[PATCH net] net: fix information leakage in /proc/net/ptype

[Congyu Liu]

In one net namespace, after creating a packet socket without binding
it to a device, users in other net namespaces can observe the new
`packet_type` added by this packet socket by reading `/proc/net/ptype`
file. I believe this is minor information leakage as packet socket is
namespace aware.

Add a function pointer in `packet_type` to retrieve the net namespace
of corresponding packet socket. In `ptype_seq_show`, if this
function pointer is not NULL, use it to determine if certain ptype
should be shown.

Signed-off-by: Congyu Liu <liu3101@xxxxxxxxxx>
---
 include/linux/netdevice.h |  1 +
 net/core/net-procfs.c     |  3 ++-
 net/packet/af_packet.c    | 18 ++++++++++++++++++
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 3213c7227b59..72d3601850c5 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2548,6 +2548,7 @@ struct packet_type {
 					      struct net_device *);
 	bool			(*id_match)(struct packet_type *ptype,
 					    struct sock *sk);
+	struct net		*(*get_net) (struct packet_type *ptype);
 	void			*af_packet_priv;
 	struct list_head	list;
 };
diff --git a/net/core/net-procfs.c b/net/core/net-procfs.c
index d8b9dbabd4a4..fd5e8682058c 100644
--- a/net/core/net-procfs.c
+++ b/net/core/net-procfs.c
@@ -260,7 +260,8 @@ static int ptype_seq_show(struct seq_file *seq, void *v)
 
 	if (v == SEQ_START_TOKEN)
 		seq_puts(seq, "Type Device      Function\n");
-	else if (pt->dev == NULL || dev_net(pt->dev) == seq_file_net(seq)) {
+	else if ((pt->get_net && net_eq(pt->get_net(pt), seq_file_net(seq))) ||
+		 (!pt->get_net && (pt->dev == NULL || dev_net(pt->dev) == seq_file_net(seq)))) {
 		if (pt->type == htons(ETH_P_ALL))
 			seq_puts(seq, "ALL ");
 		else
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 5bd409ab4cc2..7997b9db8280 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1678,6 +1678,14 @@ static bool fanout_find_new_id(struct sock *sk, u16 *new_id)
 	return false;
 }
 
+static struct net *fanout_ptype_get_net(struct packet_type *pt)
+{
+	struct packet_fanout *f;
+
+	f = pt->af_packet_priv;
+	return read_pnet(&f->net);
+}
+
 static int fanout_add(struct sock *sk, struct fanout_args *args)
 {
 	struct packet_rollover *rollover = NULL;
@@ -1774,6 +1782,7 @@ static int fanout_add(struct sock *sk, struct fanout_args *args)
 		match->prot_hook.dev = po->prot_hook.dev;
 		match->prot_hook.func = packet_rcv_fanout;
 		match->prot_hook.af_packet_priv = match;
+		match->prot_hook.get_net = fanout_ptype_get_net;
 		match->prot_hook.id_match = match_fanout_group;
 		match->max_num_members = args->max_num_members;
 		list_add(&match->list, &fanout_list);
@@ -3294,6 +3303,14 @@ static struct proto packet_proto = {
 	.obj_size = sizeof(struct packet_sock),
 };
 
+static struct net *packet_ptype_get_net(struct packet_type *pt)
+{
+	struct sock *sk;
+
+	sk = pt->af_packet_priv;
+	return sock_net(sk);
+}
+
 /*
  *	Create a packet of type SOCK_PACKET.
  */
@@ -3353,6 +3370,7 @@ static int packet_create(struct net *net, struct socket *sock, int protocol,
 		po->prot_hook.func = packet_rcv_spkt;
 
 	po->prot_hook.af_packet_priv = sk;
+	po->prot_hook.get_net = packet_ptype_get_net;
 
 	if (proto) {
 		po->prot_hook.type = proto;
-- 
2.25.1