Bug: lmtp proxy does not quote local parts with spaces

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Bug: lmtp proxy does not quote local parts with spaces

Dave-2

There seems to be a bug with RFC822 processing in ltmp proxying that doesn't
quote local parts that, for example, contain spaces.

director config:

director_username_hash = %Ln
lmtp_proxy             = yes
recipient_delimiter    = +

protocol lmtp {
        auth_socket_path       = director-userdb
        auth_username_chars    =
        auth_username_format   = %Ln
        passdb {
                driver                 = sql
                args                   = /etc/director/sql.d/lmtp.ext
                result_failure         = return-fail
                result_internalfail    = return-fail
        }
}

lmtp.ext:

password_query = SELECT 'y' AS proxy, NULL AS password, 'y' AS nopassword FROM
users WHERE userName='%Ln'

from exim -> director LMTP network dump:

MAIL FROM:<[hidden email]>\r\n
RCPT TO:<"deemzed.uk+Junk E-mail"@mailbox.localhost>\r\n
DATA\r\n
(etc)
.\r\n

501 5.5.4 Invalid parameters\r\n

QUIT\r\n

from director -> dovecot LMTP network dump:

MAIL FROM:<[hidden email]>\r\n
RCPT TO:<deemzed.uk+Junk E-mail>\r\n

501 5.5.4 Invalid.parameters\r\n

I'll try to pare down a full config for doveconf that displays this behaviour if
required, as currently I have sensitive/extraneous information in there, but
this seems fairly cut and dried as a bug to me.

--
Dave
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Re: Bug: lmtp proxy does not quote local parts with spaces

Alexander Dalloz
Am 26.10.2017 um 12:20 schrieb David Zambonini:
>
> There seems to be a bug with RFC822 processing in ltmp proxying that doesn't
> quote local parts that, for example, contain spaces.

Newer related RFCs are RFC 5321 and 5322.

[ ... ]

> MAIL FROM:<[hidden email]>\r\n
> RCPT TO:<deemzed.uk+Junk E-mail>\r\n
>
> 501 5.5.4 Invalid.parameters\r\n

That recipient address is totally invalid. It is neither just a local
part without a domain, nor a plussed address destination.

Check your setup with i.e.

RCPT TO:<"Junk E-mail"@deemzed.uk>

or

RCPT TO:<"test+Junk E-mail"@deemzed.uk>

Alexander
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Re: Bug: lmtp proxy does not quote local parts with spaces

Dave-2
On 26/10/2017 18:38, Alexander Dalloz wrote:
> Am 26.10.2017 um 12:20 schrieb David Zambonini:
>>
>> There seems to be a bug with RFC822 processing in ltmp proxying that
>> doesn't
>> quote local parts that, for example, contain spaces.
>
> Newer related RFCs are RFC 5321 and 5322.

Typo, meant to say RFC2822, which they still supercede, not that the
local-part spec has changed. :)

>
> [ ... ]
>
>> MAIL FROM:<[hidden email]>\r\n
>> RCPT TO:<deemzed.uk+Junk E-mail>\r\n
>>
>> 501 5.5.4 Invalid.parameters\r\n
>
> That recipient address is totally invalid. It is neither just a local
> part without a domain, nor a plussed address destination.
>
> Check your setup with i.e.
>
> RCPT TO:<"Junk E-mail"@deemzed.uk>
>
> or
>
> RCPT TO:<"test+Junk E-mail"@deemzed.uk>

Apologies, I was attempting to cut the config down at the time the dump
was taken. Correcting (I can provide config privately, but not share to
list), I still get:

MAIL FROM:<[hidden email]>\r\n
RCPT TO:<"deemzed.uk+Junk E-mail"@mailbox.localhost>\r\n
DATA\r\n
(etc)
.\r\n

501 5.5.4 Invalid parameters\r\n

QUIT\r\n

from director -> dovecot LMTP network dump:

MAIL FROM:<[hidden email]>\r\n
RCPT TO:<deemzed.uk+Junk [hidden email]>\r\n

501 5.5.4 Invalid.parameters\r\n

The problem is that dovecot is interpreting/unquoting the local part of
the address to insert into the username, but the client code in
client_proxy_rcpt()/address_add_detail() [lmtp/commands.c] then inserts
the username and detail directly into lmtp_rcpt.address with no attempt
whatsoever to requote that string regardless of what characters it
contains, leading to the situation where a straight-through proxy fails
as director is generating addresses that dovecot doesn't like. It can be
corrected manually using:

override_fields = destuser="%{orig_username}"@%{orig_domain}

which kind of "fixes" the issue, which I had thought sufficient last
year for the limited range of inputs I have, but it turns out to break
director hashing as the username is then hashed containing quotes (not
to mention fun with recipient_delimiter).

Looking through RFC2822 any non-atext character in username, detail or
delimiter is enough for the local part to be converted to quoted-string.
Now I've traced it through in the source, I could have a look at
starting to get a fix together tomorrow with an aim to providing a pull
request, if it turns out there are no side-effects to treating
lmtp_rcpt.address like this and you'd like an example of what I mean.

--
David Zamboninini
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Re: Bug: lmtp proxy does not quote local parts with spaces

Dave-2
On 26/10/2017 19:33, David Zambonini wrote:

> On 26/10/2017 18:38, Alexander Dalloz wrote:
>> Am 26.10.2017 um 12:20 schrieb David Zambonini:
>>>
>>> There seems to be a bug with RFC822 processing in ltmp proxying that
>>> doesn't
>>> quote local parts that, for example, contain spaces.
>>
>> Newer related RFCs are RFC 5321 and 5322.
>
> Typo, meant to say RFC2822, which they still supercede, not that the
> local-part spec has changed. :)
>
>>
>> [ ... ]
>>
>>> MAIL FROM:<[hidden email]>\r\n
>>> RCPT TO:<deemzed.uk+Junk E-mail>\r\n
>>>
>>> 501 5.5.4 Invalid.parameters\r\n
>>
>> That recipient address is totally invalid. It is neither just a local
>> part without a domain, nor a plussed address destination.
>>
>> Check your setup with i.e.
>>
>> RCPT TO:<"Junk E-mail"@deemzed.uk>
>>
>> or
>>
>> RCPT TO:<"test+Junk E-mail"@deemzed.uk>
>
> Apologies, I was attempting to cut the config down at the time the dump
> was taken. Correcting (I can provide config privately, but not share to
> list), I still get:
>
> MAIL FROM:<[hidden email]>\r\n
> RCPT TO:<"deemzed.uk+Junk E-mail"@mailbox.localhost>\r\n
> DATA\r\n
> (etc)
> .\r\n
>
> 501 5.5.4 Invalid parameters\r\n
>
> QUIT\r\n
>
> from director -> dovecot LMTP network dump:
>
> I could have a look at
> starting to get a fix together tomorrow with an aim to providing a pull
> request, if it turns out there are no side-effects to treating
> lmtp_rcpt.address like this and you'd like an example of what I mean.

My apologies for not adding your address on my initial response, Alexander - not
sure if you noticed what I replied with or not.

Nope, this isn't going to happen. I'm not familiar with the dovecot internals
but lmtp uses just the address string in the form of "full address with quotes
stripped from local part but otherwise not decoded" and nothing else throughout,
which touches on quite a bit of code. It makes it indeterminate and not always
possible to reassemble the original, it's a bit of a trainwreck.

The sanest option to me seems to me to be to store a decoded local part and
domain in addition to the detail in mail_recipient, and keeping a now properly
rfc822 encoded address in sync with it. However, this would cause a deviation
from existing behaviour for the full original user (the quotes would be seen).

I'm between a rock and a hard place here - at the very least I'd like this bug
to be officially recognised.

--
David Zambonini
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Re: Bug: lmtp proxy does not quote local parts with spaces

Dave-2

Hi again,

I've not heard anything further regarding this bug, so I've had a look at the code.

To restate the bug in a more precise way: LMTP in dovecot treats external RFC822
email addresses in the envelope recipient and internal usernames as almost
identical/interchangeable. This is incorrect and leads to issues when attempting
to use director as an LMTP proxy to proxy to recipients with quoted-local parts,
as it is issuing invalid email addresses at the LMTP protocol level (it strips
quotes from the local part and then does not add them again when proxying). It's
also causing issues with director username hashing.

I've created a "bugfix" patch to indicate what I mean, it appears to solve the
issue, although I do not think it is anywhere near a production ready change.

1. The first problem is that dovecot is not performing a full decode on the
envelope recipient address when creating the username, leading to escaped
characters left in escaped form, and is not treating it consistently, choosing
to either strip the surrounding quotes or not depending on whether or not it
contains an @. I've fixed this by changing the code in lmtp_unescape_address()
[src/lmtp/commands.c] to use rfc822_parse_quoted_string().

2. This leads to the second problem where the username becomes ambiguous if the
local-part contains an @ (regardless of whether or not the first fix is applied
or not). I've worked around this by using strrchr() instead of strchr() on the
username string to split the domain out in mail_user_hash()
[src/lib-mail/mail-user-hash.c] and message_detail_address_parse()
[src/lib-mail/message-address.c], although likely I've missed some place this
change should be made.

3. The third problem is then re-encoding the username in the envelope recipient
when proxying, which was not done at all. I've added a function
lmtp_client_rfc822_escape_address(), which is similar to
str_append_maybe_escape() to escape the address at protocol time in
lmtp_client_send_rcpts() [src/lib-smtp/lmtp-client.c], although I suspect it
should be done earlier, this is just a working proof.

The other reason I don't believe this patch is production quality is that I have
not examined any interaction between these changes and sieve's use of the
envelope recipient. I'm hoping that a developer can chip in here? (hint!)

(Apologies for top posting)

On 30/10/2017 13:18, David Zambonini wrote:

> On 26/10/2017 19:33, David Zambonini wrote:
>> On 26/10/2017 18:38, Alexander Dalloz wrote:
>>> Am 26.10.2017 um 12:20 schrieb David Zambonini:
>>>>
>>>> There seems to be a bug with RFC822 processing in ltmp proxying that
>>>> doesn't
>>>> quote local parts that, for example, contain spaces.
>>>
>>> Newer related RFCs are RFC 5321 and 5322.
>>
>> Typo, meant to say RFC2822, which they still supercede, not that the
>> local-part spec has changed. :)
>>
>>>
>>> [ ... ]
>>>
>>>> MAIL FROM:<[hidden email]>\r\n
>>>> RCPT TO:<deemzed.uk+Junk E-mail>\r\n
>>>>
>>>> 501 5.5.4 Invalid.parameters\r\n
>>>
>>> That recipient address is totally invalid. It is neither just a local
>>> part without a domain, nor a plussed address destination.
>>>
>>> Check your setup with i.e.
>>>
>>> RCPT TO:<"Junk E-mail"@deemzed.uk>
>>>
>>> or
>>>
>>> RCPT TO:<"test+Junk E-mail"@deemzed.uk>
>>
>> Apologies, I was attempting to cut the config down at the time the dump
>> was taken. Correcting (I can provide config privately, but not share to
>> list), I still get:
>>
>> MAIL FROM:<[hidden email]>\r\n
>> RCPT TO:<"deemzed.uk+Junk E-mail"@mailbox.localhost>\r\n
>> DATA\r\n
>> (etc)
>> .\r\n
>>
>> 501 5.5.4 Invalid parameters\r\n
>>
>> QUIT\r\n
>>
>> from director -> dovecot LMTP network dump:
>>
>> I could have a look at
>> starting to get a fix together tomorrow with an aim to providing a pull
>> request, if it turns out there are no side-effects to treating
>> lmtp_rcpt.address like this and you'd like an example of what I mean.
>
> My apologies for not adding your address on my initial response, Alexander - not
> sure if you noticed what I replied with or not.
>
> Nope, this isn't going to happen. I'm not familiar with the dovecot internals
> but lmtp uses just the address string in the form of "full address with quotes
> stripped from local part but otherwise not decoded" and nothing else throughout,
> which touches on quite a bit of code. It makes it indeterminate and not always
> possible to reassemble the original, it's a bit of a trainwreck.
>
> The sanest option to me seems to me to be to store a decoded local part and
> domain in addition to the detail in mail_recipient, and keeping a now properly
> rfc822 encoded address in sync with it. However, this would cause a deviation
> from existing behaviour for the full original user (the quotes would be seen).
>
> I'm between a rock and a hard place here - at the very least I'd like this bug
> to be officially recognised.
--
David Zambonini

dovecot-2.2.33.2-fix-quoted-local.patch (7K) Download Attachment
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Re: Bug: lmtp proxy does not quote local parts with spaces

Stephan Bosch-2
Hi,

Sorry, we're in a bit of a v2.3 merge frenzy. Much of the LMTP code will
be replaced in v2.3, but I'll give the  older code a look as well.

This can take a while though.

Regards,

Stephan.



Op 1-11-2017 om 18:34 schreef David Zambonini:

> Hi again,
>
> I've not heard anything further regarding this bug, so I've had a look at the code.
>
> To restate the bug in a more precise way: LMTP in dovecot treats external RFC822
> email addresses in the envelope recipient and internal usernames as almost
> identical/interchangeable. This is incorrect and leads to issues when attempting
> to use director as an LMTP proxy to proxy to recipients with quoted-local parts,
> as it is issuing invalid email addresses at the LMTP protocol level (it strips
> quotes from the local part and then does not add them again when proxying). It's
> also causing issues with director username hashing.
>
> I've created a "bugfix" patch to indicate what I mean, it appears to solve the
> issue, although I do not think it is anywhere near a production ready change.
>
> 1. The first problem is that dovecot is not performing a full decode on the
> envelope recipient address when creating the username, leading to escaped
> characters left in escaped form, and is not treating it consistently, choosing
> to either strip the surrounding quotes or not depending on whether or not it
> contains an @. I've fixed this by changing the code in lmtp_unescape_address()
> [src/lmtp/commands.c] to use rfc822_parse_quoted_string().
>
> 2. This leads to the second problem where the username becomes ambiguous if the
> local-part contains an @ (regardless of whether or not the first fix is applied
> or not). I've worked around this by using strrchr() instead of strchr() on the
> username string to split the domain out in mail_user_hash()
> [src/lib-mail/mail-user-hash.c] and message_detail_address_parse()
> [src/lib-mail/message-address.c], although likely I've missed some place this
> change should be made.
>
> 3. The third problem is then re-encoding the username in the envelope recipient
> when proxying, which was not done at all. I've added a function
> lmtp_client_rfc822_escape_address(), which is similar to
> str_append_maybe_escape() to escape the address at protocol time in
> lmtp_client_send_rcpts() [src/lib-smtp/lmtp-client.c], although I suspect it
> should be done earlier, this is just a working proof.
>
> The other reason I don't believe this patch is production quality is that I have
> not examined any interaction between these changes and sieve's use of the
> envelope recipient. I'm hoping that a developer can chip in here? (hint!)
>
> (Apologies for top posting)
>
> On 30/10/2017 13:18, David Zambonini wrote:
>> On 26/10/2017 19:33, David Zambonini wrote:
>>> On 26/10/2017 18:38, Alexander Dalloz wrote:
>>>> Am 26.10.2017 um 12:20 schrieb David Zambonini:
>>>>> There seems to be a bug with RFC822 processing in ltmp proxying that
>>>>> doesn't
>>>>> quote local parts that, for example, contain spaces.
>>>> Newer related RFCs are RFC 5321 and 5322.
>>> Typo, meant to say RFC2822, which they still supercede, not that the
>>> local-part spec has changed. :)
>>>
>>>> [ ... ]
>>>>
>>>>> MAIL FROM:<[hidden email]>\r\n
>>>>> RCPT TO:<deemzed.uk+Junk E-mail>\r\n
>>>>>
>>>>> 501 5.5.4 Invalid.parameters\r\n
>>>> That recipient address is totally invalid. It is neither just a local
>>>> part without a domain, nor a plussed address destination.
>>>>
>>>> Check your setup with i.e.
>>>>
>>>> RCPT TO:<"Junk E-mail"@deemzed.uk>
>>>>
>>>> or
>>>>
>>>> RCPT TO:<"test+Junk E-mail"@deemzed.uk>
>>> Apologies, I was attempting to cut the config down at the time the dump
>>> was taken. Correcting (I can provide config privately, but not share to
>>> list), I still get:
>>>
>>> MAIL FROM:<[hidden email]>\r\n
>>> RCPT TO:<"deemzed.uk+Junk E-mail"@mailbox.localhost>\r\n
>>> DATA\r\n
>>> (etc)
>>> .\r\n
>>>
>>> 501 5.5.4 Invalid parameters\r\n
>>>
>>> QUIT\r\n
>>>
>>> from director -> dovecot LMTP network dump:
>>>
>>> I could have a look at
>>> starting to get a fix together tomorrow with an aim to providing a pull
>>> request, if it turns out there are no side-effects to treating
>>> lmtp_rcpt.address like this and you'd like an example of what I mean.
>> My apologies for not adding your address on my initial response, Alexander - not
>> sure if you noticed what I replied with or not.
>>
>> Nope, this isn't going to happen. I'm not familiar with the dovecot internals
>> but lmtp uses just the address string in the form of "full address with quotes
>> stripped from local part but otherwise not decoded" and nothing else throughout,
>> which touches on quite a bit of code. It makes it indeterminate and not always
>> possible to reassemble the original, it's a bit of a trainwreck.
>>
>> The sanest option to me seems to me to be to store a decoded local part and
>> domain in addition to the detail in mail_recipient, and keeping a now properly
>> rfc822 encoded address in sync with it. However, this would cause a deviation
>> from existing behaviour for the full original user (the quotes would be seen).
>>
>> I'm between a rock and a hard place here - at the very least I'd like this bug
>> to be officially recognised.
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Re: Bug: lmtp proxy does not quote local parts with spaces

Dave-2
On 03/11/2017 11:48, Stephan Bosch wrote:
> Hi,
>
> Sorry, we're in a bit of a v2.3 merge frenzy. Much of the LMTP code will be
> replaced in v2.3, but I'll give the  older code a look as well.
>
> This can take a while though.

Thank you very much for getting back to me, I can appreciate it can get hectic,
and I don't wish to appear ungrateful, I wholeheartedly endorse/recommend
dovecot and the company I work for does use paid for OX elsewhere. For my own
part, the platform I manage is > 300,000 mailboxes and dovecot performs
incredibly well.

I came up with some much smaller patches that accomplish the same thing in v2.2
using built-in functions and pushing the re-encoding slightly further up the
call stack - address/username being interchangeable over most of the lmtp code
makes significant changes problematic, so I thought it best not to try a rework.

Looking at gitub, though, I don't see any significant changes in behaviour as
far as the problem I'm seeing goes, which is worrying.

What I'll do is leave the patches here for reference, and pick this up again
after the v2.3 release. If you do have time for a further response, I could also
provide them as pull requests against current on github if you'd like to request
that.

1. Cut on the final instead of initial @ when splitting user/domain parts in
LMTP, this can fix some issues where localpart contains a quoted @:

dovecot-2.2.33.2-reverse-domaincut.patch

2. Fully decode local part on receipt in LMTP, and re-encode when proxying. This
fixes the issue where quoted local quotes are stripped on proxy, preventing
successful proxying, and some director hashing problems (exposes
str_append_maybe_escape in message-address.h, some logging is still
inconsistent, though, but would require a major rework):

dovecot-2.2.33.2-quoted-local-proxy.patch

--
David Zambonini

dovecot-2.2.33.2-quoted-local-proxy.patch (4K) Download Attachment
dovecot-2.2.33.2-reverse-domaincut.patch (1K) Download Attachment
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Re: Bug: lmtp proxy does not quote local parts with spaces

Stephan Bosch-2


Op 3-11-2017 om 15:25 schreef David Zambonini:

> On 03/11/2017 11:48, Stephan Bosch wrote:
>> Hi,
>>
>> Sorry, we're in a bit of a v2.3 merge frenzy. Much of the LMTP code will be
>> replaced in v2.3, but I'll give the  older code a look as well.
>>
>> This can take a while though.
> Thank you very much for getting back to me, I can appreciate it can get hectic,
> and I don't wish to appear ungrateful, I wholeheartedly endorse/recommend
> dovecot and the company I work for does use paid for OX elsewhere. For my own
> part, the platform I manage is > 300,000 mailboxes and dovecot performs
> incredibly well.
>
> I came up with some much smaller patches that accomplish the same thing in v2.2
> using built-in functions and pushing the re-encoding slightly further up the
> call stack - address/username being interchangeable over most of the lmtp code
> makes significant changes problematic, so I thought it best not to try a rework.
>
> Looking at gitub, though, I don't see any significant changes in behaviour as
> far as the problem I'm seeing goes, which is worrying.

These changes still live in a feature branch.

Regards,

Stephan.