[tor-bugs] #33889 [Core Tor/Tor]: Functions with char* arguments are dangerous when used with casting

[Tor Bug Tracker & Wiki]

#33889: Functions with char* arguments are dangerous when used with casting
------------------------------+------------------------------------
     Reporter:  asn           |      Owner:  (none)
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.4.4.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  security memory-safety
Actual Points:                |  Parent ID:
       Points:  3             |   Reviewer:
      Sponsor:                |
------------------------------+------------------------------------
 There are various functions in our codebase which receive char* arguments
 when they actually receive a byte array. That's I guess because of the old
 C standard when uint8_t didn't really exist, so we had to use char* for
 everything.

 Still, these days we use uint8_t* and this means that we need to cast it
 to char* when we use those functions. This can cause security issues
 because this casting is silencing type-safety warnings (as an example see
 https://github.com/torproject/tor/pull/1843#discussion_r406191281).

 For example, see how `fast_mem_is_zero()` is used 75% of the time with
 casting its first argument. Instead of doing this, we could make a new
 `fast_mem_is_zero_uint8t()` function that takes uint8_t as argument. Or
 even make a `fast_mem_is_zero_char()` function that takes char*.

 In other functions, it might be possible to replace the `char*` with
 `void*` but in the case of `fast_mem_is_zero()` that's not possible
 because of the implementation of the function.

 Other potential problem functions: `base64_encode()` `hex_str()`
 `crypto_rand()` `crypto_digest()`.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/33889>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online