Messages in this thread | | | Date | Thu, 06 Mar 2008 17:49:11 +0200 | From | Pekka Enberg <> | Subject | Re: [PATCH] netfilter: replace horrible hack with ksize() |
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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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