Bug#703240: apt: pkgTagSection.Exists sometimes lies about a field being present, .Find does not

[Julian Andres Klode <jak@debian.org>]

On Sun, Mar 17, 2013 at 03:26:33PM +0100, Niels Thykier wrote:
> Package: apt
> Version: 0.9.7.8
> Severity: normal
> 
> Hi,
> 
> There is a flaw in the handling of hash collisions in pkgTagSection's
> "Exists" method that makes the "Exists" method return true even if the
> "Tag" (field) is not present.
> 
> This is visible already in the header file, tagfile.h:
> 
>  """
>    /* This very simple hash function for the last 8 letters gives
>       very good performance on the debian package files */
>    inline static unsigned long AlphaHash(const char *Text, const char *End = 0)
>    [...]
> 
>    inline bool Exists(const char* const Tag) {return AlphaIndexes[AlphaHash(Tag)] != 0;}
> """

And unfortunately, this is inline code, so if we wanted to really
fix this, we need a rebuild of the reverse dependencies, as they
won't pick up the fixed code otherwise. I propose making this 
non-inline when this gets fixed.

-- 
Julian Andres Klode  - Debian Developer, Ubuntu Member

See http://wiki.debian.org/JulianAndresKlode and http://jak-linux.org/.