[PATCHv2] netlink: Don't shift on 64 for ngroups

[PATCHv2] netlink: Don't shift on 64 for ngroups

[Dmitry Safonov]

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@davemloft.net>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: netdev@vger.kernel.org
Cc: stable@vger.kernel.org
Reported-and-Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
---
v2:
  sizeof() is in bytes

 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 7d860a22e5fb..d6ff4d409437 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -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

Re: [PATCHv2] netlink: Don't shift on 64 for ngroups

[David Miller]

From: Dmitry Safonov <dima@arista.com>
Date: Sun,  5 Aug 2018 01:35:53 +0100

> 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")
> Reported-and-Tested-by: Nathan Chancellor <natechancellor@gmail.com>
> Signed-off-by: Dmitry Safonov <dima@arista.com>

Applied and queued up for -stable.