usb: typec: altmodes/displayport: do not index invalid pin_assignments

commit af4db5a35a4ef7a68046883bfd12468007db38f1 upstream.

A poorly implemented DisplayPort Alt Mode port partner can indicate
that its pin assignment capabilities are greater than the maximum
value, DP_PIN_ASSIGN_F. In this case, calls to pin_assignment_show
will cause a BRK exception due to an out of bounds array access.

Prevent for loop in pin_assignment_show from accessing
invalid values in pin_assignments by adding DP_PIN_ASSIGN_MAX
value in typec_dp.h and using i < DP_PIN_ASSIGN_MAX as a loop
condition.

Fixes: 0e3bb7d6894d ("usb: typec: Add driver for DisplayPort alternate mode")
Cc: stable <stable@kernel.org>
Signed-off-by: RD Babiera <rdbabiera@google.com>
Reviewed-by: Badhri Jagan Sridharan <badhri@google.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20250618224943.3263103-2-rdbabiera@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
index 5f6fc5b79212ef9d322c56605ae18057ab4e523c..2f8d3ed01d5b6e16a23bc447257bdff181b94a64 100644 (file)
--- a/drivers/usb/typec/altmodes/displayport.c
+++ b/drivers/usb/typec/altmodes/displayport.c
@@ -528,7 +528,7 @@ static ssize_t pin_assignment_show(struct device *dev,
 
        assignments = get_current_pin_assignments(dp);
 
-       for (i = 0; assignments; assignments >>= 1, i++) {
+       for (i = 0; assignments && i < DP_PIN_ASSIGN_MAX; assignments >>= 1, i++) {
                if (assignments & 1) {
                        if (i == cur)
                                len += sprintf(buf + len, "[%s] ",

diff --git a/include/linux/usb/typec_dp.h b/include/linux/usb/typec_dp.h
index 8d09c2f0a9b80717cdda7eba91cf63959d3be158..c3f08af20295ca036b5fb0df2eef560d04fd4da1 100644 (file)
--- a/include/linux/usb/typec_dp.h
+++ b/include/linux/usb/typec_dp.h
@@ -56,6 +56,7 @@ enum {
        DP_PIN_ASSIGN_D,
        DP_PIN_ASSIGN_E,
        DP_PIN_ASSIGN_F, /* Not supported after v1.0b */
+       DP_PIN_ASSIGN_MAX,
 };
 
 /* DisplayPort alt mode specific commands */