[Devel] [PATCH 2/3] netlink: add an ability to restore messages in a receive queue

[Andrey Vagin]

This patch adds an repair mode for netlink sockets. sendmsg queues
messages into a receive queue if a socket is in the repair mode.
---
 include/uapi/linux/netlink.h | 19 ++++++++++-------
 net/netlink/af_netlink.c     | 51 +++++++++++++++++++++++++++++++-------------
 2 files changed, 47 insertions(+), 23 deletions(-)

diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h
index 3e34b7d..56ddadf 100644
--- a/include/uapi/linux/netlink.h
+++ b/include/uapi/linux/netlink.h
@@ -101,14 +101,17 @@ struct nlmsgerr {
 	struct nlmsghdr msg;
 };
 
-#define NETLINK_ADD_MEMBERSHIP	1
-#define NETLINK_DROP_MEMBERSHIP	2
-#define NETLINK_PKTINFO		3
-#define NETLINK_BROADCAST_ERROR	4
-#define NETLINK_NO_ENOBUFS	5
-#define NETLINK_RX_RING		6
-#define NETLINK_TX_RING		7
-#define NETLINK_LISTEN_ALL_NSID	8
+#define NETLINK_ADD_MEMBERSHIP		1
+#define NETLINK_DROP_MEMBERSHIP		2
+#define NETLINK_PKTINFO			3
+#define NETLINK_BROADCAST_ERROR		4
+#define NETLINK_NO_ENOBUFS		5
+#define NETLINK_RX_RING			6
+#define NETLINK_TX_RING			7
+#define NETLINK_LISTEN_ALL_NSID		8
+#define NETLINK_LIST_MEMBERSHIPS	9
+#define NETLINK_CAP_ACK			10
+#define NETLINK_REPAIR			11
 
 struct nl_pktinfo {
 	__u32	group;
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 79526e5..113e2ae 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -83,6 +83,8 @@ 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
+#define NETLINK_F_REPAIR		0x40
 
 static inline int netlink_is_kernel(struct sock *sk)
 {
@@ -1744,6 +1746,7 @@ static int netlink_unicast_kernel(struct sock *sk, struct sk_buff *skb,
 int netlink_unicast(struct sock *ssk, struct sk_buff *skb,
 		    u32 portid, int nonblock)
 {
+	struct netlink_sock *nlk = nlk_sk(ssk);
 	struct sock *sk;
 	int err;
 	long timeo;
@@ -1752,19 +1755,24 @@ int netlink_unicast(struct sock *ssk, struct sk_buff *skb,
 
 	timeo = sock_sndtimeo(ssk, nonblock);
 retry:
-	sk = netlink_getsockbyportid(ssk, portid);
-	if (IS_ERR(sk)) {
-		kfree_skb(skb);
-		return PTR_ERR(sk);
-	}
-	if (netlink_is_kernel(sk))
-		return netlink_unicast_kernel(sk, skb, ssk);
+	if (nlk->flags & NETLINK_F_REPAIR) {
+		sk = ssk;
+		sock_hold(sk);
+	} else {
+		sk = netlink_getsockbyportid(ssk, portid);
+		if (IS_ERR(sk)) {
+			kfree_skb(skb);
+			return PTR_ERR(sk);
+		}
+		if (netlink_is_kernel(sk))
+			return netlink_unicast_kernel(sk, skb, ssk);
 
-	if (sk_filter(sk, skb)) {
-		err = skb->len;
-		kfree_skb(skb);
-		sock_put(sk);
-		return err;
+		if (sk_filter(sk, skb)) {
+			err = skb->len;
+			kfree_skb(skb);
+			sock_put(sk);
+			return err;
+		}
 	}
 
 	err = netlink_attachskb(sk, skb, &timeo, ssk);
@@ -2126,6 +2134,13 @@ static int netlink_setsockopt(struct socket *sock, int level, int optname,
 		return -EFAULT;
 
 	switch (optname) {
+	case NETLINK_REPAIR:
+		if (val)
+			nlk->flags |= NETLINK_F_REPAIR;
+		else
+			nlk->flags &= ~NETLINK_F_REPAIR;
+		err = 0;
+		break;
 	case NETLINK_PKTINFO:
 		if (val)
 			nlk->flags |= NETLINK_F_RECV_PKTINFO;
@@ -2288,6 +2303,7 @@ static int netlink_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	int err;
 	struct scm_cookie scm;
 	u32 netlink_skb_flags = 0;
+	bool repair = nlk->flags & NETLINK_F_REPAIR;
 
 	if (msg->msg_flags&MSG_OOB)
 		return -EOPNOTSUPP;
@@ -2307,7 +2323,8 @@ static int netlink_sendmsg(struct kiocb *kiocb, struct socket *sock,
 		dst_group = ffs(addr->nl_groups);
 		err =  -EPERM;
 		if ((dst_group || dst_portid) &&
-		    !netlink_allowed(sock, NL_CFG_F_NONROOT_SEND))
+		    !netlink_allowed(sock, NL_CFG_F_NONROOT_SEND &&
+		    !repair))
 			goto out;
 		netlink_skb_flags |= NETLINK_SKB_DST;
 	} else {
@@ -2336,7 +2353,11 @@ static int netlink_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	if (skb == NULL)
 		goto out;
 
-	NETLINK_CB(skb).portid	= nlk->portid;
+	if (unlikely(repair))
+		NETLINK_CB(skb).portid = dst_portid;
+	else
+		NETLINK_CB(skb).portid	= nlk->portid;
+
 	NETLINK_CB(skb).dst_group = dst_group;
 	NETLINK_CB(skb).creds	= siocb->scm->creds;
 	NETLINK_CB(skb).flags	= netlink_skb_flags;
@@ -2353,7 +2374,7 @@ static int netlink_sendmsg(struct kiocb *kiocb, struct socket *sock,
 		goto out;
 	}
 
-	if (dst_group) {
+	if (dst_group && !repair) {
 		atomic_inc(&skb->users);
 		netlink_broadcast(sk, skb, dst_portid, dst_group, GFP_KERNEL);
 	}
-- 
2.5.5