netdev - [PATCH] tcp: skb_shift cannot cache frag ptrs past pskb_expand

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Message-ID: <Pine.LNX.4.64.0811252202550.14851@wrl-59.cs.helsinki.fi>
Date:	Tue, 25 Nov 2008 22:08:06 +0200 (EET)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	David Miller <davem@...emloft.net>
cc:	Netdev <netdev@...r.kernel.org>
Subject: [PATCH] tcp: skb_shift cannot cache frag ptrs past pskb_expand_head


Since pskb_expand_head creates copy of the shared area we
cannot keep any frag ptr past de-cloning. This fixes the
tcpdump recvfrom -EFAULT problem.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
---
 net/core/skbuff.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 57555a4..133ecd6 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2018,7 +2018,10 @@ void skb_split(struct sk_buff *skb, struct sk_buff *skb1, const u32 len)
 		skb_split_no_header(skb, skb1, len, pos);
 }
 
-/* Shifting from/to a cloned skb is a no-go. */
+/* Shifting from/to a cloned skb is a no-go.
+ *
+ * Caller cannot keep skb_shinfo related pointers past calling here!
+ */
 static int skb_prepare_for_shift(struct sk_buff *skb)
 {
 	return skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC);
@@ -2070,6 +2073,8 @@ int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen)
 			    skb_prepare_for_shift(tgt))
 				return 0;
 
+			/* All previous frag pointers might be stale! */
+			fragfrom = &skb_shinfo(skb)->frags[from];
 			fragto = &skb_shinfo(tgt)->frags[merge];
 
 			fragto->size += shiftlen;
-- 
1.5.6.5