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net: ip_gre: fix possible use-after-free in erspan_rcv

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erspan tunnels run __iptunnel_pull_header on received skbs to remove
gre and erspan headers. This can determine a possible use-after-free
accessing pkt_md pointer in erspan_rcv since the packet will be 'uncloned'
running pskb_expand_head if it is a cloned gso skb (e.g if the packet has
been sent though a veth device). Fix it resetting pkt_md pointer after
__iptunnel_pull_header

Fixes: 1d7e2ed22f ("net: erspan: refactor existing erspan code")
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Lorenzo Bianconi 2019-04-06 17:16:52 +02:00 committed by David S. Miller
parent b75bb8a5b7
commit 492b67e28e
1 changed files with 10 additions and 5 deletions
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15
net/ipv4/ip_gre.c
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@ -259,7 +259,6 @@ static int erspan_rcv(struct sk_buff *skb, struct tnl_ptk_info *tpi,
struct net *net = dev_net(skb->dev);
struct metadata_dst *tun_dst = NULL;
struct erspan_base_hdr *ershdr;
struct erspan_metadata *pkt_md;
struct ip_tunnel_net *itn;
struct ip_tunnel *tunnel;
const struct iphdr *iph;
@ -282,9 +281,6 @@ static int erspan_rcv(struct sk_buff *skb, struct tnl_ptk_info *tpi,
if (unlikely(!pskb_may_pull(skb, len)))
return PACKET_REJECT;
ershdr = (struct erspan_base_hdr *)(skb->data + gre_hdr_len);
pkt_md = (struct erspan_metadata *)(ershdr + 1);
if (__iptunnel_pull_header(skb,
len,
htons(ETH_P_TEB),
@ -292,8 +288,9 @@ static int erspan_rcv(struct sk_buff *skb, struct tnl_ptk_info *tpi,
goto drop;
if (tunnel->collect_md) {
struct erspan_metadata *pkt_md, *md;
struct ip_tunnel_info *info;
struct erspan_metadata *md;
unsigned char *gh;
__be64 tun_id;
__be16 flags;
@ -306,6 +303,14 @@ static int erspan_rcv(struct sk_buff *skb, struct tnl_ptk_info *tpi,
if (!tun_dst)
return PACKET_REJECT;
/* skb can be uncloned in __iptunnel_pull_header, so
* old pkt_md is no longer valid and we need to reset
* it
*/
gh = skb_network_header(skb) +
skb_network_header_len(skb);
pkt_md = (struct erspan_metadata *)(gh + gre_hdr_len +
sizeof(*ershdr));
md = ip_tunnel_info_opts(&tun_dst->u.tun_info);
md->version = ver;
md2 = &md->u.md2;