linux-kernel - [PATCH 4.4 026/342] flow_dissector: Fix unaligned access in __skb_flow_dissector when used by eth_get

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Message-Id: <20160301234528.830818388@linuxfoundation.org>
Date:	Tue, 01 Mar 2016 23:53:52 +0000
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	<linux-kernel@...r.kernel.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<stable@...r.kernel.org>,
	Sowmini Varadhan <sowmini.varadhan@...cle.com>,
	Alexander Duyck <aduyck@...antis.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.4 026/342] flow_dissector: Fix unaligned access in __skb_flow_dissector when used by eth_get_headlen

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

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

From: Alexander Duyck <aduyck@...antis.com>

[ Upstream commit 461547f3158978c180d74484d58e82be9b8e7357 ]

This patch fixes an issue with unaligned accesses when using
eth_get_headlen on a page that was DMA aligned instead of being IP aligned.
The fact is when trying to check the length we don't need to be looking at
the flow label so we can reorder the checks to first check if we are
supposed to gather the flow label and then make the call to actually get
it.

v2:  Updated path so that either STOP_AT_FLOW_LABEL or KEY_FLOW_LABEL can
     cause us to check for the flow label.

Reported-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>
Signed-off-by: Alexander Duyck <aduyck@...antis.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/core/flow_dissector.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -208,7 +208,6 @@ ip:
 	case htons(ETH_P_IPV6): {
 		const struct ipv6hdr *iph;
 		struct ipv6hdr _iph;
-		__be32 flow_label;
 
 ipv6:
 		iph = __skb_header_pointer(skb, nhoff, sizeof(_iph), data, hlen, &_iph);
@@ -230,8 +229,12 @@ ipv6:
 			key_control->addr_type = FLOW_DISSECTOR_KEY_IPV6_ADDRS;
 		}
 
-		flow_label = ip6_flowlabel(iph);
-		if (flow_label) {
+		if ((dissector_uses_key(flow_dissector,
+					FLOW_DISSECTOR_KEY_FLOW_LABEL) ||
+		     (flags & FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL)) &&
+		    ip6_flowlabel(iph)) {
+			__be32 flow_label = ip6_flowlabel(iph);
+
 			if (dissector_uses_key(flow_dissector,
 					       FLOW_DISSECTOR_KEY_FLOW_LABEL)) {
 				key_tags = skb_flow_dissector_target(flow_dissector,