usb: typec: altmode: Fix typec_altmode_get_partner sometimes returning an invalid pointer

Before this commit, typec_altmode_get_partner would return a
const struct typec_altmode * pointing to address 0x08 when
to_altmode(adev)->partner was NULL.

Add a check for to_altmode(adev)->partner being NULL to fix this.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=206365
BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1785972
Fixes: 5f54a85 ("usb: typec: Make sure an alt mode exist before getting its partner")
Cc: [email protected]
Signed-off-by: Naoki Kiryu <[email protected]>
Signed-off-by: Hans de Goede <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: grainrigi

drivers/usb/typec/bus.c

@@ -198,7 +198,10 @@ EXPORT_SYMBOL_GPL(typec_altmode_vdm);
 const struct typec_altmode *
 typec_altmode_get_partner(struct typec_altmode *adev)
 {
-	return adev ? &to_altmode(adev)->partner->adev : NULL;
+	if (!adev || !to_altmode(adev)->partner)
+		return NULL;
+
+	return &to_altmode(adev)->partner->adev;
 }
 EXPORT_SYMBOL_GPL(typec_altmode_get_partner);