make zdb_decompress_block check its decompression reliably #15733
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This function decompresses to two buffers and then compares them to check whether the (opaque) decompression process filled the whole buffer. Previously it began with lbuf uninitialized and lbuf2 filled with pseudorandom data. This neither guarantees that any bytes not written by the compressor would be different, nor seems incredibly sound otherwise! After these changes, instead of filling one buffer with generated pseudorandom data we overwrite each buffer with completely different data. This should remove the possibility of low-probability failures, as well as make the process simpler and cheaper. Signed-off-by: Kent Ross <k@mad.cash>
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rincebrain
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Jan 9, 2024
lundman
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This function decompresses to two buffers and then compares them to check whether the (opaque) decompression process filled the whole buffer. Previously it began with lbuf uninitialized and lbuf2 filled with pseudorandom data. This neither guarantees that any bytes not written by the compressor would be different, nor seems incredibly sound otherwise! After these changes, instead of filling one buffer with generated pseudorandom data we overwrite each buffer with completely different data. This should remove the possibility of low-probability failures, as well as make the process simpler and cheaper. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Rich Ercolani <rincebrain@gmail.com> Signed-off-by: Kent Ross <k@mad.cash> Closes openzfs#15733
lundman
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Mar 13, 2024
This function decompresses to two buffers and then compares them to check whether the (opaque) decompression process filled the whole buffer. Previously it began with lbuf uninitialized and lbuf2 filled with pseudorandom data. This neither guarantees that any bytes not written by the compressor would be different, nor seems incredibly sound otherwise! After these changes, instead of filling one buffer with generated pseudorandom data we overwrite each buffer with completely different data. This should remove the possibility of low-probability failures, as well as make the process simpler and cheaper. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Rich Ercolani <rincebrain@gmail.com> Signed-off-by: Kent Ross <k@mad.cash> Closes openzfs#15733
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Motivation and Context
This function (
zdb_decompress_block) decompresses to two buffers and then compares them to check whether the (opaque) decompression process filled the whole buffer. Previously it began withlbufuninitialized andlbuf2filled with pseudorandom data. This neither guarantees that any bytes not written by the decompressor would be different, nor seems incredibly sound otherwise!After these changes, instead of filling one buffer with generated pseudorandom data we overwrite each buffer with completely different data. This should remove the possibility of low-probability failures, as well as make the process simpler and cheaper.
I noticed this while glancing over someone else's changes in the same function, and the possibility for some really niche and infuriating bugs here bothered me; this seems like a simple and straightforward improvement.
Description
How Has This Been Tested?
Types of changes
Checklist:
Signed-off-by.