[PATCH 5.0 033/117] net: ip6_gre: fix possible use-after-free in ip6erspan_rcv

Greg Kroah-Hartman
2019-04-15T19:11:14Z

[ Upstream commit 2a3cabae4536edbcb21d344e7aa8be7a584d2afb ]

erspan_v6 tunnels run __iptunnel_pull_header on received skbs to remove
erspan header. This can determine a possible use-after-free accessing
pkt_md pointer in ip6erspan_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: 1d7e2ed22f8d ("net: erspan: refactor existing erspan code")
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv6/ip6_gre.c | 21 +++++++++++++--------
1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 26f25b6e2833..438f1a5fd19a 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -524,11 +524,10 @@ static int ip6gre_rcv(struct sk_buff *skb, const struct tnl_ptk_info *tpi)
return PACKET_REJECT;
}

-static int ip6erspan_rcv(struct sk_buff *skb, int gre_hdr_len,
- struct tnl_ptk_info *tpi)
+static int ip6erspan_rcv(struct sk_buff *skb, struct tnl_ptk_info *tpi,
+ int gre_hdr_len)
{
struct erspan_base_hdr *ershdr;
- struct erspan_metadata *pkt_md;
const struct ipv6hdr *ipv6h;
struct erspan_md2 *md2;
struct ip6_tnl *tunnel;
@@ -547,18 +546,16 @@ static int ip6erspan_rcv(struct sk_buff *skb, int gre_hdr_len,
if (unlikely(!pskb_may_pull(skb, len)))
return PACKET_REJECT;

- ershdr = (struct erspan_base_hdr *)skb->data;
- pkt_md = (struct erspan_metadata *)(ershdr + 1);
-
if (__iptunnel_pull_header(skb, len,
htons(ETH_P_TEB),
false, false) < 0)
return PACKET_REJECT;

if (tunnel->parms.collect_md) {
+ struct erspan_metadata *pkt_md, *md;
struct metadata_dst *tun_dst;
struct ip_tunnel_info *info;
- struct erspan_metadata *md;
+ unsigned char *gh;
__be64 tun_id;
__be16 flags;

@@ -571,6 +568,14 @@ static int ip6erspan_rcv(struct sk_buff *skb, int gre_hdr_len,
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+ * old pkt_md is no longer valid and we need to reset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));
info = &tun_dst->u.tun_info;
md = ip_tunnel_info_opts(info);
md->version = ver;
@@ -607,7 +612,7 @@ static int gre_rcv(struct sk_buff *skb)

if (unlikely(tpi.proto == htons(ETH_P_ERSPAN) ||
tpi.proto == htons(ETH_P_ERSPAN2))) {
- if (ip6erspan_rcv(skb, hdr_len, &tpi) == PACKET_RCVD)
+ if (ip6erspan_rcv(skb, &tpi, hdr_len) == PACKET_RCVD)
return 0;
goto out;
}
--
2.19.1