Re: slab corruption with current -git

From: Linus Torvalds
Date: Thu Oct 13 2016 - 15:52:52 EST

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, &reg[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?

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".

Why? Because

num_hooks = hweight32(hook_mask);

so it's entirely redundant. num_hooks is already how many bits are on
in hook_mask, so that test is just duplicating the same thing twice
("have we done less than that number of bits" and "do we have any bits

I don't know. There's something odd going on. Regardless, thsi is a
different problem from the nf_register_net_hook() list handling, so
I'll leave it to the networking people. David?