[tor-bugs] #34400 [Core Tor/Tor]: control: HSFETCH command fails to validate v2 addresses

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#34400: control: HSFETCH command fails to validate v2 addresses
-------------------------+-------------------------------------------------
     Reporter:  dgoulet  |      Owner:  (none)
         Type:  defect   |     Status:  new
     Priority:  Medium   |  Milestone:  Tor: 0.4.5.x-final
    Component:  Core     |    Version:
  Tor/Tor                |   Keywords:  044-backport 043-backport
     Severity:  Normal   |  042-backport tor-hs tor-control regression
Actual Points:           |  Parent ID:
       Points:  0.1      |   Reviewer:
      Sponsor:           |
-------------------------+-------------------------------------------------
 In `handle_control_hsfetch()`:

 {{{
   } else if (strcmpstart(arg1, v2_str) == 0 &&
              rend_valid_descriptor_id(arg1 + v2_str_len) &&
              base32_decode(digest, sizeof(digest), arg1 + v2_str_len,
                            REND_DESC_ID_V2_LEN_BASE32) ==
                 REND_DESC_ID_V2_LEN_BASE32) {
 }}}

 The above snippet is how we validate the v2 address for the `HSFETCH`
 command. The `base32_decode()` function returns the number of bytes
 _decoded_ and thus it should returns on success `sizeof(digest)`, not the
 total length of the base32 address (20 vs 32).

 Issue was introduced in commit `a517daa56f5848d25ba79617a1a7b82ed2b0a7c0`
 meaning since 0.4.1.1-alpha (ticket #28913).

 I noticed this because I recently updated the bad HSDirscanner Tor to use
 our latest and it broke the scanner.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/34400>
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