[Bug 789] gunzip/bunzip2/zcat output corrupted

bugzilla at busybox.net bugzilla at busybox.net
Fri Dec 11 09:51:29 UTC 2009


https://bugs.busybox.net/show_bug.cgi?id=789





--- Comment #2 from Michael McTernan <mmcternan at airvana.com>  2009-12-11 09:51:28 UTC ---
(In reply to comment #1)
> (In reply to comment #0)
> What is "sparse data"? File with holes? Can you attach data.gz which is
> producing errors when decompressed?

Apologies.  I tried to upload in the original report, but 400k is too large an
attachment for this Bugzilla.  I'm trying to find somewhere else to put the
data...  

The file itself is regular i.e. no holes,  The data has a lot of zeros in it
with occasional runs of data sequences.  It's 4Meg uncompressed, and compressed
to 400k - nice!

> > The output shows the following:
> > 
> >   58feaeb3349aeb1b97cef52ed454bc2c  -
> >   58feaeb3349aeb1b97cef52ed454bc2c  -
> >   58feaeb3349aeb1b97cef52ed454bc2c  -
> >   58feaeb3349aeb1b97cef52ed454bc2c  -
> >   58feaeb3349aeb1b97cef52ed454bc2c  -
> >   ...
> >   58feaeb3349aeb1b97cef52ed454bc2c  -
> > 
> > i.e. the corruption is always the same.
> 
> You contradict yourself. Is corruption always the same, or not?
> You effectively say "both" - ??!

The wrong hashes tend to take one of only a small set of values.  In the output
above the erroneous decompressions have always given the wrong hash of
58feaeb3349aeb1b97cef52ed454bc2c, but rerunning the test at a different time
may give a different wrong hash.

So the corruption is not always the same, but is far from random.  Examining
the good and bad decompression results also showed them to differ in only one
byte of the whole file.  

Aside, I tried building busybox on i686 Linux and running gunzip on the
troublesome file under Valgrind with the memchecker.  It was completely clean
or warnings/errors in that scenario, and also correctly compressed/decompressed
the data repeatedly.


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