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 57555a4..e03d77d 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2018,7 +2018,10 @@
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 @@
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;