[PATCH net 3/4] udpv6: fix possible user after free in error handler

[Paolo Abeni]

Before derefencing the encap pointer, commit e7cc082455cb ("udp: Support
for error handlers of tunnels with arbitrary destination port") checks
for a NULL value, but the two fetch operation can race with removal.
Fix the above using a single access.
Also fix a couple of type annotations, to make sparse happy.

Fixes: e7cc082455cb ("udp: Support for error handlers of tunnels with arbitrary 
destination port")
Signed-off-by: Paolo Abeni <pab...@redhat.com>
Acked-by: Stefano Brivio <sbri...@redhat.com>
---
 net/ipv6/udp.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index e6c52c27f354..b444483cdb2b 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -420,17 +420,19 @@ EXPORT_SYMBOL(udpv6_encap_enable);
  */
 static int __udp6_lib_err_encap_no_sk(struct sk_buff *skb,
                                      struct inet6_skb_parm *opt,
-                                     u8 type, u8 code, int offset, u32 info)
+                                     u8 type, u8 code, int offset, __be32 info)
 {
        int i;
 
        for (i = 0; i < MAX_IPTUN_ENCAP_OPS; i++) {
                int (*handler)(struct sk_buff *skb, struct inet6_skb_parm *opt,
-                              u8 type, u8 code, int offset, u32 info);
+                              u8 type, u8 code, int offset, __be32 info);
+               const struct ip6_tnl_encap_ops *encap;
 
-               if (!ip6tun_encaps[i])
+               encap = rcu_dereference(ip6tun_encaps[i]);
+               if (!encap)
                        continue;
-               handler = rcu_dereference(ip6tun_encaps[i]->err_handler);
+               handler = encap->err_handler;
                if (handler && !handler(skb, opt, type, code, offset, info))
                        return 0;
        }
-- 
2.20.1