[PATCH] usb: typec: ucsi: Fix NULL pointer dereference in power level debugfs

[Bertrand Jacquin <bertrand@jacquin.bzh>]

ucsi_register() creates the debugfs entries right away, but
ucsi->connector is only set by ucsi_init(), which runs later from
ucsi->work and only publishes the connectors once the PPM has been
reset and all ports are registered. Until then, or for good if init
fails, ucsi->connector is NULL, yet the peak_current, avg_current and
vbus_voltage show callbacks dereference it unconditionally.

On an Intel NUC13ANKi5 whose PPM never answers when CONFIG_ACPI_EC=n,
reading those files after the failed init oopses:

  ucsi_acpi USBC000:00: error -ETIMEDOUT: PPM init failed
  BUG: kernel NULL pointer dereference, address: 000000000000045c
  #PF: supervisor read access in kernel mode
  RIP: 0010:ucsi_debugfs_register+0x291/0x420 [typec_ucsi]
  Call Trace:
   <TASK>
   seq_read_iter+0x1e4/0x4c0
   seq_read+0x12b/0x160
   full_proxy_read+0x9a/0x1f0
   vfs_read+0xba/0x320
   ksys_read+0x74/0x110
   do_syscall_64+0x79/0x240
   entry_SYSCALL_64_after_hwframe+0x71/0x79

Return -ENODEV from those callbacks while no connector is available.

Fixes: c851b71fd6cd ("usb: typec: ucsi: Add support for READ_POWER_LEVEL command")
Cc: stable@vger.kernel.org
Signed-off-by: Bertrand Jacquin <bertrand@jacquin.bzh>
---
 drivers/usb/typec/ucsi/debugfs.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/usb/typec/ucsi/debugfs.c b/drivers/usb/typec/ucsi/debugfs.c
index 77a0dd75edd3..911a151ac16a 100644
--- a/drivers/usb/typec/ucsi/debugfs.c
+++ b/drivers/usb/typec/ucsi/debugfs.c
@@ -92,6 +92,9 @@ static int ucsi_peak_curr_show(struct seq_file *m, void *v)
 {
 	struct ucsi *ucsi = m->private;
 
+	if (!ucsi->connector)
+		return -ENODEV;
+
 	seq_printf(m, "%u mA\n", ucsi->connector->peak_current);
 	return 0;
 }
@@ -101,6 +104,9 @@ static int ucsi_avg_curr_show(struct seq_file *m, void *v)
 {
 	struct ucsi *ucsi = m->private;
 
+	if (!ucsi->connector)
+		return -ENODEV;
+
 	seq_printf(m, "%u mA\n", ucsi->connector->avg_current);
 	return 0;
 }
@@ -110,6 +116,9 @@ static int ucsi_vbus_volt_show(struct seq_file *m, void *v)
 {
 	struct ucsi *ucsi = m->private;
 
+	if (!ucsi->connector)
+		return -ENODEV;
+
 	seq_printf(m, "%u mV\n", ucsi->connector->vbus_voltage);
 	return 0;
 }