BIND 10 #838: "string iterator is not dereferencable" issue

[BIND 10 Development]

#838: "string iterator is not dereferencable" issue
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                   Reporter:         |                 Owner:  jinmei
  fdupont                            |                Status:  reviewing
                       Type:         |             Milestone:
  defect                             |  Sprint-20110517
                   Priority:  major  |            Resolution:
                  Component:         |             Sensitive:  0
  Unclassified                       |           Sub-Project:  DNS
                   Keywords:         |  Estimated Difficulty:  0.0
            Defect Severity:  N/A    |           Total Hours:  0
Feature Depending on Ticket:         |
        Add Hours to Ticket:  0      |
                  Internal?:  0      |
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Comment (by ocean):

 Replying to [comment:14 jinmei]:
 > Another quick question: the change committed in the branch modified
 > EncodeNormalizer::operator*(), while the original proposed fix was
 > about DecodeNormalizer::operator*().  Could you clarify it?  Is that a
 > typo of the original proposed fix, or did you find the original report
 > was wrong and the problem was actually in and only in
 > EncodeNormalizer?
 >
 Sorry, it's my fault. it should be put in {{{DecodeNormalizer}}}, this is
 not needed to put
 into {{{EncodeNormalizer}}}. I cannot commit the change on the Windows
 platform because a lot
 of hacks are made to reproduce this. So we'd better put the windows
 related changes into the trunk.

 > In any case, lacking the environment, it's not very clear to me what
 > is exactly wrong with the original implementation (calling operator*
 > at the end() of the data is wrong of course, but I don't understand
 > how that situation happened).  Please explain more details about the
 > problem.
 >
 > Thanks,

 This is triggered by the following sequence.
 1. Given input string of " " which is a one char string with 0x20 (the
 space) character.
 2. Call decodeBase32Hex-> Base32HexTransformer::decode->
 {{{
         result.assign(Decoder(DecodeNormalizer(BaseZeroCode,
 input.begin(),
                                                srit.base(), input.end())),
                       Decoder(DecodeNormalizer(BaseZeroCode, input.end(),
                                                input.end(),
 input.end())));
 }}}
 3. The {{{DecodeNormalizer()}}} is a iterator with base_ points to the
 start of string.
 4. When later the {{{result.assign()}}} is called, it will increase the
 first iterator and try to dereference it.
 {{{
     DecodeNormalizer& operator++() {
         ++base_;
         while (base_ != base_end_ && isspace(*base_)) {
             ++base_;
         }
         if (base_ == base_beginpad_) {
             in_pad_ = true;
         }

         return (*this);
     }
 }}}
 Initially the base_ is point to the begin of the input string, since
 {{{*base_}}} is a space character (0x20), the base_ will be increased by 1
 and equal to {{{base_end_}}}
 5. Later when the iterator is dereferenced, it will trigger this problem.

 I tried to fix it in the {{{operator++()}}} function, but it seems that no
 appropriate method.

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Ticket URL: <http://bind10.isc.org/ticket/838#comment:15>
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