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SubjectRe: slab corruption with current -git (was Re: [git pull] vfs pile 1 (splice))
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Florian Westphal <fw@strlen.de> writes:

> Linus Torvalds <torvalds@linux-foundation.org> wrote:
>> On Sun, Oct 9, 2016 at 12:11 PM, Linus Torvalds
>> <torvalds@linux-foundation.org> wrote:
>> >
>> > Anyway, I don't think I can bisect it, but I'll try to narrow it down
>> > a *bit* at least.
>> >
>> > Not doing any more pulls on this unstable base, I've been puttering
>> > around in trying to clean up some stupid printk logging issues
>> > instead.
>>
>> So I finally got a oops with slub debugging enabled. It doesn't really
>> narrow things down, though, it kind of extends on the possible
>> suspects. Now adding David Miller and Pablo, because it looks like it
>> may be netfilter that does something bad and corrupts memory.
>
> Quite possible, the netns interactions are not nice :-/
>
>> Without further ado, here's the new oops:
>>
>> general protection fault: 0000 [#1] SMP
>> CPU: 7 PID: 169 Comm: kworker/u16:7 Not tainted
>> 4.8.0-11288-gb66484cd7470 #1
>> Hardware name: System manufacturer System Product Name/Z170-K, BIOS
> ..
>> Call Trace:
>> netfilter_net_exit+0x2f/0x60
>> ops_exit_list.isra.4+0x38/0x60
>> cleanup_net+0x1ba/0x2a0
>> process_one_work+0x1f1/0x480
>> worker_thread+0x48/0x4d0
>> ? process_one_work+0x480/0x480
>
> ..
>
>> like it's a pointer loaded from a free'd allocation.
>>
>> The code disassembles to
>>
>> 0: 0f b6 ca movzbl %dl,%ecx
>> 3: 48 8d 84 c8 00 01 00 lea 0x100(%rax,%rcx,8),%rax
>> a: 00
>> b: 49 8b 5c c5 00 mov 0x0(%r13,%rax,8),%rbx
>> 10: 48 85 db test %rbx,%rbx
>> 13: 0f 84 cb 00 00 00 je 0xe4
>> 19: 4c 3b 63 40 cmp 0x40(%rbx),%r12
>> 1d: 48 8b 03 mov (%rbx),%rax
>> 20: 0f 84 e9 00 00 00 je 0x10f
>> 26: 48 85 c0 test %rax,%rax
>> 29: 74 26 je 0x51
>> 2b:* 4c 3b 60 40 cmp 0x40(%rax),%r12 <-- trapping instruction
>> 2f: 75 08 jne 0x39
>> 31: e9 ef 00 00 00 jmpq 0x125
>> 36: 48 89 d8 mov %rbx,%rax
>> 39: 48 8b 18 mov (%rax),%rbx
>> 3c: 48 85 db test %rbx,%rbx
>>
>> and that oopsing instruction seems to be the compare of
>> "hooks_entry->orig_ops" from hooks_entry in this expression:
>>
>> if (hooks_entry && hooks_entry->orig_ops == reg) {
>>
>> so hooks_entry() is bogus. It was gotten from
>>
>> hooks_entry = nf_hook_entry_head(net, reg);
>>
>> but that's as far as I dug. And yes, I do have
>> CONFIG_NETFILTER_INGRESS=y in case that matters.
>>
>> And all this code has changed pretty radically in commit e3b37f11e6e4
>> ("netfilter: replace list_head with single linked list"), and there
>> was clearly already something wrong with that code, with commit
>> 5119e4381a90 ("netfilter: Fix potential null pointer dereference")
>> adding the test against NULL. But I suspect that only hid the "oops,
>> it's actually not NULL, it loaded some uninitialized value" problem.
>>
>> Over to the networking guys.. Ideas?
>
> Sorry, not off the top of my head.
> Pablo is currently travelling back home from netdev 1.2 in Tokyo,
> I can help starting Wednesday when I am back.
>
> One shot in the dark (not even compile tested; wonder if we can end up
> zapping bogus hook ...)
>

I was just about to build and test something similar:

diff --git a/net/netfilter/core.c b/net/netfilter/core.c
index c9d90eb..e84103f 100644
--- a/net/netfilter/core.c
+++ b/net/netfilter/core.c
@@ -189,7 +189,7 @@ void nf_unregister_net_hook(struct net *net, const struct nf_hook_ops *reg)

unlock:
mutex_unlock(&nf_hook_mutex);
- if (!hooks_entry) {
+ if (!hooks_entry || hooks_entry->orig_ops != reg) {
WARN(1, "nf_unregister_net_hook: hook not found!\n");
return;
}
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