Re: [RFC] [-mm] Remove 'unsafe' LZO decompressor

[Michael-Luke Jones <mlj28@cam.ac.uk>]

On 24 May 2007, at 19:50, Andrew Morton wrote:

> On Thu, 24 May 2007 18:15:17 +0100
> Michael-Luke Jones <mlj28@cam.ac.uk> wrote:
>
> > Attached is a patch which may be desirable for -mm. It applies
> > directly to 2.6.22-rc2-mm1.
> >
> > The patch removes the 'unsafe' LZO decompression function, lowering
> > the size of the minilzo.c file by nearly 500 out of an original 1727
> > lines. It also removes references to the 'unsafe' decompression
> > function in the public LZO header and the EXPORT_SYMBOL_GPL  
> > declaration.
> >
> > This is intended to provoke some discussion over whether a
> > decompression function able to scribble on arbitrary memory is
> > desirable in the mainline kernel, whatever the performance increases.
> >
> > Over and above the security/stability implications of using this
> > code, it can also be argued to represent an unnecessary duplication
> > of the vast majority of LZO decompression code. This is due to the
> > lack of likely in-kernel uses of the 'unsafe' function.
> >
> > Only a single user for this 'unsafe' code has been suggested, the
> > 'Compressed Caching' project. This code is highly unlikely to move
> > into mainline in the same timeframe as the LZO code. All of the other
> > suggested uses require decompression of untrusted data, such that the
> > 'safe' function should be used.
> >
> > Comments / disagreement all welcome :)
>
> This is obviously a highly desirable thing to do for a number of  
> reasons.
> But have we quantified the performance difference?

The author of LZO may be able to help us out here, so he's CCed as of  
this mail.

Michael-Luke

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