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

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Date:   Sun, 11 Nov 2018 19:49:05 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "kernel test robot" <rong.a.chen@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Dmitry Safonov" <dima@...sta.com>
Subject: [PATCH 3.16 305/366] netlink: Don't shift with UB on nlk->ngroups

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

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

From: Dmitry Safonov <dima@...sta.com>

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@...el.com>
Signed-off-by: Dmitry Safonov <dima@...sta.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 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)