netlink: Don't shift on 64 for ngroups

It's legal to have 64 groups for netlink_sock.

As user-supplied nladdr->nl_groups is __u32, it's possible to subscribe only to first 32 groups.

The check for correctness of .bind() userspace supplied parameter is done by applying mask made from ngroups shift. Which broke Android as they have 64 groups and the shift for mask resulted in an overflow.

---
v2:
sizeof() is in bytes

 net/netlink/af_netlink.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index 7d860a22e5fb..d6ff4d409437 100644
@@ -1011,8 +1011,8 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr,
 
 	if (nlk->ngroups == 0)
 		groups = 0;
-	else
-		groups &= (1ULL << nlk->ngroups) - 1;
+	else if (nlk->ngroups < 8*sizeof(groups))
+		groups &= (1UL << nlk->ngroups) - 1;
 
 	bound = nlk->bound;
 	if (bound) {

2.13.6

From: Dmitry Safonov <[email protected]>
Date: Sun, 5 Aug 2018 01:35:53 +0100

Applied and queued up for -stable.