linux-kernel - Re: bpf: kernel BUG in htab_elem

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Message-ID: <CACT4Y+b2CrmxEiL5XmKxPTXBjeYRcFbq7NapnAbuet+_NJBU_A@mail.gmail.com>
Date:   Thu, 3 Nov 2016 18:43:35 -0600
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: bpf: kernel BUG in htab_elem_free

On Thu, Nov 3, 2016 at 10:36 AM, Daniel Borkmann <daniel@...earbox.net> wrote:
> On 11/03/2016 03:15 PM, Dmitry Vyukov wrote:
>>
>> On Wed, Nov 2, 2016 at 11:14 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>>>
>>> Here we go.
>>>
>>> The following program triggers kernel BUG in htab_elem_free.
>>> On commit 0c183d92b20b5c84ca655b45ef57b3318b83eb9e (Oct 31).
>>> Run as "while true; do ./a.out; done".
>
>
> This one fixes it for me. Could you check it from your side as well?
> I'll submit an official fix then.

I've seen you mailed the fix already.
If you were able to reproduce it and test the fix, then there is
nothing else I can do.

> Thanks a lot for the catch!
> Daniel
>
> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
> index 570eeca..ad1bc67 100644
> --- a/kernel/bpf/hashtab.c
> +++ b/kernel/bpf/hashtab.c
> @@ -687,7 +687,8 @@ static void delete_all_elements(struct bpf_htab *htab)
>
>                 hlist_for_each_entry_safe(l, n, head, hash_node) {
>                         hlist_del_rcu(&l->hash_node);
> -                       htab_elem_free(htab, l);
> +                       if (l->state != HTAB_EXTRA_ELEM_USED)
> +                               htab_elem_free(htab, l);
>                 }
>         }
>  }