commit 9d7ceb18f628bd6ad67c1dc1355f907e0ca714f6
author Eric Dumazet <edumazet@google.com> Sat Feb 04 23:18:55 2017 -0800
committer Mark Salyzyn <salyzyn@google.com> Mon Jun 12 08:34:51 2017 -0700
tree 8b27a97b3cd6f554dd2208efd6800e4ebd2f045a
parent 6fe4b76beddd115aea5e11db3c7ea713b800b444

BACKPORT: ip6_gre: fix ip6gre_err() invalid reads

Andrey Konovalov reported out of bound accesses in ip6gre_err()

If GRE flags contains GRE_KEY, the following expression
*(((__be32 *)p) + (grehlen / 4) - 1)

accesses data ~40 bytes after the expected point, since
grehlen includes the size of IPv6 headers.

Let's use a "struct gre_base_hdr *greh" pointer to make this
code more readable.

p[1] becomes greh->protocol.
grhlen is the GRE header length.

Fixes: c12b395a4664 ("gre: Support GRE over IPv6")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Roberto Pereira <rpere@google.com>
(cherry picked from commit 7892032cfe67f4bde6fc2ee967e45a8fbaf33756)
Bug:37871211
Change-Id: I839afd0948805b98e1aa6cbaca56f2e443f303af

net/ipv6/ip6_gre.c

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 7eb7267..0a7c371 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -365,35 +365,37 @@
 
 
 static void ip6gre_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
-		u8 type, u8 code, int offset, __be32 info)
+		       u8 type, u8 code, int offset, __be32 info)
 {
-	const struct ipv6hdr *ipv6h = (const struct ipv6hdr *)skb->data;
-	__be16 *p = (__be16 *)(skb->data + offset);
-	int grehlen = offset + 4;
+	const struct gre_base_hdr *greh;
+	const struct ipv6hdr *ipv6h;
+	int grehlen = sizeof(*greh);
 	struct ip6_tnl *t;
+	int key_off = 0;
 	__be16 flags;
+	__be32 key;
 
-	flags = p[0];
-	if (flags&(GRE_CSUM|GRE_KEY|GRE_SEQ|GRE_ROUTING|GRE_VERSION)) {
-		if (flags&(GRE_VERSION|GRE_ROUTING))
-			return;
-		if (flags&GRE_KEY) {
-			grehlen += 4;
-			if (flags&GRE_CSUM)
-				grehlen += 4;
-		}
+	if (!pskb_may_pull(skb, offset + grehlen))
+		return;
+	greh = (const struct gre_base_hdr *)(skb->data + offset);
+	flags = greh->flags;
+	if (flags & (GRE_VERSION | GRE_ROUTING))
+		return;
+	if (flags & GRE_CSUM)
+		grehlen += 4;
+	if (flags & GRE_KEY) {
+		key_off = grehlen + offset;
+		grehlen += 4;
 	}
 
-	/* If only 8 bytes returned, keyed message will be dropped here */
-	if (!pskb_may_pull(skb, grehlen))
+	if (!pskb_may_pull(skb, offset + grehlen))
 		return;
 	ipv6h = (const struct ipv6hdr *)skb->data;
-	p = (__be16 *)(skb->data + offset);
+	greh = (const struct gre_base_hdr *)(skb->data + offset);
+	key = key_off ? *(__be32 *)(skb->data + key_off) : 0;
 
 	t = ip6gre_tunnel_lookup(skb->dev, &ipv6h->daddr, &ipv6h->saddr,
-				flags & GRE_KEY ?
-				*(((__be32 *)p) + (grehlen / 4) - 1) : 0,
-				p[1]);
+				 key, greh->protocol);
 	if (t == NULL)
 		return;