netdev - [PATCH 3.2-3.12] skbuff: skb_segment: orphan frags before copying

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Date:	Fri, 06 Jun 2014 17:09:28 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	David Miller <davem@...emloft.net>, stable <stable@...r.kernel.org>
Cc:	netdev <netdev@...r.kernel.org>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Herbert Xu <herbert@...dor.apana.org.au>
Subject: [PATCH 3.2-3.12] skbuff: skb_segment: orphan frags before copying

From: "Michael S. Tsirkin" <mst@...hat.com>

commit 1fd819ecb90cc9b822cd84d3056ddba315d3340f upstream.

skb_segment copies frags around, so we need
to copy them carefully to avoid accessing
user memory after reporting completion to userspace
through a callback.

skb_segment doesn't normally happen on datapath:
TSO needs to be disabled - so disabling zero copy
in this case does not look like a big deal.

Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
Acked-by: Herbert Xu <herbert@...dor.apana.org.au>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.2.  As skb_segment() only supports page-frags *or* a
 frag list, there is no need for the additional frag_skb pointer or the
 preparatory renaming.]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
This is what I used in Debian for 3.2, and I believe it applies to all
stable branches up to 3.12 inclusive.

For branches older than 3.6, this requires cherry-picking commit
a353e0ce0fd4 ('skbuff: add an api to orphan frags').  To avoid breaking
OOT builds of openvswitch, which will use skb_orphan_frags() if
available, it is also necessary to cherry-pick commit dcc0fb782b3a
('skbuff: export skb_copy_ubufs').

Ben.

--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2701,6 +2701,9 @@ struct sk_buff *skb_segment(struct sk_bu
 						 skb_put(nskb, hsize), hsize);

 		while (pos < offset + len && i < nfrags) {
+			if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC)))
+				goto err;
+
 			*frag = skb_shinfo(skb)->frags[i];
 			__skb_frag_ref(frag);
 			size = skb_frag_size(frag);

-- 
Ben Hutchings
You can't have everything.  Where would you put it?

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