From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Berg Subject: Re: [PATCH net-next-2.6] netlink: netlink_recvmsg() fix Date: Wed, 21 Jul 2010 10:05:29 +0200 Message-ID: <1279699529.3707.5.camel@jlt3.sipsolutions.net> References: <1279631789.2498.71.camel@edumazet-laptop> <1279639232.2498.82.camel@edumazet-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: David Miller , netdev To: Eric Dumazet Return-path: Received: from he.sipsolutions.net ([78.46.109.217]:57535 "EHLO sipsolutions.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762740Ab0GUIFd (ORCPT ); Wed, 21 Jul 2010 04:05:33 -0400 In-Reply-To: <1279639232.2498.82.camel@edumazet-laptop> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, 2010-07-20 at 17:20 +0200, Eric Dumazet wrote: > [PATCH net-next-2.6 v2] netlink: netlink_recvmsg() fix > > commit 1dacc76d0014 > (net/compat/wext: send different messages to compat tasks) > introduced a race condition on netlink, in case MSG_PEEK is used. > > An skb given by skb_recv_datagram() might be shared, we must copy it > before any modification, or risk fatal corruption. Makes sense to me, seeing that if you MSG_PEEK it just increases skb->users. But nothing could touch the other skb at the same time? Although I guess with netlink multicast we have a similar situation. johannes > Signed-off-by: Eric Dumazet > --- > net/netlink/af_netlink.c | 13 +++++++------ > 1 file changed, 7 insertions(+), 6 deletions(-) > > diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c > index 7aeaa83..1537fa5 100644 > --- a/net/netlink/af_netlink.c > +++ b/net/netlink/af_netlink.c > @@ -1405,7 +1405,7 @@ static int netlink_recvmsg(struct kiocb *kiocb, struct socket *sock, > struct netlink_sock *nlk = nlk_sk(sk); > int noblock = flags&MSG_DONTWAIT; > size_t copied; > - struct sk_buff *skb, *frag __maybe_unused = NULL; > + struct sk_buff *skb; > int err; > > if (flags&MSG_OOB) > @@ -1440,7 +1440,12 @@ static int netlink_recvmsg(struct kiocb *kiocb, struct socket *sock, > kfree_skb(skb); > skb = compskb; > } else { > - frag = skb_shinfo(skb)->frag_list; > + skb = skb_unshare(skb, GFP_KERNEL); > + if (!skb) { > + err = -ENOMEM; > + goto out; > + } > + kfree_skb(skb_shinfo(skb)->frag_list); > skb_shinfo(skb)->frag_list = NULL; > } > } > @@ -1477,10 +1482,6 @@ static int netlink_recvmsg(struct kiocb *kiocb, struct socket *sock, > if (flags & MSG_TRUNC) > copied = skb->len; > > -#ifdef CONFIG_COMPAT_NETLINK_MESSAGES > - skb_shinfo(skb)->frag_list = frag; > -#endif > - > skb_free_datagram(sk, skb); > > if (nlk->cb && atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf / 2) > > >