sock_diag: request _diag module only when the family or proto has been registered

Now when using 'ss' in iproute, kernel would try to load all _diag
modules, which also causes corresponding family and proto modules
to be loaded as well due to module dependencies.

Like after running 'ss', sctp, dccp, af_packet (if it works as a module)
would be loaded.

For example:

  $ lsmod|grep sctp
  $ ss
  $ lsmod|grep sctp
  sctp_diag              16384  0
  sctp                  323584  5 sctp_diag
  inet_diag              24576  4 raw_diag,tcp_diag,sctp_diag,udp_diag
  libcrc32c              16384  3 nf_conntrack,nf_nat,sctp

As these family and proto modules are loaded unintentionally, it
could cause some problems, like:

- Some debug tools use 'ss' to collect the socket info, which loads all
  those diag and family and protocol modules. It's noisy for identifying
  issues.

- Users usually expect to drop sctp init packet silently when they
  have no sense of sctp protocol instead of sending abort back.

- It wastes resources (especially with multiple netns), and SCTP module
  can't be unloaded once it's loaded.

...

In short, it's really inappropriate to have these family and proto
modules loaded unexpectedly when just doing debugging with inet_diag.

This patch is to introduce sock_load_diag_module() where it loads
the _diag module only when it's corresponding family or proto has
been already registered.

Note that we can't just load _diag module without the family or
proto loaded, as some symbols used in _diag module are from the
family or proto module.

v1->v2:
  - move inet proto check to inet_diag to avoid a compiling err.
v2->v3:
  - define sock_load_diag_module in sock.c and export one symbol
    only.
  - improve the changelog.

Reported-by: Sabrina Dubroca <sd@queasysnail.net>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Acked-by: Phil Sutter <phil@nwl.cc>
Acked-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 31 insertions, 10 deletions

diff --git a/net/core/sock.c b/net/core/sock.c
index c501499a04fe..85b0b64e7f9d 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -3261,6 +3261,27 @@ void proto_unregister(struct proto *prot)
 }
 EXPORT_SYMBOL(proto_unregister);
 
+int sock_load_diag_module(int family, int protocol)
+{
+	if (!protocol) {
+		if (!sock_is_registered(family))
+			return -ENOENT;
+
+		return request_module("net-pf-%d-proto-%d-type-%d", PF_NETLINK,
+				      NETLINK_SOCK_DIAG, family);
+	}
+
+#ifdef CONFIG_INET
+	if (family == AF_INET &&
+	    !rcu_access_pointer(inet_protos[protocol]))
+		return -ENOENT;
+#endif
+
+	return request_module("net-pf-%d-proto-%d-type-%d-%d", PF_NETLINK,
+			      NETLINK_SOCK_DIAG, family, protocol);
+}
+EXPORT_SYMBOL(sock_load_diag_module);
+
 #ifdef CONFIG_PROC_FS
 static void *proto_seq_start(struct seq_file *seq, loff_t *pos)
 	__acquires(proto_list_mutex)
diff --git a/net/core/sock_diag.c b/net/core/sock_diag.c
index 146b50e30659..c37b5be7c5e4 100644
--- a/net/core/sock_diag.c
+++ b/net/core/sock_diag.c
@@ -220,8 +220,7 @@ static int __sock_diag_cmd(struct sk_buff *skb, struct nlmsghdr *nlh)
 		return -EINVAL;
 
 	if (sock_diag_handlers[req->sdiag_family] == NULL)
-		request_module("net-pf-%d-proto-%d-type-%d", PF_NETLINK,
-				NETLINK_SOCK_DIAG, req->sdiag_family);
+		sock_load_diag_module(req->sdiag_family, 0);
 
 	mutex_lock(&sock_diag_table_mutex);
 	hndl = sock_diag_handlers[req->sdiag_family];
@@ -247,8 +246,7 @@ static int sock_diag_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
 	case TCPDIAG_GETSOCK:
 	case DCCPDIAG_GETSOCK:
 		if (inet_rcv_compat == NULL)
-			request_module("net-pf-%d-proto-%d-type-%d", PF_NETLINK,
-					NETLINK_SOCK_DIAG, AF_INET);
+			sock_load_diag_module(AF_INET, 0);
 
 		mutex_lock(&sock_diag_table_mutex);
 		if (inet_rcv_compat != NULL)
@@ -281,14 +279,12 @@ static int sock_diag_bind(struct net *net, int group)
 	case SKNLGRP_INET_TCP_DESTROY:
 	case SKNLGRP_INET_UDP_DESTROY:
 		if (!sock_diag_handlers[AF_INET])
-			request_module("net-pf-%d-proto-%d-type-%d", PF_NETLINK,
-				       NETLINK_SOCK_DIAG, AF_INET);
+			sock_load_diag_module(AF_INET, 0);
 		break;
 	case SKNLGRP_INET6_TCP_DESTROY:
 	case SKNLGRP_INET6_UDP_DESTROY:
 		if (!sock_diag_handlers[AF_INET6])
-			request_module("net-pf-%d-proto-%d-type-%d", PF_NETLINK,
-				       NETLINK_SOCK_DIAG, AF_INET6);
+			sock_load_diag_module(AF_INET6, 0);
 		break;
 	}
 	return 0;
diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index a383f299ce24..4e5bc4b2f14e 100644
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -53,8 +53,7 @@ static DEFINE_MUTEX(inet_diag_table_mutex);
 static const struct inet_diag_handler *inet_diag_lock_handler(int proto)
 {
 	if (!inet_diag_table[proto])
-		request_module("net-pf-%d-proto-%d-type-%d-%d", PF_NETLINK,
-			       NETLINK_SOCK_DIAG, AF_INET, proto);
+		sock_load_diag_module(AF_INET, proto);
 
 	mutex_lock(&inet_diag_table_mutex);
 	if (!inet_diag_table[proto])
diff --git a/net/socket.c b/net/socket.c
index a93c99b518ca..08847c3b8c39 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2587,6 +2587,11 @@ void sock_unregister(int family)
 }
 EXPORT_SYMBOL(sock_unregister);
 
+bool sock_is_registered(int family)
+{
+	return family < NPROTO && rcu_access_pointer(net_families[family]);
+}
+
 static int __init sock_init(void)
 {
 	int err;