[tor-bugs] #18938 [Core Tor/Tor]: Authorities should reject non-ASCII content in ExtraInfo descriptors

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#18938: Authorities should reject non-ASCII content in ExtraInfo descriptors
-------------------------------------------------+-------------------------
 Reporter:  teor                                 |          Owner:  neel
     Type:  defect                               |         Status:
                                                 |  assigned
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  unspecified
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  needs-proposal, tor-dirauth, needs-  |  Actual Points:
  spec, easy, 034-triage-20180328,               |
  034-removed-20180328                           |
Parent ID:  #24033                               |         Points:  1
 Reviewer:                                       |        Sponsor:
-------------------------------------------------+-------------------------

Old description:

> In #18656, we discovered that authorities don't validate that ExtraInfo
> descriptors are printable ASCII before accepting them.
>
> Authorities (and HSDirs) should check every directory document they
> receive consists only of "printing ASCII", as defined in torspec:
> {{{
>     NL = The ascii LF character (hex value 0x0a).
>     KeywordChar ::= 'A' ... 'Z' | 'a' ... 'z' | '0' ... '9' | '-'
>     ArgumentChar ::= any printing ASCII character except NL.
>     WS = (SP | TAB)+
> }}}
>
> I've heard others say that the following lines allow non-ASCII content,
> but I'm not sure if that's actually the case, and if it is, how many
> relays this would affect:
> * the "platform" line in relay descriptors, which is a "human-readable
> string",
> * the contact "info" line in relay descriptors, which has an undefined
> format.
>
> If it is, I'd recommend we make them all ASCII for consistency, and
> update torspec to clarify, and include it as a "major" change in an 0.2.x
> tor release.
>
> (This means that some users will be unable to spell their names
> correctly. But there was never any guarantee that 8-bit characters in
> "info" would be interpreted as users intended. I think security is more
> important here.)

New description:

 In #18656, we discovered that authorities don't validate that ExtraInfo
 descriptors are printable ASCII before accepting them.

 Authorities (and HSDirs) should check every ~~directory~~ extrainfo
 document they receive consists only of "printing ASCII", as defined in
 torspec:
 {{{
     NL = The ascii LF character (hex value 0x0a).
     KeywordChar ::= 'A' ... 'Z' | 'a' ... 'z' | '0' ... '9' | '-'
     ArgumentChar ::= any printing ASCII character except NL.
     WS = (SP | TAB)+
 }}}

 I've heard others say that the following lines allow non-ASCII content,
 but I'm not sure if that's actually the case, and if it is, how many
 relays this would affect:
 * the "platform" line in relay descriptors, which is a "human-readable
 string",
 * the contact "info" line in relay descriptors, which has an undefined
 format.

 Edit: allowing users to spell their names correctly is important. That's
 why we'll use utf-8 for relay descriptors, votes, and consensuses.

 ~~If it is, I'd recommend we make them all ASCII for consistency, and
 update torspec to clarify, and include it as a "major" change in an 0.2.x
 tor release.

 (This means that some users will be unable to spell their names correctly.
 But there was never any guarantee that 8-bit characters in "info" would be
 interpreted as users intended. I think security is more important here.)~~

--

Comment (by teor):

 Change description based on prop285 utf-8 support.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18938#comment:34>
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