ping: prevent NULL pointer dereference on write to msg_name

A plain read() on a socket does set msg->msg_name to NULL. So check for
NULL pointer first.

Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 19 insertions, 15 deletions

diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
index aacefa0caa36..91bfe0437e7a 100644
--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c
@@ -870,11 +870,13 @@ int ping_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
         if (family == AF_INET) {
                 struct sockaddr_in *sin = (struct sockaddr_in *)msg->msg_name;
 
-                sin->sin_family = AF_INET;
-                sin->sin_port = 0 /* skb->h.uh->source */;
-                sin->sin_addr.s_addr = ip_hdr(skb)->saddr;
-                memset(sin->sin_zero, 0, sizeof(sin->sin_zero));
-                *addr_len = sizeof(*sin);
+                if (sin) {
+                        sin->sin_family = AF_INET;
+                        sin->sin_port = 0 /* skb->h.uh->source */;
+                        sin->sin_addr.s_addr = ip_hdr(skb)->saddr;
+                        memset(sin->sin_zero, 0, sizeof(sin->sin_zero));
+                        *addr_len = sizeof(*sin);
+                }
 
                 if (isk->cmsg_flags)
                         ip_cmsg_recv(msg, skb);
@@ -886,16 +888,18 @@ int ping_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
                 struct sockaddr_in6 *sin6 =
                         (struct sockaddr_in6 *)msg->msg_name;
 
-                sin6->sin6_family = AF_INET6;
-                sin6->sin6_port = 0;
-                sin6->sin6_addr = ip6->saddr;
-                sin6->sin6_flowinfo = 0;
-                if (np->sndflow)
-                        sin6->sin6_flowinfo = ip6_flowinfo(ip6);
-
-                sin6->sin6_scope_id = ipv6_iface_scope_id(&sin6->sin6_addr,
-                                                          IP6CB(skb)->iif);
-                *addr_len = sizeof(*sin6);
+                if (sin6) {
+                        sin6->sin6_family = AF_INET6;
+                        sin6->sin6_port = 0;
+                        sin6->sin6_addr = ip6->saddr;
+                        sin6->sin6_flowinfo = 0;
+                        if (np->sndflow)
+                                sin6->sin6_flowinfo = ip6_flowinfo(ip6);
+                        sin6->sin6_scope_id =
+                                ipv6_iface_scope_id(&sin6->sin6_addr,
+                                                    IP6CB(skb)->iif);
+                        *addr_len = sizeof(*sin6);
+                }
 
                 if (inet6_sk(sk)->rxopt.all)
                         pingv6_ops.ip6_datagram_recv_ctl(sk, msg, skb);