[PATCH 3.16.y-ckt 81/94] ipv6: Fix IPsec pre-encap fragmentation check

[Luis Henriques]

3.16.7-ckt20 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>

commit 93efac3f2e03321129de67a3c0ba53048bb53e31 upstream.

The IPv6 IPsec pre-encap path performs fragmentation for tunnel-mode
packets.  That is, we perform fragmentation pre-encap rather than
post-encap.

A check was added later to ensure that proper MTU information is
passed back for locally generated traffic.  Unfortunately this
check was performed on all IPsec packets, including transport-mode
packets.

What's more, the check failed to take GSO into account.

The end result is that transport-mode GSO packets get dropped at
the check.

This patch fixes it by moving the tunnel mode check forward as well
as adding the GSO check.

Fixes: dd767856a36e ("xfrm6: Don't call icmpv6_send on local error")
Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
 net/ipv6/xfrm6_output.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/net/ipv6/xfrm6_output.c b/net/ipv6/xfrm6_output.c
index 433672d07d0b..0f8cd584cd3d 100644
--- a/net/ipv6/xfrm6_output.c
+++ b/net/ipv6/xfrm6_output.c
@@ -137,6 +137,7 @@ static int __xfrm6_output(struct sk_buff *skb)
 	struct dst_entry *dst = skb_dst(skb);
 	struct xfrm_state *x = dst->xfrm;
 	int mtu;
+	bool toobig;
 
 #ifdef CONFIG_NETFILTER
 	if (!x) {
@@ -145,24 +146,28 @@ static int __xfrm6_output(struct sk_buff *skb)
 	}
 #endif
 
+	if (x->props.mode != XFRM_MODE_TUNNEL)
+		goto skip_frag;
+
 	if (skb->protocol == htons(ETH_P_IPV6))
 		mtu = ip6_skb_dst_mtu(skb);
 	else
 		mtu = dst_mtu(skb_dst(skb));
 
-	if (skb->len > mtu && xfrm6_local_dontfrag(skb)) {
+	toobig = skb->len > mtu && !skb_is_gso(skb);
+
+	if (toobig && xfrm6_local_dontfrag(skb)) {
 		xfrm6_local_rxpmtu(skb, mtu);
 		return -EMSGSIZE;
-	} else if (!skb->ignore_df && skb->len > mtu && skb->sk) {
+	} else if (!skb->ignore_df && toobig && skb->sk) {
 		xfrm_local_error(skb, mtu);
 		return -EMSGSIZE;
 	}
 
-	if (x->props.mode == XFRM_MODE_TUNNEL &&
-	    ((skb->len > mtu && !skb_is_gso(skb)) ||
-		dst_allfrag(skb_dst(skb)))) {
+	if (toobig || dst_allfrag(skb_dst(skb)))
 			return ip6_fragment(skb, x->outer_mode->afinfo->output_finish);
-	}
+
+skip_frag:
 	return x->outer_mode->afinfo->output_finish(skb);
 }
 
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