[PATCH 3.16 305/366] netlink: Don't shift with UB on nlk->ngroups

[Ben Hutchings]

3.16.61-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Dmitry Safonov <dima@xxxxxxxxxx>

commit 61f4b23769f0cc72ae62c9a81cf08f0397d40da8 upstream.

On i386 nlk->ngroups might be 32 or 0. Which leads to UB, resulting in
hang during boot.
Check for 0 ngroups and use (unsigned long long) as a type to shift.

Fixes: 7acf9d4237c4 ("netlink: Do not subscribe to non-existent groups").
Reported-by: kernel test robot <rong.a.chen@xxxxxxxxx>
Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/netlink/af_netlink.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -927,7 +927,11 @@ static int netlink_bind(struct socket *s
 		if (err)
 			return err;
 	}
-	groups &= (1UL << nlk->ngroups) - 1;
+
+	if (nlk->ngroups == 0)
+		groups = 0;
+	else
+		groups &= (1ULL << nlk->ngroups) - 1;
 
 	if (nlk->portid)
 		if (nladdr->nl_pid != nlk->portid)