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.
Now continuing in __nf_ct_ext_add() you do:
if (newlen >= ct->ext->real_len) {
^^^^^^^^
new = kmalloc(newlen, gfp);
if (!new)
return NULL;
So you're comparing newlen to the object size and not the buffer size
which is what you want and what ksize() and consequently my patch does.
Take a look at mm/util.c::krealloc(). It does exactly what you want
modulo the RCU bits. My patch converts the netfilter code to follow the
exact same semantics.
Pekka
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