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ip6_gre: fix ip6gre_err() invalid reads

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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: c12b395a46 ("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>
This commit is contained in:
Eric Dumazet 2017-02-04 23:18:55 -08:00 committed by David S. Miller
parent d71b789688
commit 7892032cfe
1 changed files with 21 additions and 19 deletions
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40
net/ipv6/ip6_gre.c
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@ -367,35 +367,37 @@ 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)
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)
return;