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Date:   Fri, 25 Nov 2022 09:46:04 +0000
From:   Giovanni Cabiddu <giovanni.cabiddu@intel.com>
To:     Herbert Xu <herbert@gondor.apana.org.au>
CC:     <linux-crypto@vger.kernel.org>, <qat-linux@intel.com>,
        Vlad Dronov <vdronov@redhat.com>
Subject: Re: [PATCH v2 11/11] crypto: qat - add resubmit logic for
 decompression
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On Fri, Nov 25, 2022 at 12:54:27PM +0800, Herbert Xu wrote:
> On Wed, Nov 23, 2022 at 12:10:32PM +0000, Giovanni Cabiddu wrote:
> >
> > +#define MAX_NULL_DST_RETRIES 5
> 
> Why do we need this limit?
I wanted a cap on the number of retries. What if the input is a zip
bomb [1]?

The alternative would be to retry up to the point the allocation of the
destination scatterlist fails.
What do you suggest?

> Doesn't that mean that anything that
> compresses by a factor of more than 2^5 or 2^6 will fail?
Anything that decompresses by more than (src size * 2 rounded up to 4K) * 2^6
will fail.

> Perhaps it would also be wise to enforce a minimum for dlen in
> case of a NULL dst, perhaps PAGE_SIZE just in case slen is very
> small and it would take many doublings to get to the right size.
This is done already. See this snippet from qat_comp_alg_compress_decompress():

	/* Handle acomp requests that require the allocation of a destination
	 * buffer. The size of the destination buffer is double the source
	 * buffer (rounded up to the size of a page) to fit the
	 * decompressed output or an expansion on the data for compression.
	 */
	if (!areq->dst) {
		qat_req->dst.is_null = true;

		dlen = round_up(2 * slen, PAGE_SIZE);
		areq->dst = sgl_alloc(dlen, f, NULL);

[1] https://en.wikipedia.org/wiki/Zip_bomb

Regards,

-- 
Giovanni