netlink: add API to retrieve all group memberships

This patch adds getsockopt(SOL_NETLINK, NETLINK_LIST_MEMBERSHIPS) to retrieve all groups a socket is a member of. Currently, we have to use getsockname() and look at the nl.nl_groups bitmask. However, this mask is limited to 32 groups. Hence, similar to NETLINK_ADD_MEMBERSHIP and NETLINK_DROP_MEMBERSHIP, this adds a separate sockopt to manager higher groups IDs than 32. This new NETLINK_LIST_MEMBERSHIPS option takes a pointer to __u32 and the size of the array. The array is filled with the full membership-set of the socket, and the required array size is returned in optlen. Hence, user-space can retry with a properly sized array in case it was too small. Signed-off-by: David Herrmann <[email protected]> Signed-off-by: David S. Miller <[email protected]>
1054009064 · Jun 21, 2015 · b42be38 · b42be38
1 parent e0df02e
commit b42be38
Show file tree

Hide file tree

Showing 2 changed files with 31 additions and 8 deletions.
diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h
@@ -101,14 +101,15 @@ 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
 
 struct nl_pktinfo {
 	__u32	group;

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
@@ -2290,6 +2290,28 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
 			return -EFAULT;
 		err = 0;
 		break;
+	case NETLINK_LIST_MEMBERSHIPS: {
+		int pos, idx, shift;
+
+		err = 0;
+		netlink_table_grab();
+		for (pos = 0; pos * 8 < nlk->ngroups; pos += sizeof(u32)) {
+			if (len - pos < sizeof(u32))
+				break;
+
+			idx = pos / sizeof(unsigned long);
+			shift = (pos % sizeof(unsigned long)) * 8;
+			if (put_user((u32)(nlk->groups[idx] >> shift),
+				     (u32 __user *)(optval + pos))) {
+				err = -EFAULT;
+				break;
+			}
+		}
+		if (put_user(ALIGN(nlk->ngroups / 8, sizeof(u32)), optlen))
+			err = -EFAULT;
+		netlink_table_ungrab();
+		break;
+	}
 	default:
 		err = -ENOPROTOOPT;
 	}