Beefy Boxes and Bandwidth Generously Provided by pair Networks
Just another Perl shrine
 
PerlMonks  

Re^5: Hash key composition with a comma?

by LanX (Archbishop)
on Mar 18, 2018 at 00:39 UTC ( #1211167=note: print w/replies, xml ) Need Help??


in reply to Re^4: Hash key composition with a comma?
in thread Hash key composition with a comma?

I second you, cause it's very hard to construct a scenario where multi dim hashes cause a bug, even if the programmer was so naive to allow random keys.

And the statement:

> If your data contains the separator-character, the code breaks. 

Is not true. The constructed key would have more separator characters but wouldn't "break".

I'd really like to see a believable example, maybe I am missing something?

Cheers Rolf
(addicted to the Perl Programming Language and ☆☆☆☆ :)
Wikisyntax for the Monastery

  • Comment on Re^5: Hash key composition with a comma?

Replies are listed 'Best First'.
Re^6: Hash key composition with a comma?
by choroba (Bishop) on Mar 18, 2018 at 09:46 UTC
    Not sure if believable, but imagine
    my $k1a = "a$;b"; my $k1b = 'c'; my $k2a = 'a'; my $k2b = "b$;c"; $multi{$k1a, $k1b} = 1; $multi{$k2a, $k2b} = 2; print $multi{$k1a, $k1b}; # 2!!
    ($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord }map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
      Yes that's pretty much the example I came up with, only after thinking hard.

      "Karl-Heinz Urban" and "Karl Heinz-Urban" would get the same entry for $age{$first,$family} if $; was "-" and consequently a Hollywood actor would change age. (This never happens normally ;)

      But you first need to construct such a collision which results in data loss.

      Intuition (and AM) says "one injected delimiter and it breaks" like $b='x"y';eval qq {$a="$b"} breaks.

      But that's not the case, you need a coincidence where both keys are polluted in a very specific way.

      And a hash with polluted entries will continue to work normally as long as Mr "Heinz-Urban" doesn't show up.

      I'd like to see a more believable scenario.

      NB: Of course I wouldn't allow polluted keys in the first way.

      Cheers Rolf
      (addicted to the Perl Programming Language and ☆☆☆☆ :)
      Wikisyntax for the Monastery

      PS : AM is thanking you for doing his "homework"! ;)

      I haven't researched this, but a coworker just suggested to me that a credible cause of this in the wild might be some unicode pollution in input expected to be ascii.

      If she's right, perhaps it's not so far-fetched.

      -sauoq
      "My two cents aren't worth a dime.";
        I'm not sure about other encodings, but in UTF-8, all non-ASCII characters are represented by bytes > x7F, so x1c can't occur.
        ($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord }map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://1211167]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others scrutinizing the Monastery: (2)
As of 2019-09-23 03:04 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?
    The room is dark, and your next move is ...












    Results (276 votes). Check out past polls.

    Notices?