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l2tp: Avoid possible recursive deadlock in l2tp_tunnel_register()

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[ Upstream commit 9ca5e7ecab ]

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: 0b2c59720e ("l2tp: close all race conditions in l2tp_tunnel_register()")
Cc: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
Reviewed-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Shigeru Yoshida 2023-02-17 01:37:10 +09:00 committed by Greg Kroah-Hartman
parent f7854541b0
commit f6df58aa15
1 changed files with 68 additions and 59 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

127
net/l2tp/l2tp_ppp.c
View File

@ -651,6 +651,65 @@ static int pppol2tp_tunnel_mtu(const struct l2tp_tunnel *tunnel)
return mtu - PPPOL2TP_HEADER_OVERHEAD;
}
static struct l2tp_tunnel *pppol2tp_tunnel_get(struct net *net,
const struct l2tp_connect_info *info,
bool *new_tunnel)
{
struct l2tp_tunnel *tunnel;
int error;
*new_tunnel = false;
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 (!tunnel) {
struct l2tp_tunnel_cfg tcfg = {
.encap = L2TP_ENCAPTYPE_UDP,
};
/* Prevent l2tp_tunnel_register() from trying to set up
* a kernel socket.
*/
if (info->fd < 0)
return ERR_PTR(-EBADF);
error = l2tp_tunnel_create(info->fd,
info->version,
info->tunnel_id,
info->peer_tunnel_id, &tcfg,
&tunnel);
if (error < 0)
return ERR_PTR(error);
l2tp_tunnel_inc_refcount(tunnel);
error = l2tp_tunnel_register(tunnel, net, &tcfg);
if (error < 0) {
kfree(tunnel);
return ERR_PTR(error);
}
*new_tunnel = true;
}
} else {
/* Error if we can't find the tunnel */
if (!tunnel)
return ERR_PTR(-ENOENT);
/* Error if socket is not prepped */
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,
@ -664,7 +723,6 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
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;
@ -673,6 +731,14 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
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 */
@ -685,62 +751,6 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
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;
tunnel = l2tp_tunnel_get(sock_net(sk), info.tunnel_id);
if (tunnel)
drop_tunnel = true;
/* 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 (!tunnel) {
struct l2tp_tunnel_cfg tcfg = {
.encap = L2TP_ENCAPTYPE_UDP,
};
/* Prevent l2tp_tunnel_register() from trying to set up
* a kernel socket.
*/
if (info.fd < 0) {
error = -EBADF;
goto end;
}
error = l2tp_tunnel_create(info.fd,
info.version,
info.tunnel_id,
info.peer_tunnel_id, &tcfg,
&tunnel);
if (error < 0)
goto end;
l2tp_tunnel_inc_refcount(tunnel);
error = l2tp_tunnel_register(tunnel, sock_net(sk),
&tcfg);
if (error < 0) {
kfree(tunnel);
goto end;
}
drop_tunnel = true;
new_tunnel = true;
}
} else {
/* Error if we can't find the tunnel */
error = -ENOENT;
if (!tunnel)
goto end;
/* Error if socket is not prepped */
if (!tunnel->sock)
goto end;
}
if (tunnel->peer_tunnel_id == 0)
tunnel->peer_tunnel_id = info.peer_tunnel_id;
@ -841,8 +851,7 @@ end:
}
if (drop_refcnt)
l2tp_session_dec_refcount(session);
if (drop_tunnel)
l2tp_tunnel_dec_refcount(tunnel);
l2tp_tunnel_dec_refcount(tunnel);
release_sock(sk);
return error;