Re: [PATCH v1] usb: typec: tcpm: Defensively bound altmode array accesses

[Heikki Krogerus]

On Mon, Jun 29, 2026 at 10:57:29PM +0000, Badhri Jagan Sridharan wrote:
> While svdm_consume_modes() already prevents mode_data.altmodes from
> exceeding ALTMODE_DISCOVERY_MAX during SVDM discovery, defensively
> bounding array iteration indices against ALTMODE_DISCOVERY_MAX in altmode
> registration and unregistration helpers guarantees protection against
> out-of-bounds accesses in the event of memory corruption.
> 
> Ensure that tcpm_register_plug_altmodes() is also bounded alongside
> tcpm_register_partner_altmodes() and tcpm_unregister_altmodes.
> 
> Assisted-by: Antigravity:gemini-3.5-flash
> Signed-off-by: Badhri Jagan Sridharan <badhri@xxxxxxxxxx>
> Reviewed-by: RD Babiera <rdbabiera@xxxxxxxxxx>

Acked-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>

> ---
>  drivers/usb/typec/tcpm/tcpm.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index 7ef746a90a17..c9ac9381b17c 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -2029,7 +2029,7 @@ static void tcpm_register_partner_altmodes(struct tcpm_port *port)
>  	if (!port->partner)
>  		return;
>  
> -	for (i = 0; i < modep->altmodes; i++) {
> +	for (i = 0; i < modep->altmodes && i < ALTMODE_DISCOVERY_MAX; i++) {
>  		altmode = typec_partner_register_altmode(port->partner,
>  						&modep->altmode_desc[i]);
>  		if (IS_ERR(altmode)) {
> @@ -2047,9 +2047,10 @@ static void tcpm_register_plug_altmodes(struct tcpm_port *port)
>  	struct typec_altmode *altmode;
>  	int i;
>  
> -	typec_plug_set_num_altmodes(port->plug_prime, modep->altmodes);
> +	typec_plug_set_num_altmodes(port->plug_prime,
> +				    min(modep->altmodes, ALTMODE_DISCOVERY_MAX));
>  
> -	for (i = 0; i < modep->altmodes; i++) {
> +	for (i = 0; i < modep->altmodes && i < ALTMODE_DISCOVERY_MAX; i++) {
>  		altmode = typec_plug_register_altmode(port->plug_prime,
>  						&modep->altmode_desc[i]);
>  		if (IS_ERR(altmode)) {
> @@ -4891,11 +4892,11 @@ static void tcpm_unregister_altmodes(struct tcpm_port *port)
>  	struct pd_mode_data *modep_prime = &port->mode_data_prime;
>  	int i;
>  
> -	for (i = 0; i < modep->altmodes; i++) {
> +	for (i = 0; i < modep->altmodes && i < ALTMODE_DISCOVERY_MAX; i++) {
>  		typec_unregister_altmode(port->partner_altmode[i]);
>  		port->partner_altmode[i] = NULL;
>  	}
> -	for (i = 0; i < modep_prime->altmodes; i++) {
> +	for (i = 0; i < modep_prime->altmodes && i < ALTMODE_DISCOVERY_MAX; i++) {
>  		typec_unregister_altmode(port->plug_prime_altmode[i]);
>  		port->plug_prime_altmode[i] = NULL;
>  	}
> 
> base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
> -- 
> 2.55.0.rc0.799.gd6f94ed593-goog

-- 
heikki