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

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Date:   Thu, 03 Nov 2016 17:36:06 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Dmitry Vyukov <dvyukov@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        netdev <netdev@...r.kernel.org>
CC:     LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: bpf: kernel BUG in htab_elem_free

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.

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);
  		}
  	}
  }