[PATCH 3.18 014/145] ip6_gre: fix ip6gre_err() invalid reads

Greg Kroah-Hartman
2017-04-16T10:51:37Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 7892032cfe67f4bde6fc2ee967e45a8fbaf33756 ]

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv6/ip6_gre.c | 41 ++++++++++++++++++++++-------------------
1 file changed, 22 insertions(+), 19 deletions(-)

--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -55,6 +55,7 @@
#include <net/ip6_fib.h>
#include <net/ip6_route.h>
#include <net/ip6_tunnel.h>
+#include <net/gre.h>

static bool log_ecn_error = true;
@@ -367,35 +368,37 @@ static void ip6gre_tunnel_uninit(struct

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;