Commit 9ca5e7ec authored by Shigeru Yoshida's avatar Shigeru Yoshida Committed by David S. Miller
Browse files

l2tp: Avoid possible recursive deadlock in l2tp_tunnel_register() 



When a file descriptor of pppol2tp socket is passed as file descriptor
of UDP socket, a recursive deadlock occurs in l2tp_tunnel_register().
This situation is reproduced by the following program:

int main(void)
{
	int sock;
	struct sockaddr_pppol2tp addr;

	sock = socket(AF_PPPOX, SOCK_DGRAM, PX_PROTO_OL2TP);
	if (sock < 0) {
		perror("socket");
		return 1;
	}

	addr.sa_family = AF_PPPOX;
	addr.sa_protocol = PX_PROTO_OL2TP;
	addr.pppol2tp.pid = 0;
	addr.pppol2tp.fd = sock;
	addr.pppol2tp.addr.sin_family = PF_INET;
	addr.pppol2tp.addr.sin_port = htons(0);
	addr.pppol2tp.addr.sin_addr.s_addr = inet_addr("192.168.0.1");
	addr.pppol2tp.s_tunnel = 1;
	addr.pppol2tp.s_session = 0;
	addr.pppol2tp.d_tunnel = 0;
	addr.pppol2tp.d_session = 0;

	if (connect(sock, (const struct sockaddr *)&addr, sizeof(addr)) < 0) {
		perror("connect");
		return 1;
	}

	return 0;
}

This program causes the following lockdep warning:

 ============================================
 WARNING: possible recursive locking detected
 6.2.0-rc5-00205-gc96618275234 #56 Not tainted
 --------------------------------------------
 repro/8607 is trying to acquire lock:
 ffff8880213c8130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: l2tp_tunnel_register+0x2b7/0x11c0

 but task is already holding lock:
 ffff8880213c8130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: pppol2tp_connect+0xa82/0x1a30

 other info that might help us debug this:
  Possible unsafe locking scenario:

        CPU0
        ----
   lock(sk_lock-AF_PPPOX);
   lock(sk_lock-AF_PPPOX);

  *** DEADLOCK ***

  May be due to missing lock nesting notation

 1 lock held by repro/8607:
  #0: ffff8880213c8130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: pppol2tp_connect+0xa82/0x1a30

 stack backtrace:
 CPU: 0 PID: 8607 Comm: repro Not tainted 6.2.0-rc5-00205-gc96618275234 #56
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014
 Call Trace:
  <TASK>
  dump_stack_lvl+0x100/0x178
  __lock_acquire.cold+0x119/0x3b9
  ? lockdep_hardirqs_on_prepare+0x410/0x410
  lock_acquire+0x1e0/0x610
  ? l2tp_tunnel_register+0x2b7/0x11c0
  ? lock_downgrade+0x710/0x710
  ? __fget_files+0x283/0x3e0
  lock_sock_nested+0x3a/0xf0
  ? l2tp_tunnel_register+0x2b7/0x11c0
  l2tp_tunnel_register+0x2b7/0x11c0
  ? sprintf+0xc4/0x100
  ? l2tp_tunnel_del_work+0x6b0/0x6b0
  ? debug_object_deactivate+0x320/0x320
  ? lockdep_init_map_type+0x16d/0x7a0
  ? lockdep_init_map_type+0x16d/0x7a0
  ? l2tp_tunnel_create+0x2bf/0x4b0
  ? l2tp_tunnel_create+0x3c6/0x4b0
  pppol2tp_connect+0x14e1/0x1a30
  ? pppol2tp_put_sk+0xd0/0xd0
  ? aa_sk_perm+0x2b7/0xa80
  ? aa_af_perm+0x260/0x260
  ? bpf_lsm_socket_connect+0x9/0x10
  ? pppol2tp_put_sk+0xd0/0xd0
  __sys_connect_file+0x14f/0x190
  __sys_connect+0x133/0x160
  ? __sys_connect_file+0x190/0x190
  ? lockdep_hardirqs_on+0x7d/0x100
  ? ktime_get_coarse_real_ts64+0x1b7/0x200
  ? ktime_get_coarse_real_ts64+0x147/0x200
  ? __audit_syscall_entry+0x396/0x500
  __x64_sys_connect+0x72/0xb0
  do_syscall_64+0x38/0xb0
  entry_SYSCALL_64_after_hwframe+0x63/0xcd

This patch fixes the issue by getting/creating the tunnel before
locking the pppol2tp socket.

Fixes: 0b2c5972 ("l2tp: close all race conditions in l2tp_tunnel_register()")
Cc: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: default avatarShigeru Yoshida <syoshida@redhat.com>
Reviewed-by: default avatarGuillaume Nault <gnault@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 43686409

net/l2tp/l2tp_ppp.c

+67 −58
Original line number Diff line number Diff line
@@ -650,54 +650,22 @@ static int pppol2tp_tunnel_mtu(const struct l2tp_tunnel *tunnel) 
	return mtu - PPPOL2TP_HEADER_OVERHEAD;

}



/* connect() handler. Attach a PPPoX socket to a tunnel UDP socket

 */

static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,

			    int sockaddr_len, int flags)

static struct l2tp_tunnel *pppol2tp_tunnel_get(struct net *net,

					       const struct l2tp_connect_info *info,

					       bool *new_tunnel)

{

	struct sock *sk = sock->sk;

	struct pppox_sock *po = pppox_sk(sk);

	struct l2tp_session *session = NULL;

	struct l2tp_connect_info info;

	struct l2tp_tunnel *tunnel;

	struct pppol2tp_session *ps;

	struct l2tp_session_cfg cfg = { 0, };

	bool drop_refcnt = false;

	bool drop_tunnel = false;

	bool new_session = false;

	bool new_tunnel = false;

	int error;



	error = pppol2tp_sockaddr_get_info(uservaddr, sockaddr_len, &info);

	if (error < 0)

		return error;



	lock_sock(sk);



	/* Check for already bound sockets */

	error = -EBUSY;

	if (sk->sk_state & PPPOX_CONNECTED)

		goto end;



	/* We don't supporting rebinding anyway */

	error = -EALREADY;

	if (sk->sk_user_data)

		goto end; /* socket is already attached */



	/* Don't bind if tunnel_id is 0 */

	error = -EINVAL;

	if (!info.tunnel_id)

		goto end;

	*new_tunnel = false;



	tunnel = l2tp_tunnel_get(sock_net(sk), info.tunnel_id);

	if (tunnel)

		drop_tunnel = true;

	tunnel = l2tp_tunnel_get(net, info->tunnel_id);



	/* Special case: create tunnel context if session_id and

	 * peer_session_id is 0. Otherwise look up tunnel using supplied

	 * tunnel id.

	 */

	if (!info.session_id && !info.peer_session_id) {

	if (!info->session_id && !info->peer_session_id) {

		if (!tunnel) {

			struct l2tp_tunnel_cfg tcfg = {

				.encap = L2TP_ENCAPTYPE_UDP,
@@ -706,40 +674,82 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr, 
			/* Prevent l2tp_tunnel_register() from trying to set up

			 * a kernel socket.

			 */

			if (info.fd < 0) {

				error = -EBADF;

				goto end;

			}

			if (info->fd < 0)

				return ERR_PTR(-EBADF);



			error = l2tp_tunnel_create(info.fd,

						   info.version,

						   info.tunnel_id,

						   info.peer_tunnel_id, &tcfg,

			error = l2tp_tunnel_create(info->fd,

						   info->version,

						   info->tunnel_id,

						   info->peer_tunnel_id, &tcfg,

						   &tunnel);

			if (error < 0)

				goto end;

				return ERR_PTR(error);



			l2tp_tunnel_inc_refcount(tunnel);

			error = l2tp_tunnel_register(tunnel, sock_net(sk),

						     &tcfg);

			error = l2tp_tunnel_register(tunnel, net, &tcfg);

			if (error < 0) {

				kfree(tunnel);

				goto end;

				return ERR_PTR(error);

			}

			drop_tunnel = true;

			new_tunnel = true;



			*new_tunnel = true;

		}

	} else {

		/* Error if we can't find the tunnel */

		error = -ENOENT;

		if (!tunnel)

			goto end;

			return ERR_PTR(-ENOENT);



		/* Error if socket is not prepped */

		if (!tunnel->sock)

			goto end;

		if (!tunnel->sock) {

			l2tp_tunnel_dec_refcount(tunnel);

			return ERR_PTR(-ENOENT);

		}

	}



	return tunnel;

}



/* connect() handler. Attach a PPPoX socket to a tunnel UDP socket

 */

static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,

			    int sockaddr_len, int flags)

{

	struct sock *sk = sock->sk;

	struct pppox_sock *po = pppox_sk(sk);

	struct l2tp_session *session = NULL;

	struct l2tp_connect_info info;

	struct l2tp_tunnel *tunnel;

	struct pppol2tp_session *ps;

	struct l2tp_session_cfg cfg = { 0, };

	bool drop_refcnt = false;

	bool new_session = false;

	bool new_tunnel = false;

	int error;



	error = pppol2tp_sockaddr_get_info(uservaddr, sockaddr_len, &info);

	if (error < 0)

		return error;



	/* Don't bind if tunnel_id is 0 */

	if (!info.tunnel_id)

		return -EINVAL;



	tunnel = pppol2tp_tunnel_get(sock_net(sk), &info, &new_tunnel);

	if (IS_ERR(tunnel))

		return PTR_ERR(tunnel);



	lock_sock(sk);



	/* Check for already bound sockets */

	error = -EBUSY;

	if (sk->sk_state & PPPOX_CONNECTED)

		goto end;



	/* We don't supporting rebinding anyway */

	error = -EALREADY;

	if (sk->sk_user_data)

		goto end; /* socket is already attached */



	if (tunnel->peer_tunnel_id == 0)

		tunnel->peer_tunnel_id = info.peer_tunnel_id;
@@ -840,7 +850,6 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr, 
	}

	if (drop_refcnt)

		l2tp_session_dec_refcount(session);

	if (drop_tunnel)

	l2tp_tunnel_dec_refcount(tunnel);

	release_sock(sk);