net/netlink: fix NETLINK_LIST_MEMBERSHIPS length report

The current code for the length calculation wrongly truncates the reported
length of the groups array, causing an under report of the subscribed
groups. To fix this, use 'BITS_TO_BYTES()' which rounds up the
division by 8.

Fixes: b42be38b2778 ("netlink: add API to retrieve all group memberships")
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20230529153335.389815-1-pctammela@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index c878041..3a1e0fd 100644 (file)
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1779,7 +1779,7 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
                                break;
                        }
                }
-               if (put_user(ALIGN(nlk->ngroups / 8, sizeof(u32)), optlen))
+               if (put_user(ALIGN(BITS_TO_BYTES(nlk->ngroups), sizeof(u32)), optlen))
                        err = -EFAULT;
                netlink_unlock_table();
                return err;