[NETLINK]: Use group numbers instead of bitmasks internally

Using the group number allows increasing the number of groups without
beeing limited by the size of the bitmask. It introduces one limitation
for netlink users: messages can't be broadcasted to multiple groups anymore,
however this feature was never used inside the kernel.

Signed-off-by: Patrick McHardy <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/netlink.h

···
 	struct ucred		creds;		/* Skb credentials	*/
 	__u32			pid;
 	__u32			dst_pid;
-	__u32			dst_groups;
+	__u32			dst_group;
 	kernel_cap_t		eff_cap;
 	__u32			loginuid;	/* Login (audit) uid */
 };

net/netlink/af_netlink.c

···
 	u32			pid;
 	unsigned int		groups;
 	u32			dst_pid;
-	unsigned int		dst_groups;
+	u32			dst_group;
 	unsigned long		state;
 	wait_queue_head_t	wait;
 	struct netlink_callback	*cb;
···
 static atomic_t nl_table_users = ATOMIC_INIT(0);
 
 static struct notifier_block *netlink_chain;
+
+static u32 netlink_group_mask(u32 group)
+{
+	return group ? 1 << (group - 1) : 0;
+}
 
 static struct hlist_head *nl_pid_hashfn(struct nl_pid_hash *hash, u32 pid)
 {
···
 	if (addr->sa_family == AF_UNSPEC) {
 		sk->sk_state	= NETLINK_UNCONNECTED;
 		nlk->dst_pid	= 0;
-		nlk->dst_groups = 0;
+		nlk->dst_group  = 0;
 		return 0;
 	}
 	if (addr->sa_family != AF_NETLINK)
···
 	if (err == 0) {
 		sk->sk_state	= NETLINK_CONNECTED;
 		nlk->dst_pid 	= nladdr->nl_pid;
-		nlk->dst_groups = nladdr->nl_groups;
+		nlk->dst_group  = ffs(nladdr->nl_groups);
 	}
 
 	return err;
···
 
 	if (peer) {
 		nladdr->nl_pid = nlk->dst_pid;
-		nladdr->nl_groups = nlk->dst_groups;
+		nladdr->nl_groups = netlink_group_mask(nlk->dst_group);
 	} else {
 		nladdr->nl_pid = nlk->pid;
-		nladdr->nl_groups = nlk->groups;
+		nladdr->nl_groups = nlk->groups; 
 	}
 	return 0;
 }
···
 	if (p->exclude_sk == sk)
 		goto out;
 
-	if (nlk->pid == p->pid || !(nlk->groups & p->group))
+	if (nlk->pid == p->pid || !(nlk->groups & netlink_group_mask(p->group)))
 		goto out;
 
 	if (p->failure) {
···
 	if (sk == p->exclude_sk)
 		goto out;
 
-	if (nlk->pid == p->pid || !(nlk->groups & p->group))
+	if (nlk->pid == p->pid || !(nlk->groups & netlink_group_mask(p->group)))
 		goto out;
 
 	sk->sk_err = p->code;
···
 	struct netlink_sock *nlk = nlk_sk(sk);
 	struct sockaddr_nl *addr=msg->msg_name;
 	u32 dst_pid;
-	u32 dst_groups;
+	u32 dst_group;
 	struct sk_buff *skb;
 	int err;
 	struct scm_cookie scm;
···
 		if (addr->nl_family != AF_NETLINK)
 			return -EINVAL;
 		dst_pid = addr->nl_pid;
-		dst_groups = addr->nl_groups;
-		if (dst_groups && !netlink_capable(sock, NL_NONROOT_SEND))
+		dst_group = ffs(addr->nl_groups);
+		if (dst_group && !netlink_capable(sock, NL_NONROOT_SEND))
 			return -EPERM;
 	} else {
 		dst_pid = nlk->dst_pid;
-		dst_groups = nlk->dst_groups;
+		dst_group = nlk->dst_group;
 	}
 
 	if (!nlk->pid) {
···
 
 	NETLINK_CB(skb).pid	= nlk->pid;
 	NETLINK_CB(skb).dst_pid = dst_pid;
-	NETLINK_CB(skb).dst_groups = dst_groups;
+	NETLINK_CB(skb).dst_group = dst_group;
 	NETLINK_CB(skb).loginuid = audit_get_loginuid(current->audit_context);
 	memcpy(NETLINK_CREDS(skb), &siocb->scm->creds, sizeof(struct ucred));
 
···
 		goto out;
 	}
 
-	if (dst_groups) {
+	if (dst_group) {
 		atomic_inc(&skb->users);
-		netlink_broadcast(sk, skb, dst_pid, dst_groups, GFP_KERNEL);
+		netlink_broadcast(sk, skb, dst_pid, dst_group, GFP_KERNEL);
 	}
 	err = netlink_unicast(sk, skb, dst_pid, msg->msg_flags&MSG_DONTWAIT);
 
···
 		addr->nl_family = AF_NETLINK;
 		addr->nl_pad    = 0;
 		addr->nl_pid	= NETLINK_CB(skb).pid;
-		addr->nl_groups	= NETLINK_CB(skb).dst_groups;
+		addr->nl_groups	= netlink_group_mask(NETLINK_CB(skb).dst_group);
 		msg->msg_namelen = sizeof(*addr);
 	}