Upon error along the TCP data_ready event path, we have
the following chain of calls:
strp_data_ready()
ovpn_tcp_rcv()
ovpn_peer_del()
ovpn_socket_release()
Since strp_data_ready() may be invoked from softirq context, and
ovpn_socket_release() may sleep, the above sequence may cause a
sleep in atomic context like the following:
BUG: sleeping function called from invalid context at ./ovpn-backports-ovpn-net-next-main-6.15.0-rc5-20250522/drivers/net/ovpn/socket.c:71
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 25, name: ksoftirqd/3
5 locks held by ksoftirqd/3/25:
#0: ffffffe000cd0580 (rcu_read_lock){....}-{1:2}, at: netif_receive_skb+0xb8/0x5b0
OpenVPN/ovpn-backports#1: ffffffe000cd0580 (rcu_read_lock){....}-{1:2}, at: netif_receive_skb+0xb8/0x5b0
OpenVPN/ovpn-backports#2: ffffffe000cd0580 (rcu_read_lock){....}-{1:2}, at: ip_local_deliver_finish+0x66/0x1e0
OpenVPN/ovpn-backports#3: ffffffe003ce9818 (slock-AF_INET/1){+.-.}-{2:2}, at: tcp_v4_rcv+0x156e/0x17a0
OpenVPN/ovpn-backports#4: ffffffe000cd0580 (rcu_read_lock){....}-{1:2}, at: ovpn_tcp_data_ready+0x0/0x1b0 [ovpn]
CPU: 3 PID: 25 Comm: ksoftirqd/3 Not tainted 5.10.104+ #0
Call Trace:
walk_stackframe+0x0/0x1d0
show_stack+0x2e/0x44
dump_stack+0xc2/0x102
___might_sleep+0x29c/0x2b0
__might_sleep+0x62/0xa0
ovpn_socket_release+0x24/0x2d0 [ovpn]
unlock_ovpn+0x6e/0x190 [ovpn]
ovpn_peer_del+0x13c/0x390 [ovpn]
ovpn_tcp_rcv+0x280/0x560 [ovpn]
__strp_recv+0x262/0x940
strp_recv+0x66/0x80
tcp_read_sock+0x122/0x410
strp_data_ready+0x156/0x1f0
ovpn_tcp_data_ready+0x92/0x1b0 [ovpn]
tcp_data_ready+0x6c/0x150
tcp_rcv_established+0xb36/0xc50
tcp_v4_do_rcv+0x25e/0x380
tcp_v4_rcv+0x166a/0x17a0
ip_protocol_deliver_rcu+0x8c/0x250
ip_local_deliver_finish+0xf8/0x1e0
ip_local_deliver+0xc2/0x2d0
ip_rcv+0x1f2/0x330
__netif_receive_skb+0xfc/0x290
netif_receive_skb+0x104/0x5b0
br_pass_frame_up+0x190/0x3f0
br_handle_frame_finish+0x3e2/0x7a0
br_handle_frame+0x750/0xab0
__netif_receive_skb_core.constprop.0+0x4c0/0x17f0
__netif_receive_skb+0xc6/0x290
netif_receive_skb+0x104/0x5b0
xgmac_dma_rx+0x962/0xb40
__napi_poll.constprop.0+0x5a/0x350
net_rx_action+0x1fe/0x4b0
__do_softirq+0x1f8/0x85c
run_ksoftirqd+0x80/0xd0
smpboot_thread_fn+0x1f0/0x3e0
kthread+0x1e6/0x210
ret_from_kernel_thread+0x8/0xc
Fix this issue by postponing the ovpn_peer_del() call to
a scheduled worker, as we already do in ovpn_tcp_send_sock()
for the very same reason.
Fixes: 11851cbd60 ("ovpn: implement TCP transport")
Reported-by: Qingfang Deng <dqfext@gmail.com>
Closes: https://github.com/OpenVPN/ovpn-net-next/issues/13
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
Removing a peer while userspace attempts to close its transport
socket triggers a race condition resulting in the following
crash:
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000077: 0000 [#1] SMP KASAN
KASAN: null-ptr-deref in range [0x00000000000003b8-0x00000000000003bf]
CPU: 12 UID: 0 PID: 162 Comm: kworker/12:1 Tainted: G O 6.15.0-rc2-00635-g521139ac3840 #272 PREEMPT(full)
Tainted: [O]=OOT_MODULE
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-20240910_120124-localhost 04/01/2014
Workqueue: events ovpn_peer_keepalive_work [ovpn]
RIP: 0010:ovpn_socket_release+0x23c/0x500 [ovpn]
Code: ea 03 80 3c 02 00 0f 85 71 02 00 00 48 b8 00 00 00 00 00 fc ff df 4d 8b 64 24 18 49 8d bc 24 be 03 00 00 48 89 fa 48 c1 ea 03 <0f> b6 14 02 48 89 f8 83 e0 07 83 c0 01 38 d0 7c 08 84 d2 0f 85 30
RSP: 0018:ffffc90000c9fb18 EFLAGS: 00010217
RAX: dffffc0000000000 RBX: ffff8881148d7940 RCX: ffffffff817787bb
RDX: 0000000000000077 RSI: 0000000000000008 RDI: 00000000000003be
RBP: ffffc90000c9fb30 R08: 0000000000000000 R09: fffffbfff0d3e840
R10: ffffffff869f4207 R11: 0000000000000000 R12: 0000000000000000
R13: ffff888115eb9300 R14: ffffc90000c9fbc8 R15: 000000000000000c
FS: 0000000000000000(0000) GS:ffff8882b0151000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f37266b6114 CR3: 00000000054a8000 CR4: 0000000000750ef0
PKRU: 55555554
Call Trace:
<TASK>
unlock_ovpn+0x8b/0xe0 [ovpn]
ovpn_peer_keepalive_work+0xe3/0x540 [ovpn]
? ovpn_peers_free+0x780/0x780 [ovpn]
? lock_acquire+0x56/0x70
? process_one_work+0x888/0x1740
process_one_work+0x933/0x1740
? pwq_dec_nr_in_flight+0x10b0/0x10b0
? move_linked_works+0x12d/0x2c0
? assign_work+0x163/0x270
worker_thread+0x4d6/0xd90
? preempt_count_sub+0x4c/0x70
? process_one_work+0x1740/0x1740
kthread+0x36c/0x710
? trace_preempt_on+0x8c/0x1e0
? kthread_is_per_cpu+0xc0/0xc0
? preempt_count_sub+0x4c/0x70
? _raw_spin_unlock_irq+0x36/0x60
? calculate_sigpending+0x7b/0xa0
? kthread_is_per_cpu+0xc0/0xc0
ret_from_fork+0x3a/0x80
? kthread_is_per_cpu+0xc0/0xc0
ret_from_fork_asm+0x11/0x20
</TASK>
Modules linked in: ovpn(O)
This happens because the peer deletion operation reaches
ovpn_socket_release() while ovpn_sock->sock (struct socket *)
and its sk member (struct sock *) are still both valid.
Here synchronize_rcu() is invoked, after which ovpn_sock->sock->sk
becomes NULL, due to the concurrent socket closing triggered
from userspace.
After having invoked synchronize_rcu(), ovpn_socket_release() will
attempt dereferencing ovpn_sock->sock->sk, triggering the crash
reported above.
The reason for accessing sk is that we need to retrieve its
protocol and continue the cleanup routine accordingly.
This crash can be easily produced by running openvpn userspace in
client mode with `--keepalive 10 20`, while entirely omitting this
option on the server side.
After 20 seconds ovpn will assume the peer (server) to be dead,
will start removing it and will notify userspace. The latter will
receive the notification and close the transport socket, thus
triggering the crash.
To fix the race condition for good, we need to refactor struct ovpn_socket.
Since ovpn is always only interested in the sock->sk member (struct sock *)
we can directly hold a reference to it, raher than accessing it via
its struct socket container.
This means changing "struct socket *ovpn_socket->sock" to
"struct sock *ovpn_socket->sk".
While acquiring a reference to sk, we can increase its refcounter
without affecting the socket close()/destroy() notification
(which we rely on when userspace closes a socket we are using).
By increasing sk's refcounter we know we can dereference it
in ovpn_socket_release() without incurring in any race condition
anymore.
ovpn_socket_release() will ultimately decrease the reference
counter.
Cc: Oleksandr Natalenko <oleksandr@natalenko.name>
Fixes: 11851cbd60 ("ovpn: implement TCP transport")
Reported-by: Qingfang Deng <dqfext@gmail.com>
Closes: https://github.com/OpenVPN/ovpn-net-next/issues/1
Tested-by: Gert Doering <gert@greenie.muc.de>
Link: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg31575.html
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
Userspace may want to pass the MSG_NOSIGNAL flag to
tcp_sendmsg() in order to avoid generating a SIGPIPE.
To pass this flag down the TCP stack a new skb sending API
accepting a flags argument is introduced.
Cc: Eric Dumazet <edumazet@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
Link: https://patch.msgid.link/20250415-b4-ovpn-v26-13-577f6097b964@openvpn.net
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
With this change ovpn is allowed to communicate to peers also via TCP.
Parsing of incoming messages is implemented through the strparser API.
Note that ovpn redefines sk_prot and sk_socket->ops for the TCP socket
used to communicate with the peer.
For this reason it needs to access inet6_stream_ops, which is declared
as extern in the IPv6 module, but it is not fully exported.
Therefore this patch is also adding EXPORT_SYMBOL_GPL(inet6_stream_ops)
to net/ipv6/af_inet6.c.
Cc: David Ahern <dsahern@kernel.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Simon Horman <horms@kernel.org>
Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
Link: https://patch.msgid.link/20250415-b4-ovpn-v26-11-577f6097b964@openvpn.net
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
