don't
know the answer. I assumed IN-USE would cause less problems.)
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 198 bytes
Desc: This is a digitally signed message part
URL:
<http://dovecot.org/pipermail/dovecot/attachments/20100329/8ec7f9f5/attachment-0002.bin>

Timo Sirainen <tss at iki.fi> writes:
> On Sun, 2010-03-28 at 23:09 +0200, Rainer Weikusat wrote:
>> RFC2449 defines the IN-USE extended POP3 response code as
>> 
>> 	8.1.2.  The IN-USE response code
>> 
>> 	This occurs on an -ERR response to an AUTH, APOP, or PASS
>> 	command.  It indicates the authentication was successful, but
>> 	the user's maildrop is currently in use (probably by another
>> 	POP3 client).
>> 	http://www.faqs.org/rfcs/rfc2449.html
>> 
>> In contrast to this, the POP3 login code in client_authenticate.c will
>> send IN-USE whenever authentication was not successful because of
>> some kind of internal failure[*].
>
> Yes. In both cases the failure is temporary.
The RFC excerpt above states that "It indicates the authentication was
successful but the users' maildrop is currently in use". The
difference arguably doesn't matter much for the intended purpose of the
response code, namely, provide a more reliably way to check for
'mailbox locked' states than trying to analyze the 'user
message' part
of the string, it just means that IN-USE does not communicate anything
about the validity of the credentials which were being used.