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/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 69d67c3..dea9253 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2290,6 +2290,28 @@
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;
}