netdev - [PATCH] xfrm6: Fix ICMPv6 and MH header checks in _decode

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Date:	Fri, 11 Sep 2015 09:57:20 +0200
From:	Mathias Krause <minipli@...glemail.com>
To:	Steffen Klassert <steffen.klassert@...unet.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>
Cc:	Marcin Jurkowski <marcin1j@...il.com>, satmd@...n.at,
	netdev@...r.kernel.org, Mathias Krause <minipli@...glemail.com>,
	Mathias Krause <mathias.krause@...unet.com>,
	PaX Team <pageexec@...email.hu>
Subject: [PATCH] xfrm6: Fix ICMPv6 and MH header checks in _decode_session6

From: Mathias Krause <mathias.krause@...unet.com>

Ensure there's enough data left prior calling pskb_may_pull(). If
skb->data was already advanced, we'll call pskb_may_pull() with a
negative value converted to unsigned int -- leading to a huge
positive value. That won't matter in practice as pskb_may_pull()
will likely fail in this case, but it leads to underflow reports on
kernels handling such kind of over-/underflows, e.g. a PaX enabled
kernel instrumented with the size_overflow plugin.

Reported-by: satmd <satmd@...n.at>
Reported-and-tested-by: Marcin Jurkowski <marcin1j@...il.com>
Signed-off-by: Mathias Krause <mathias.krause@...unet.com>
Cc: PaX Team <pageexec@...email.hu>
---
 net/ipv6/xfrm6_policy.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/xfrm6_policy.c b/net/ipv6/xfrm6_policy.c
index ed0583c1b9fc..c988c3f033cf 100644
--- a/net/ipv6/xfrm6_policy.c
+++ b/net/ipv6/xfrm6_policy.c
@@ -174,7 +174,8 @@ _decode_session6(struct sk_buff *skb, struct flowi *fl, int reverse)
 			return;
 
 		case IPPROTO_ICMPV6:
-			if (!onlyproto && pskb_may_pull(skb, nh + offset + 2 - skb->data)) {
+			if (!onlyproto && (nh + offset + 2 < skb->data ||
+			    pskb_may_pull(skb, nh + offset + 2 - skb->data))) {
 				u8 *icmp;
 
 				nh = skb_network_header(skb);
@@ -188,7 +189,8 @@ _decode_session6(struct sk_buff *skb, struct flowi *fl, int reverse)
 #if IS_ENABLED(CONFIG_IPV6_MIP6)
 		case IPPROTO_MH:
 			offset += ipv6_optlen(exthdr);
-			if (!onlyproto && pskb_may_pull(skb, nh + offset + 3 - skb->data)) {
+			if (!onlyproto && (nh + offset + 3 < skb->data ||
+			    pskb_may_pull(skb, nh + offset + 3 - skb->data))) {
 				struct ip6_mh *mh;
 
 				nh = skb_network_header(skb);
-- 
2.1.4

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