On Sun, May 01, 2016 at 09:48:34PM +0200, Florian Westphal wrote: > Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> wrote: > > [ Sorry for late reply ] > > > On Sun, Apr 24, 2016 at 01:18:21AM +0200, Florian Westphal wrote: > > > Can overflow so we might allocate very small table when bucket count is > > > high on a 32bit platform. > > > > > > Note: resize is only possible from init_netns. > > > > > > Signed-off-by: Florian Westphal <fw@xxxxxxxxx> > > > --- > > > net/netfilter/nf_conntrack_core.c | 7 +++++++ > > > 1 file changed, 7 insertions(+) > > > > > > diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c > > > index 2bbb962..11daca5 100644 > > > --- a/net/netfilter/nf_conntrack_core.c > > > +++ b/net/netfilter/nf_conntrack_core.c > > > @@ -1563,8 +1563,15 @@ void *nf_ct_alloc_hashtable(unsigned int *sizep, int nulls) > > > unsigned int nr_slots, i; > > > size_t sz; > > > > > > + if (*sizep > (UINT_MAX / sizeof(struct hlist_nulls_head))) > > > + return NULL; > > > > *sizep gets initially set to the number of buckets. > > Yes. > > > > BUILD_BUG_ON(sizeof(struct hlist_nulls_head) != sizeof(struct hlist_head)); > > > nr_slots = *sizep = roundup(*sizep, PAGE_SIZE / sizeof(struct hlist_nulls_head)); > > > > Then, this value is divided by the number of hlist heads that fit into > > a page. > > No, its rounded up to a multiple of PAGE/hlist heads, so for very large > values of *sizep nr_slots would be 0. > > > > + if (nr_slots > (UINT_MAX / sizeof(struct hlist_nulls_head))) > > > + return NULL; > > Alternative would be to change this to: > > if (nr_slots == 0 || nr_slots > (UINT_MAX / sizeof(struct hlist_nulls_head))) > return NULL; > > Or, add this check: > > if (nr_slots < roundup(1, PAGE_SIZE / sizeof(struct hlist_nulls_head)) > nr_slots = roundup(1, PAGE_SIZE / sizeof(struct hlist_nulls_head))) > > I wasn't sure if its better to fail or if we should just pretend a sane > value was given. I prefer an explicit failure, so the user knows that what is asking for is not supported, rather than masking the problem. > Let me know what you think and I'll submit a v2. > > [ Its not a big deal, but eventually I'd like to make the sysctl > writeable so users can just increase that, no need to use this obscure > module parameter/sysfs param ... ] Sounds good to me. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
