usb: typec: tcpm: Fix NULL pointer dereference in tcpm_pd_svdm()

It is possible that typec_register_partner() returns ERR_PTR on failure. When port->partner is an error, a NULL pointer dereference may occur as shown below.

[91222.095236][  T319] typec port0: failed to register partner (-17)
...
[91225.061491][  T319] Unable to handle kernel NULL pointer dereference
at virtual address 000000000000039f
[91225.274642][  T319] pc : tcpm_pd_data_request+0x310/0x13fc
[91225.274646][  T319] lr : tcpm_pd_data_request+0x298/0x13fc
[91225.308067][  T319] Call trace:
[91225.308070][  T319]  tcpm_pd_data_request+0x310/0x13fc
[91225.308073][  T319]  tcpm_pd_rx_handler+0x100/0x9e8
[91225.355900][  T319]  kthread_worker_fn+0x178/0x58c
[91225.355902][  T319]  kthread+0x150/0x200
[91225.355905][  T319]  ret_from_fork+0x10/0x30

Add a check for port->partner to avoid dereferencing a NULL pointer.

Fixes 5e1d4c49fbc8 ("usb: typec: tcpm: Determine common SVDM Version")

Cc [email protected]

Signed-off-by Jimmy Hu <[email protected]>

---
 drivers/usb/typec/tcpm/tcpm.c | 3 +++
 1 file changed, 3 insertions(+)

drivers/usb/typec/tcpm/tcpm.c +3 -0

index 6e843c511b85..792ec4ac7d8d 100644
@@ -1625,6 +1625,9 @@ static int tcpm_pd_svdm(struct tcpm_port *port, struct typec_altmode *adev,
 			if (PD_VDO_VID(p[0]) != USB_SID_PD)
 				break;
 
+			if (IS_ERR_OR_NULL(port->partner))
+				break;
+
 			if (PD_VDO_SVDM_VER(p[0]) < svdm_version) {
 				typec_partner_set_svdm_version(port->partner,
 							       PD_VDO_SVDM_VER(p[0]));