sctp: avoid auth_enable sysctl UAF during netns teardown

commit f8d5e78 upstream.

proc_sctp_do_auth() updates the SCTP control socket after changing
net.sctp.auth_enable. The handler gets the per-net SCTP state from
ctl->data, so an already opened sysctl file can still target a network
namespace while that namespace is being torn down.

SCTP previously registered its per-net sysctls from sctp_defaults_init(),
while the control socket is created later from sctp_ctrlsock_init(). This
exposed a window during initialization where auth_enable was writable
before net->sctp.ctl_sock existed, and a teardown window where auth_enable
stayed writable after inet_ctl_sock_destroy() had released the control
socket.

Move the per-net SCTP sysctl registration into sctp_ctrlsock_init() after
sctp_ctl_sock_init() succeeds, and unregister the sysctl table before
destroying the control socket in sctp_ctrlsock_exit(). If sysctl
registration fails after the control socket was created, destroy the
control socket in the same init path.

Make sctp_sysctl_net_unregister() tolerate a missing header and clear the
saved pointer so init-error and exit paths can safely share the unregister
helper.

Fixes: 15649fd ("sctp: sysctl: auth_enable: avoid using current->nsproxy")
Cc: stable@vger.kernel.org
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Co-developed-by: Qi Tang <tpluszz77@gmail.com>
Signed-off-by: Qi Tang <tpluszz77@gmail.com>
Signed-off-by: Zhiling Zou <roxy520tt@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Acked-by: Xin Long <lucien.xin@gmail.com>
Link: https://patch.msgid.link/390cd5e91ed60eea27b0b64d0468301a9e73b808.1784033357.git.roxy520tt@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: rr00xxyy

net/sctp/protocol.c

@@ -1397,10 +1397,6 @@ static int __net_init sctp_defaults_init(struct net *net)
 	net->sctp.l3mdev_accept = 1;
 #endif
 
-	status = sctp_sysctl_net_register(net);
-	if (status)
-		goto err_sysctl_register;
-
 	/* Allocate and initialise sctp mibs.  */
 	status = init_sctp_mibs(net);
 	if (status)
@@ -1434,8 +1430,6 @@ static int __net_init sctp_defaults_init(struct net *net)
 	cleanup_sctp_mibs(net);
 #endif
 err_init_mibs:
-	sctp_sysctl_net_unregister(net);
-err_sysctl_register:
 	return status;
 }
 
@@ -1450,7 +1444,6 @@ static void __net_exit sctp_defaults_exit(struct net *net)
 	net->sctp.proc_net_sctp = NULL;
 #endif
 	cleanup_sctp_mibs(net);
-	sctp_sysctl_net_unregister(net);
 }
 
 static struct pernet_operations sctp_defaults_ops = {
@@ -1464,16 +1457,27 @@ static int __net_init sctp_ctrlsock_init(struct net *net)
 
 	/* Initialize the control inode/socket for handling OOTB packets.  */
 	status = sctp_ctl_sock_init(net);
-	if (status)
+	if (status) {
 		pr_err("Failed to initialize the SCTP control sock\n");
+		return status;
+	}
+
+	status = sctp_sysctl_net_register(net);
+	if (status) {
+		inet_ctl_sock_destroy(net->sctp.ctl_sock);
+		net->sctp.ctl_sock = NULL;
+	}
 
 	return status;
 }
 
 static void __net_exit sctp_ctrlsock_exit(struct net *net)
 {
+	sctp_sysctl_net_unregister(net);
+
 	/* Free the control endpoint.  */
 	inet_ctl_sock_destroy(net->sctp.ctl_sock);
+	net->sctp.ctl_sock = NULL;
 }
 
 static struct pernet_operations sctp_ctrlsock_ops = {

net/sctp/sysctl.c

@@ -626,11 +626,16 @@ int sctp_sysctl_net_register(struct net *net)
 
 void sctp_sysctl_net_unregister(struct net *net)
 {
+	struct ctl_table_header *header = net->sctp.sysctl_header;
 	const struct ctl_table *table;
 
-	table = net->sctp.sysctl_header->ctl_table_arg;
-	unregister_net_sysctl_table(net->sctp.sysctl_header);
+	if (!header)
+		return;
+
+	table = header->ctl_table_arg;
+	unregister_net_sysctl_table(header);
 	kfree(table);
+	net->sctp.sysctl_header = NULL;
 }
 
 static struct ctl_table_header *sctp_sysctl_header;