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 <dh.herrmann@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h
index 3e34b7d702f8a4884ee15afeca35c651861d40bc..cf6a65cccbdf565a10af8f9a094334d070165ebb 100644 (file)
--- 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
index 69d67c300b80de2963e1ec23621b13ac4f66377f..dea925388a5b7a86ba649f888fb10bb805f54edb 100644 (file)
--- 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;
        }