[PATCH 3.11 044/208] ping: prevent NULL pointer dereference on write to msg_name

[Luis Henriques]

3.11.10.2 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Hannes Frederic Sowa <hannes at stressinduktion.org>

commit cf970c002d270c36202bd5b9c2804d3097a52da0 upstream.

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 at stressinduktion.org>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/ipv4/ping.c | 34 +++++++++++++++++++---------------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
index d7886b2..d243eef 100644
--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c
@@ -868,11 +868,13 @@ 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);
@@ -884,16 +886,18 @@ 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);
-- 
1.8.3.2