Commit 7892032c authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

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: c12b395a ("gre: Support GRE over IPv6")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reported-by: default avatarAndrey Konovalov <andreyknvl@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent d71b7896

net/ipv6/ip6_gre.c

+21 −19
Original line number Diff line number Diff line
@@ -369,33 +369,35 @@ static void ip6gre_tunnel_uninit(struct net_device *dev) 
static void ip6gre_err(struct sk_buff *skb, struct inet6_skb_parm *opt,

		       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 (!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_KEY) {

			grehlen += 4;

	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)

		return;

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