[PATCH for v4.9 LTS 46/86] ip6_tunnel: must reload ipv6h in ip6ip6_tnl_xmit()

[Levin, Alexander (Sasha Levin)]

From: Eric Dumazet <eduma...@google.com>

[ Upstream commit 21b995a9cb093fff33ec91d7cb3822b882a90a1e ]

Since ip6_tnl_parse_tlv_enc_lim() can call pskb_may_pull(),
we must reload any pointer that was related to skb->head
(or skb->data), or risk use after free.

Fixes: c12b395a4664 ("gre: Support GRE over IPv6")
Signed-off-by: Eric Dumazet <eduma...@google.com>
Cc: Dmitry Kozlov <x...@mail.ru>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Sasha Levin <alexander.le...@verizon.com>
---
 net/ipv6/ip6_gre.c    | 3 +++
 net/ipv6/ip6_tunnel.c | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 0a5922055da2..a5fdc1aa7a9a 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -582,6 +582,9 @@ static inline int ip6gre_xmit_ipv6(struct sk_buff *skb, 
struct net_device *dev)
                return -1;
 
        offset = ip6_tnl_parse_tlv_enc_lim(skb, skb_network_header(skb));
+       /* ip6_tnl_parse_tlv_enc_lim() might have reallocated skb->head */
+       ipv6h = ipv6_hdr(skb);
+
        if (offset > 0) {
                struct ipv6_tlv_tnl_enc_lim *tel;
                tel = (struct ipv6_tlv_tnl_enc_lim 
*)&skb_network_header(skb)[offset];
diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 116b4da06820..63fad2467a7e 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -1313,6 +1313,8 @@ ip6ip6_tnl_xmit(struct sk_buff *skb, struct net_device 
*dev)
                fl6.flowlabel = key->label;
        } else {
                offset = ip6_tnl_parse_tlv_enc_lim(skb, 
skb_network_header(skb));
+               /* ip6_tnl_parse_tlv_enc_lim() might have reallocated skb->head 
*/
+               ipv6h = ipv6_hdr(skb);
                if (offset > 0) {
                        struct ipv6_tlv_tnl_enc_lim *tel;
 
-- 
2.11.0