This is a note to let you know that I've just added the patch titled
l2tp: Avoid possible recursive deadlock in l2tp_tunnel_register()
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
l2tp-avoid-possible-recursive-deadlock-in-l2tp_tunne.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 6eb8547aa792e065491a2de21ead08e7313572c3
Author: Shigeru Yoshida <syoshida@xxxxxxxxxx>
Date: Fri Feb 17 01:37:10 2023 +0900
l2tp: Avoid possible recursive deadlock in l2tp_tunnel_register()
[ Upstream commit 9ca5e7ecab064f1f47da07f7c1ddf40e4bc0e5ac ]
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: 0b2c59720e65 ("l2tp: close all race conditions in l2tp_tunnel_register()")
Cc: Cong Wang <cong.wang@xxxxxxxxxxxxx>
Signed-off-by: Shigeru Yoshida <syoshida@xxxxxxxxxx>
Reviewed-by: Guillaume Nault <gnault@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index aea85f91f0599..5ecc0f2009444 100644
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -651,54 +651,22 @@ 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;
+ *new_tunnel = false;
- 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;
-
- 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,
@@ -707,40 +675,82 @@ 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;
@@ -841,8 +851,7 @@ 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);
+ l2tp_tunnel_dec_refcount(tunnel);
release_sock(sk);
return error;
