From: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Date: Tue, 25 Nov 2008 21:57:01 +0000 (-0800)
Subject: tcp: skb_shift cannot cache frag ptrs past pskb_expand_head
X-Git-Tag: firefly_0821_release~16481^2~484
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=9f782db3f5ceee9aa8de6f853969fbec1b8c6e65;p=firefly-linux-kernel-4.4.55.git

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@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 57555a4525da..e03d77d4c1c9 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;