Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, Oct 12, 2016 at 11:27 PM, Markus Trippelsdorf
> <markus@xxxxxxxxxxxxxxx> wrote:
> >
> > Yeah.
> >
> > 105 entry->orig_ops = reg;
> > 106 entry->ops = *reg;
> > 107 entry->next = NULL;
>
> So ipt_register_table() does:
>
> ret = nf_register_net_hooks(net, ops, hweight32(table->valid_hooks));
>
> and then nf_register_net_hooks() just does
>
> for (i = 0; i < n; i++) {
> err = nf_register_net_hook(net, ®[i]);
>
> so if the *reg is uninitialized, it means that it's the 'ops[]' array
> that isn't actually really valid in "valid_hooks". Odd. They should
> all be initialized by xt_hook_ops_alloc(), no?
Its only partially initialized. Looking at Markus' splat
its complaining about first 16 bytes (list_head), whose contents are indeed
undefined when it gets copied to entry->ops.
For the time being this seems like the most simple "fix", until we
disentangle the hook description (which should be const) from run-time
allocated data.
diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index e0aa7c1d0224..fc4977456c30 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -1513,7 +1513,7 @@ xt_hook_ops_alloc(const struct xt_table *table,
nf_hookfn *fn)
if (!num_hooks)
return ERR_PTR(-EINVAL);
- ops = kmalloc(sizeof(*ops) * num_hooks, GFP_KERNEL);
+ ops = kcalloc(num_hooks, sizeof(*ops), GFP_KERNEL);
if (ops == NULL)
return ERR_PTR(-ENOMEM);
I'll pass such a patch to Pablo.
> That said, xt_hook_ops_alloc() itself is odd. Lookie here, this is the
> loop that initializes things:
>
> for (i = 0, hooknum = 0; i < num_hooks && hook_mask != 0;
> hook_mask >>= 1, ++hooknum) {
>
> and it makes no sense to me how that tests *both* "i < num_hools" and
> "hook_mask != 0".
Right, one of these is enough.
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