From: Ken-ichirou MATSUZAWA <chamaken@gmail.com>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: David Miller <davem@davemloft.net>, netdev@vger.kernel.org, fw@strlen.de
Subject: Re: [PATCHv1 net-next 0/5] netlink: mmap: kernel panic and some issues
Date: Wed, 2 Sep 2015 09:04:00 +0900 [thread overview]
Message-ID: <20150902000400.GA14821@gmail.com> (raw)
In-Reply-To: <55D492CC.6010602@iogearbox.net>
On Wed, Aug 19, 2015 at 04:29:32PM +0200, Daniel Borkmann wrote:
> On 08/17/2015 11:02 PM, David Miller wrote:
> >From: Daniel Borkmann <daniel@iogearbox.net>
> >Date: Fri, 14 Aug 2015 12:38:21 +0200
> >
> >>diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
> >>index 67d2104..4307446 100644
> >>--- a/net/netlink/af_netlink.c
> >>+++ b/net/netlink/af_netlink.c
> >>@@ -238,6 +238,13 @@ static void __netlink_deliver_tap(struct sk_buff
> >>*skb)
> >>
> >> static void netlink_deliver_tap(struct sk_buff *skb)
> >> {
> >>+ /* Netlink mmaped skbs must not access shared info, and thus
> >>+ * are not allowed to be cloned. For now, just don't allow
> >>+ * them to get inspected by taps.
> >>+ */
> >>+ if (netlink_skb_is_mmaped(skb))
> >>+ return;
> >>+
> >
> >I would seriously rather see us do an expensive full copy of the SKB
> >than to have traffic which is unexpectedly invisible to taps.
>
> Do you mean generically as we do in TX path, or only in this
> particular scenario?
It seems that we only handle this particular scenario.
I think I can understand the cause of the panic. The original mmaped
skb, allocated by netlink_alloc_skb, has a skb destructor which set
skb head NULL. This prevents from accessing shared info in
skb_release_all, so my concerns that the shared info of original skb
may be accessed in kfree_skb and may cause a panic, is unnecessary.
But since skb_clone does not copy the destructor, skb_release_all
calls skb_release_data for cloned skb, accessing shared info and
causes the panic, I think. Setting the destructor after clone could
not fix the problem since __dev_queue_xmit call path,
netif_skb_features?, accesses shared info.
Talking about skb_copy path, original skb's shared info is accessed
only in copy_skb_header, to get gso related field. As a result of
those, we can avoid the panic by:
@@ -205,7 +205,10 @@ static int __netlink_deliver_tap_skb(struct sk_buff *skb,
int ret = -ENOMEM;
dev_hold(dev);
- nskb = skb_clone(skb, GFP_ATOMIC);
+ if (netlink_skb_is_mmaped(skb))
+ nskb = skb_copy(skb, GFP_ATOMIC);
+ else
+ nskb = skb_clone(skb, GFP_ATOMIC);
Thanks to you, my question become clear:
Should we set gso_size to 0 after copying to make skb_is_gso
returning false?
Thanks,
next prev parent reply other threads:[~2015-09-02 0:04 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-22 13:17 [RFC PATCH 0/5] netlink: mmap kernel panic and some issues Ken-ichirou MATSUZAWA
2015-08-12 8:28 ` [PATCHv1 net-next 0/5] netlink: mmap: " Ken-ichirou MATSUZAWA
2015-08-12 8:31 ` [PATCHv1 net-next 1/5] netlink: mmap: introduce mmaped skb helper functions Ken-ichirou MATSUZAWA
2015-08-12 8:32 ` [PATCHv1 net-next 2/5] netlink: mmap: apply " Ken-ichirou MATSUZAWA
2015-08-12 8:34 ` [PATCHv1 net-next 3/5] netlink: mmap: fix status for not delivered skb Ken-ichirou MATSUZAWA
2015-08-12 8:35 ` [PATCHv1 net-next 4/5] netlink: mmap: update tx type check Ken-ichirou MATSUZAWA
2015-08-12 8:38 ` [PATCHv1 net-next 5/5] netlink: mmap: notify only when NL_MMAP_STATUS_VALID frame exists Ken-ichirou MATSUZAWA
2015-08-12 23:38 ` [PATCHv1 net-next 0/5] netlink: mmap: kernel panic and some issues David Miller
2015-08-14 8:58 ` Ken-ichirou MATSUZAWA
2015-08-14 10:01 ` Daniel Borkmann
2015-08-14 10:38 ` Daniel Borkmann
2015-08-15 2:25 ` Ken-ichirou MATSUZAWA
2015-08-17 21:02 ` David Miller
2015-08-19 14:29 ` Daniel Borkmann
2015-09-02 0:04 ` Ken-ichirou MATSUZAWA [this message]
2015-09-02 9:47 ` Daniel Borkmann
2015-09-02 11:35 ` Ken-ichirou MATSUZAWA
2015-09-02 15:56 ` Daniel Borkmann
2015-09-02 22:27 ` Ken-ichirou MATSUZAWA
2015-09-07 14:54 ` Daniel Borkmann
2015-09-09 5:59 ` David Miller
2015-09-09 8:53 ` Thomas Graf
2015-09-09 9:22 ` Daniel Borkmann
2015-08-20 3:43 ` [PATCH net] netlink: mmap: fix tx type check Ken-ichirou MATSUZAWA
2015-08-23 23:06 ` David Miller
2015-08-20 5:54 ` [PATCH net] netlink: rx mmap: fix POLLIN condition Ken-ichirou MATSUZAWA
2015-08-26 3:17 ` David Miller
2015-08-28 7:00 ` Ken-ichirou MATSUZAWA
2015-08-28 7:05 ` [PATCH net] netlink: mmap: fix lookup frame position Ken-ichirou MATSUZAWA
2015-08-29 5:26 ` David Miller
2015-08-30 22:54 ` [PATCH net] netlink: rx mmap: fix POLLIN condition Ken-ichirou MATSUZAWA
2015-08-31 4:56 ` David Miller
2015-08-20 7:07 ` [PATCH net] netlink: mmap: fix status setting in skb destructor Ken-ichirou MATSUZAWA
2015-08-26 3:22 ` David Miller
2015-08-28 7:37 ` Ken-ichirou MATSUZAWA
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