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Date: Mon, 13 Feb 2023 01:26:23 +0900
From: Shigeru Yoshida <syoshida@...hat.com>
To: jchapman@...alix.com, davem@...emloft.net, edumazet@...gle.com,
kuba@...nel.org, pabeni@...hat.com
Cc: gnault@...hat.com, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, Shigeru Yoshida <syoshida@...hat.com>
Subject: [PATCH v2] 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: 0b2c59720e65 ("l2tp: close all race conditions in l2tp_tunnel_register()")
Signed-off-by: Shigeru Yoshida <syoshida@...hat.com>
---
v2: Get/create the tunnel before locking the pppol2tp socket suggested
by Guillaume Nault.
v1: https://lore.kernel.org/all/20230130154438.1373750-1-syoshida@redhat.com/
net/l2tp/l2tp_ppp.c | 118 ++++++++++++++++++++++++--------------------
1 file changed, 64 insertions(+), 54 deletions(-)
diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index db2e584c625e..68d02e217ca3 100644
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -650,6 +650,65 @@ 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,
+ 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,
@@ -663,7 +722,6 @@ 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;
@@ -672,6 +730,10 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
if (error < 0)
return error;
+ 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 */
@@ -689,57 +751,6 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
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;
@@ -840,8 +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;
--
2.39.0
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