[SRU][B][PATCH] netlink: Don't shift on 64 for ngroups

[Andrea Righi]

From: Dmitry Safonov <dima at arista.com>

BugLink: https://bugs.launchpad.net/bugs/1831103

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.

Fixes: 61f4b23769f0 ("netlink: Don't shift with UB on nlk->ngroups")
Cc: "David S. Miller" <davem at davemloft.net>
Cc: Herbert Xu <herbert at gondor.apana.org.au>
Cc: Steffen Klassert <steffen.klassert at secunet.com>
Cc: netdev at vger.kernel.org
Cc: stable at vger.kernel.org
Reported-and-Tested-by: Nathan Chancellor <natechancellor at gmail.com>
Signed-off-by: Dmitry Safonov <dima at arista.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit 91874ecf32e41b5d86a4cb9d60e0bee50d828058)
Signed-off-by: Andrea Righi <andrea.righi at canonical.com>
---
 net/netlink/af_netlink.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 07e61faaea47..6db2daedf01c 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -980,8 +980,8 @@ 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) {
-- 
2.20.1