1 files changed, 24 insertions, 3 deletions

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index a774985489e2..3eea0b2a3239 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -84,6 +84,7 @@ struct listeners {
 #define NETLINK_F_BROADCAST_SEND_ERROR	0x4
 #define NETLINK_F_RECV_NO_ENOBUFS	0x8
 #define NETLINK_F_LISTEN_ALL_NSID	0x10
+#define NETLINK_F_CAP_ACK		0x20
 
 static inline int netlink_is_kernel(struct sock *sk)
 {
@@ -2258,6 +2259,13 @@ static int netlink_setsockopt(struct socket *sock, int level, int optname,
 			nlk->flags &= ~NETLINK_F_LISTEN_ALL_NSID;
 		err = 0;
 		break;
+	case NETLINK_CAP_ACK:
+		if (val)
+			nlk->flags |= NETLINK_F_CAP_ACK;
+		else
+			nlk->flags &= ~NETLINK_F_CAP_ACK;
+		err = 0;
+		break;
 	default:
 		err = -ENOPROTOOPT;
 	}
@@ -2332,6 +2340,16 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
 		netlink_table_ungrab();
 		break;
 	}
+	case NETLINK_CAP_ACK:
+		if (len < sizeof(int))
+			return -EINVAL;
+		len = sizeof(int);
+		val = nlk->flags & NETLINK_F_CAP_ACK ? 1 : 0;
+		if (put_user(len, optlen) ||
+		    put_user(val, optval))
+			return -EFAULT;
+		err = 0;
+		break;
 	default:
 		err = -ENOPROTOOPT;
 	}
@@ -2873,9 +2891,12 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err)
 	struct nlmsghdr *rep;
 	struct nlmsgerr *errmsg;
 	size_t payload = sizeof(*errmsg);
+	struct netlink_sock *nlk = nlk_sk(NETLINK_CB(in_skb).sk);
 
-	/* error messages get the original request appened */
-	if (err)
+	/* Error messages get the original request appened, unless the user
+	 * requests to cap the error message.
+	 */
+	if (!(nlk->flags & NETLINK_F_CAP_ACK) && err)
 		payload += nlmsg_len(nlh);
 
 	skb = netlink_alloc_skb(in_skb->sk, nlmsg_total_size(payload),
@@ -2898,7 +2919,7 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err)
 			  NLMSG_ERROR, payload, 0);
 	errmsg = nlmsg_data(rep);
 	errmsg->error = err;
-	memcpy(&errmsg->msg, nlh, err ? nlh->nlmsg_len : sizeof(*nlh));
+	memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg) ? nlh->nlmsg_len : sizeof(*nlh));
 	netlink_unicast(in_skb->sk, skb, NETLINK_CB(in_skb).portid, MSG_DONTWAIT);
 }
 EXPORT_SYMBOL(netlink_ack);