[PATCH 5.4 153/168] usb: typec: altmode: Fix typec_altmode_get_partner sometimes returning an invalid pointer

[Greg Kroah-Hartman]

From: Naoki Kiryu <naonaokiryu2@xxxxxxxxx>

commit 0df9433fcae02215c8fd79690c134d535c7bb905 upstream.

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: 5f54a85db5df ("usb: typec: Make sure an alt mode exist before getting its partner")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Naoki Kiryu <naonaokiryu2@xxxxxxxxx>
Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20200422144345.43262-1-hdegoede@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/usb/typec/bus.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/usb/typec/bus.c
+++ b/drivers/usb/typec/bus.c
@@ -192,7 +192,10 @@ 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);