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SubjectRe: [PATCH] netfilter: replace horrible hack with ksize()
Pekka Enberg wrote:
> Hi Patrick,
>
> Patrick McHardy wrote:
>> > I think you are misunderstanding ksize() (see mm/slub.c::ksize() for
>> > example).
>>
>> The ksize() description in mm/slab.c matches exactly what netfilter
>> wants to do:
>
> Agreed.
>
> Patrick McHardy wrote:
>> The initial allocation size is calculated as max(size, min slab size)
>> and is stored as ext->alloc_size. When adding the first extension,
>
> Yes, this part is correct, however...
>
>> it allocates ext->alloc_size of memory and stores both the real amount
>> of space used (ext->len) and the actual size (ext->real_len).
>> When adding further extensions, it calculates the new total amount of
>> space needed (newlen). If that is larger than the real amount of
>> memory allocated (real_len), it reallocates.
>
> ...looking at nf_ct_ext_create() you do:
>
> *ext = kzalloc(real_len, gfp);
> ^^^^^^^^
> if (!*ext)
> return NULL;
>
> (*ext)->offset[id] = off;
> (*ext)->len = len;
> (*ext)->real_len = real_len;
> ^^^^^^^^
>
> You are storing the _object size_ (total amount of memory requested) and
> not the _buffer size_ (total amount of memory allocated). Keep in mind
> that object size < buffer size and that ksize() returns the latter.


For all length <= minimum slab size alloc_size (and thus
real_len) is equal to the buffer size. You are correct
however that your patch is fine, I somehow misread the

+ if (newlen >= ksize(ct->ext)) {

part and thought you would always compare against the
minimum slab size.

I've queued your patch and will pass it upstream after
some testing, thanks.


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