net: netlink: cap max groups which will be considered in netlink_bind()

Since nl_groups is a u32 we can't bind more groups via ->bind
(netlink_bind) call, but netlink has supported more groups via
setsockopt() for a long time and thus nlk->ngroups could be over 32.
Recently I added support for per-vlan notifications and increased the
groups to 33 for NETLINK_ROUTE which exposed an old bug in the
netlink_bind() code causing out-of-bounds access on archs where unsigned
long is 32 bits via test_bit() on a local variable. Fix this by capping the
maximum groups in netlink_bind() to BITS_PER_TYPE(u32), effectively
capping them at 32 which is the minimum of allocated groups and the
maximum groups which can be bound via netlink_bind().

CC: Christophe Leroy <christophe.leroy@c-s.fr>
CC: Richard Guy Briggs <rgb@redhat.com>
Fixes: 4f520900522f ("netlink: have netlink per-protocol bind function return an error code.")
Reported-by: Erhard F. <erhard_f@mailbox.org>
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.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 4e31721..edf3e28 100644 (file)
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1014,7 +1014,8 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr,
        if (nlk->netlink_bind && groups) {
                int group;
 
-               for (group = 0; group < nlk->ngroups; group++) {
+               /* nl_groups is a u32, so cap the maximum groups we can bind */
+               for (group = 0; group < BITS_PER_TYPE(u32); group++) {
                        if (!test_bit(group, &groups))
                                continue;
                        err = nlk->netlink_bind(net, group + 1);
@@ -1033,7 +1034,7 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr,
                        netlink_insert(sk, nladdr->nl_pid) :
                        netlink_autobind(sock);
                if (err) {
-                       netlink_undo_bind(nlk->ngroups, groups, sk);
+                       netlink_undo_bind(BITS_PER_TYPE(u32), groups, sk);
                        goto unlock;
                }
        }