compat: ip6_gre: fix possible use-after-free in ip6erspan_rcv

Upstream commit:
    commit 2a3cabae4536edbcb21d344e7aa8be7a584d2afb
    Author: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
    Date:   Sat Apr 6 17:16:53 2019 +0200

    net: ip6_gre: fix possible use-after-free in ip6erspan_rcv

    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>
Fixes: c387d8177f20 ("compat: Add ipv6 GRE and IPV6 Tunneling")
Cc: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Acked-by: William Tu <u9012063@gmail.com>
Signed-off-by: Greg Rose <gvrose8192@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

diff --git a/datapath/linux/compat/ip6_gre.c b/datapath/linux/compat/ip6_gre.c
index a2cc45de5af8f11437344612b938a086730a3831..afff817ecade3c2bfeafe6ee91eaeb8886b88bcd 100644 (file)
--- a/datapath/linux/compat/ip6_gre.c
+++ b/datapath/linux/compat/ip6_gre.c
@@ -538,11 +538,11 @@ static int ip6gre_rcv(struct sk_buff *skb, const struct tnl_ptk_info *tpi)
        return PACKET_RCVD;
 }
 
-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;
@@ -566,17 +566,15 @@ 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 ip_tunnel_info *info;
-                       struct erspan_metadata *md;
+                       unsigned char *gh;
                        __be64 tun_id;
                        __be16 flags;
 
@@ -589,6 +587,14 @@ 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;
@@ -623,7 +629,7 @@ 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;
        }