[PATCH net 3/5] ovpn: avoid sleep in atomic context in TCP RX error path

[Antonio Quartulli <antonio@openvpn.net>]

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: 11851cbd60ea ("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>
---
 drivers/net/ovpn/tcp.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ovpn/tcp.c b/drivers/net/ovpn/tcp.c
index 7e79aad0b043..289f62c5d2c7 100644
--- a/drivers/net/ovpn/tcp.c
+++ b/drivers/net/ovpn/tcp.c
@@ -124,14 +124,18 @@ static void ovpn_tcp_rcv(struct strparser *strp, struct sk_buff *skb)
 	 * this peer, therefore ovpn_peer_hold() is not expected to fail
 	 */
 	if (WARN_ON(!ovpn_peer_hold(peer)))
-		goto err;
+		goto err_nopeer;
 
 	ovpn_recv(peer, skb);
 	return;
 err:
+	/* take reference for deferred peer deletion. should never fail */
+	if (WARN_ON(!ovpn_peer_hold(peer)))
+		goto err_nopeer;
+	schedule_work(&peer->tcp.defer_del_work);
 	dev_dstats_rx_dropped(peer->ovpn->dev);
+err_nopeer:
 	kfree_skb(skb);
-	ovpn_peer_del(peer, OVPN_DEL_PEER_REASON_TRANSPORT_ERROR);
 }
 
 static int ovpn_tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
-- 
2.49.0