Re: [RFC PATCH 2/3] add RWF_ENCODED for writing compressed data

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On 25 Sep 2019, at 8:07, Colin Walters wrote:

> On Wed, Sep 25, 2019, at 3:11 AM, Dave Chinner wrote:
>>
>> We're talking about user data read/write access here, not some
>> special security capability. Access to the data has already been
>> permission checked, so why should the format that the data is
>> supplied to the kernel in suddenly require new privilege checks?
>
> What happens with BTRFS today if userspace provides invalid compressed 
> data via this interface?  Does that show up as filesystem corruption 
> later?  If the data is verified at write time, wouldn't that be losing 
> most of the speed advantages of providing pre-compressed data?

The data is verified while being decompressed, but that's a fairly large 
fuzzing surface (all of zstd, zlib, and lzo).  A lot of people will 
correctly argue that we already have that fuzzing surface today, but I'd 
rather not make a really easy way to stuff arbitrary bytes through the 
kernel decompression code until all the projects involved sign off.

-chris




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