netdev - [PATCH 2/2 v2] xfrm6: fix a potential use after free in xfrm6

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Message-Id: <1413968993-13528-2-git-send-email-roy.qing.li@gmail.com>
Date:	Wed, 22 Oct 2014 17:09:53 +0800
From:	roy.qing.li@...il.com
To:	netdev@...r.kernel.org
Subject: [PATCH 2/2 v2] xfrm6: fix a potential use after free in xfrm6_policy.c

From: Li RongQing <roy.qing.li@...il.com>

pskb_may_pull() maybe change skb->data and make nh and exthdr pointer
oboslete, so recompute the nd and exthdr

Signed-off-by: Li RongQing <roy.qing.li@...il.com>
---
Diff v1: add space between the date type and *, like (__be16 *)

 net/ipv6/xfrm6_policy.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/xfrm6_policy.c b/net/ipv6/xfrm6_policy.c
index ac49f84..5f98364 100644
--- a/net/ipv6/xfrm6_policy.c
+++ b/net/ipv6/xfrm6_policy.c
@@ -170,8 +170,10 @@ _decode_session6(struct sk_buff *skb, struct flowi *fl, int reverse)
 		case IPPROTO_DCCP:
 			if (!onlyproto && (nh + offset + 4 < skb->data ||
 			     pskb_may_pull(skb, nh + offset + 4 - skb->data))) {
-				__be16 *ports = (__be16 *)exthdr;
+				__be16 *ports;
 
+				nh = skb_network_header(skb);
+				ports = (__be16 *)(nh + offset);
 				fl6->fl6_sport = ports[!!reverse];
 				fl6->fl6_dport = ports[!reverse];
 			}
@@ -180,8 +182,10 @@ _decode_session6(struct sk_buff *skb, struct flowi *fl, int reverse)
 
 		case IPPROTO_ICMPV6:
 			if (!onlyproto && pskb_may_pull(skb, nh + offset + 2 - skb->data)) {
-				u8 *icmp = (u8 *)exthdr;
+				u8 *icmp;
 
+				nh = skb_network_header(skb);
+				icmp = (u8 *)(nh + offset);
 				fl6->fl6_icmp_type = icmp[0];
 				fl6->fl6_icmp_code = icmp[1];
 			}
@@ -192,8 +196,9 @@ _decode_session6(struct sk_buff *skb, struct flowi *fl, int reverse)
 		case IPPROTO_MH:
 			if (!onlyproto && pskb_may_pull(skb, nh + offset + 3 - skb->data)) {
 				struct ip6_mh *mh;
-				mh = (struct ip6_mh *)exthdr;
 
+				nh = skb_network_header(skb);
+				mh = (struct ip6_mh *)(nh + offset);
 				fl6->fl6_mh_type = mh->ip6mh_type;
 			}
 			fl6->flowi6_proto = nexthdr;
-- 
1.7.10.4

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