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
