ip: zero sockaddr returned on error queue

The sockaddr is returned in IP(V6)_RECVERR as part of errhdr. That
structure is defined and allocated on the stack as

    struct {
            struct sock_extended_err ee;
            struct sockaddr_in(6)    offender;
    } errhdr;

The second part is only initialized for certain SO_EE_ORIGIN values.
Always initialize it completely.

An MTU exceeded error on a SOCK_RAW/IPPROTO_RAW is one example that
would return uninitialized bytes.

Signed-off-by: Willem de Bruijn <willemb@google.com>

----

Also verified that there is no padding between errhdr.ee and
errhdr.offender that could leak additional kernel data.
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 7 deletions

diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c
index 100c589a2a6c..49f5e73db122 100644
--- a/net/ipv6/datagram.c
+++ b/net/ipv6/datagram.c
@@ -393,11 +393,10 @@ int ipv6_recv_error(struct sock *sk, struct msghdr *msg, int len, int *addr_len)
 
         memcpy(&errhdr.ee, &serr->ee, sizeof(struct sock_extended_err));
         sin = &errhdr.offender;
-        sin->sin6_family = AF_UNSPEC;
+        memset(sin, 0, sizeof(*sin));
+
         if (serr->ee.ee_origin != SO_EE_ORIGIN_LOCAL) {
                 sin->sin6_family = AF_INET6;
-                sin->sin6_flowinfo = 0;
-                sin->sin6_port = 0;
                 if (np->rxopt.all) {
                         if (serr->ee.ee_origin != SO_EE_ORIGIN_ICMP &&
                             serr->ee.ee_origin != SO_EE_ORIGIN_ICMP6)
@@ -412,12 +411,9 @@ int ipv6_recv_error(struct sock *sk, struct msghdr *msg, int len, int *addr_len)
                                 ipv6_iface_scope_id(&sin->sin6_addr,
                                                     IP6CB(skb)->iif);
                 } else {
-                        struct inet_sock *inet = inet_sk(sk);
-
                         ipv6_addr_set_v4mapped(ip_hdr(skb)->saddr,
                                                &sin->sin6_addr);
-                        sin->sin6_scope_id = 0;
-                        if (inet->cmsg_flags)
+                        if (inet_sk(sk)->cmsg_flags)
                                 ip_cmsg_recv(msg, skb);
                 }
         }