[PATCH 4.9 40/88] net: netlink: cap max groups which will be considered in netlink_bind()

[Greg Kroah-Hartman]

From: Nikolay Aleksandrov <nikolay@xxxxxxxxxxxxxxxxxxx>

commit 3a20773beeeeadec41477a5ba872175b778ff752 upstream.

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@xxxxxx>
CC: Richard Guy Briggs <rgb@xxxxxxxxxx>
Fixes: 4f520900522f ("netlink: have netlink per-protocol bind function return an error code.")
Reported-by: Erhard F. <erhard_f@xxxxxxxxxxx>
Signed-off-by: Nikolay Aleksandrov <nikolay@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 net/netlink/af_netlink.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1003,7 +1003,8 @@ static int netlink_bind(struct socket *s
 	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);
@@ -1022,7 +1023,7 @@ static int netlink_bind(struct socket *s
 			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);
 			return err;
 		}
 	}