From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH] netlink: enable skb header refcounting before sending first broadcast Date: Fri, 10 Jul 2015 15:49:47 +0200 Message-ID: <1436536187.24939.50.camel@edumazet-glaptop2.roam.corp.google.com> References: <20150710115141.12980.88829.stgit@buzz> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, "David S. Miller" , Eric Dumazet , Herbert Xu To: Konstantin Khlebnikov Return-path: Received: from mail-wi0-f176.google.com ([209.85.212.176]:33800 "EHLO mail-wi0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754416AbbGJNtx (ORCPT ); Fri, 10 Jul 2015 09:49:53 -0400 Received: by wifm2 with SMTP id m2so47089200wif.1 for ; Fri, 10 Jul 2015 06:49:51 -0700 (PDT) In-Reply-To: <20150710115141.12980.88829.stgit@buzz> Sender: netdev-owner@vger.kernel.org List-ID: On Fri, 2015-07-10 at 14:51 +0300, Konstantin Khlebnikov wrote: > This fixes race between non-atomic updates of adjacent bit-fields: > skb->cloned could be lost because netlink broadcast clones skb after > sending it to the first listener who sets skb->peeked at the same skb. > As a result atomic refcounting of skb header stays disabled and > skb_release_data() frees it twice. Race leads to double-free in kmalloc-xxx. > > Signed-off-by: Konstantin Khlebnikov > Fixes: b19372273164 ("net: reorganize sk_buff for faster __copy_skb_header()") > --- > net/netlink/af_netlink.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c > index dea925388a5b..921e0d8dfe3a 100644 > --- a/net/netlink/af_netlink.c > +++ b/net/netlink/af_netlink.c > @@ -2028,6 +2028,12 @@ int netlink_broadcast_filtered(struct sock *ssk, struct sk_buff *skb, u32 portid > info.tx_filter = filter; > info.tx_data = filter_data; > > + /* Enable atomic refcounting in skb_release_data() before first send: > + * non-atomic set of that bit-field in __skb_clone() could race with > + * __skb_recv_datagram() which touches the same set of bit-fields. > + */ > + skb->cloned = 1; > + > /* While we sleep in clone, do not allow to change socket list */ > > netlink_lock_table(); Wow, this is tricky. I wonder how you found this bug ???? Acked-by: Eric Dumazet