Re: [PATCH v1] usb: typec: altmodes/displayport: do not index invalid pin_assignments

[Heikki Krogerus <heikki.krogerus@linux.intel.com>]

On Wed, Jun 18, 2025 at 10:49:42PM +0000, RD Babiera wrote:
> 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@vger.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>

> ---
>  drivers/usb/typec/altmodes/displayport.c | 2 +-
>  include/linux/usb/typec_dp.h             | 1 +
>  2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
> index b09b58d7311d..773786129dfb 100644
> --- a/drivers/usb/typec/altmodes/displayport.c
> +++ b/drivers/usb/typec/altmodes/displayport.c
> @@ -677,7 +677,7 @@ 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 f2da264d9c14..acb0ad03bdac 100644
> --- a/include/linux/usb/typec_dp.h
> +++ b/include/linux/usb/typec_dp.h
> @@ -57,6 +57,7 @@ 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 */
> 
> base-commit: e04c78d86a9699d136910cfc0bdcf01087e3267e
> -- 
> 2.50.0.rc2.701.gf1e915cc24-goog

-- 
heikki