ipsec: Fix pskb_expand_head corruption in xfrm_state_check_space

We're never supposed to shrink the headroom or tailroom.  In fact,
shrinking the headroom is a fatal action.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 4 deletions

diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c
index ac25b4c0e982..dc50f1e71f76 100644
--- a/net/xfrm/xfrm_output.c
+++ b/net/xfrm/xfrm_output.c
@@ -27,10 +27,14 @@ static int xfrm_state_check_space(struct xfrm_state *x, struct sk_buff *skb)
                 - skb_headroom(skb);
         int ntail = dst->dev->needed_tailroom - skb_tailroom(skb);
 
-        if (nhead > 0 || ntail > 0)
-                return pskb_expand_head(skb, nhead, ntail, GFP_ATOMIC);
-
-        return 0;
+        if (nhead <= 0) {
+                if (ntail <= 0)
+                        return 0;
+                nhead = 0;
+        } else if (ntail < 0)
+                ntail = 0;
+
+        return pskb_expand_head(skb, nhead, ntail, GFP_ATOMIC);
 }
 
 static int xfrm_output_one(struct sk_buff *skb, int err)