[PATCH v1] usb: typec: ucsi: displayport: Fix OOB altmode array index

[PATCH v1] usb: typec: ucsi: displayport: Fix OOB altmode array index

[Jameson Thies]

The UCSI displayport driver indexes the connector's port altmode array
with the GET_CURRENT_CAM response after checking it is not 0xff. The
port altmode array is UCSI_MAX_ALTMODES elements long. If the PPM
returns an invalid GET_CURRENT_CAM response above UCSI_MAX_ALTMODES and
not equal to 0xff, the kernel may crash with an array index OOB error.

Update the UCSI displayport driver to verify the current cam is less
than UCSI_MAX_ALTMODES before accessing the port altmode array.

Fixes: af8622f6a585 ("usb: typec: ucsi: Support for DisplayPort alt mode")
Cc: stable@vger.kernel.org
Signed-off-by: Jameson Thies <jthies@google.com>
---
 drivers/usb/typec/ucsi/displayport.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/typec/ucsi/displayport.c b/drivers/usb/typec/ucsi/displayport.c
index 7067f2561b84..8d2032d0762c 100644
--- a/drivers/usb/typec/ucsi/displayport.c
+++ b/drivers/usb/typec/ucsi/displayport.c
@@ -74,7 +74,7 @@ static int ucsi_displayport_enter(struct typec_altmode *alt, u32 *vdo)
 		cur = 0xff;
 	}
 
-	if (cur != 0xff) {
+	if (cur < UCSI_MAX_ALTMODES) {
 		ret = dp->con->port_altmode[cur] == alt ? 0 : -EBUSY;
 		goto err_unlock;
 	}

base-commit: e1e6e541c5c9cf548e9fdc35fc26808c82074440
-- 
2.55.0.860.g4b6b3295ed-goog

Re: [PATCH v1] usb: typec: ucsi: displayport: Fix OOB altmode array index

[Benson Leung]

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On Tue, Aug 25, 2026 at 11:45:45PM +0000, Jameson Thies wrote:
> The UCSI displayport driver indexes the connector's port altmode array
> with the GET_CURRENT_CAM response after checking it is not 0xff. The
> port altmode array is UCSI_MAX_ALTMODES elements long. If the PPM
> returns an invalid GET_CURRENT_CAM response above UCSI_MAX_ALTMODES and
> not equal to 0xff, the kernel may crash with an array index OOB error.
> 
> Update the UCSI displayport driver to verify the current cam is less
> than UCSI_MAX_ALTMODES before accessing the port altmode array.
> 
> Fixes: af8622f6a585 ("usb: typec: ucsi: Support for DisplayPort alt mode")
> Cc: stable@vger.kernel.org
> Signed-off-by: Jameson Thies <jthies@google.com>

Reviewed-by: Benson Leung <bleung@chromium.org>


> ---
>  drivers/usb/typec/ucsi/displayport.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/typec/ucsi/displayport.c b/drivers/usb/typec/ucsi/displayport.c
> index 7067f2561b84..8d2032d0762c 100644
> --- a/drivers/usb/typec/ucsi/displayport.c
> +++ b/drivers/usb/typec/ucsi/displayport.c
> @@ -74,7 +74,7 @@ static int ucsi_displayport_enter(struct typec_altmode *alt, u32 *vdo)
>  		cur = 0xff;
>  	}
>  
> -	if (cur != 0xff) {
> +	if (cur < UCSI_MAX_ALTMODES) {
>  		ret = dp->con->port_altmode[cur] == alt ? 0 : -EBUSY;
>  		goto err_unlock;
>  	}
> 
> base-commit: e1e6e541c5c9cf548e9fdc35fc26808c82074440
> -- 
> 2.55.0.860.g4b6b3295ed-goog
> 

[-- Attachment #2: signature.asc --]
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Re: [PATCH v1] usb: typec: ucsi: displayport: Fix OOB altmode array index

[Heikki Krogerus]

On Tue, Aug 25, 2026 at 11:45:45PM +0000, Jameson Thies wrote:
> The UCSI displayport driver indexes the connector's port altmode array
> with the GET_CURRENT_CAM response after checking it is not 0xff. The
> port altmode array is UCSI_MAX_ALTMODES elements long. If the PPM
> returns an invalid GET_CURRENT_CAM response above UCSI_MAX_ALTMODES and
> not equal to 0xff, the kernel may crash with an array index OOB error.
> 
> Update the UCSI displayport driver to verify the current cam is less
> than UCSI_MAX_ALTMODES before accessing the port altmode array.
> 
> Fixes: af8622f6a585 ("usb: typec: ucsi: Support for DisplayPort alt mode")
> Cc: stable@vger.kernel.org
> Signed-off-by: Jameson Thies <jthies@google.com>
> ---
>  drivers/usb/typec/ucsi/displayport.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/typec/ucsi/displayport.c b/drivers/usb/typec/ucsi/displayport.c
> index 7067f2561b84..8d2032d0762c 100644
> --- a/drivers/usb/typec/ucsi/displayport.c
> +++ b/drivers/usb/typec/ucsi/displayport.c
> @@ -74,7 +74,7 @@ static int ucsi_displayport_enter(struct typec_altmode *alt, u32 *vdo)
>  		cur = 0xff;

Can you remove the above line while at it?

>  	}
>  
> -	if (cur != 0xff) {
> +	if (cur < UCSI_MAX_ALTMODES) {

Shouldn't that be the other way around?

>  		ret = dp->con->port_altmode[cur] == alt ? 0 : -EBUSY;
>  		goto err_unlock;
>  	}

Thanks,

-- 
heikki

Re: [PATCH v1] usb: typec: ucsi: displayport: Fix OOB altmode array index

[Andrei Kuchynski]

On Mon, Aug 31, 2026 at 12:37 PM Heikki Krogerus
<heikki.krogerus@linux.intel.com> wrote:
>
> On Tue, Aug 25, 2026 at 11:45:45PM +0000, Jameson Thies wrote:
> > The UCSI displayport driver indexes the connector's port altmode array
> > with the GET_CURRENT_CAM response after checking it is not 0xff. The
> > port altmode array is UCSI_MAX_ALTMODES elements long. If the PPM
> > returns an invalid GET_CURRENT_CAM response above UCSI_MAX_ALTMODES and
> > not equal to 0xff, the kernel may crash with an array index OOB error.
> >
> > Update the UCSI displayport driver to verify the current cam is less
> > than UCSI_MAX_ALTMODES before accessing the port altmode array.
> >
> > Fixes: af8622f6a585 ("usb: typec: ucsi: Support for DisplayPort alt mode")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Jameson Thies <jthies@google.com>
> > ---
> >  drivers/usb/typec/ucsi/displayport.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/usb/typec/ucsi/displayport.c b/drivers/usb/typec/ucsi/displayport.c
> > index 7067f2561b84..8d2032d0762c 100644
> > --- a/drivers/usb/typec/ucsi/displayport.c
> > +++ b/drivers/usb/typec/ucsi/displayport.c
> > @@ -74,7 +74,7 @@ static int ucsi_displayport_enter(struct typec_altmode *alt, u32 *vdo)
> >               cur = 0xff;
>
> Can you remove the above line while at it?
>
> >       }
> >
> > -     if (cur != 0xff) {
> > +     if (cur < UCSI_MAX_ALTMODES) {
>
> Shouldn't that be the other way around?
>

Looks fine, but shouldn't we return an error if an invalid value is
received, similar to the Thunderbolt implementation?

        if (cur != 0xff) {
                if (cur >= UCSI_MAX_ALTMODES ||
dp->con->port_altmode[cur] != alt)
                        ret = -EBUSY;
                else
                        ret = 0;
                goto err_unlock;

Thanks,
Andrei

Re: [PATCH v1] usb: typec: ucsi: displayport: Fix OOB altmode array index

[Jameson Thies]

Hi Heikki and Andrei,
thanks for taking a look. I'll follow up with a v2 of this patch to
address your comments. Answers below with some additional comments.

> > Can you remove the above line while at it?

Will remove in v2.

> > Shouldn't that be the other way around?

I'm not sure I understand. Because UCSI_MAX_ALTMODES is set to 30 in
ucsi.h, verifying 'cur' is less than UCSI_MAX_ALTMODES will still
evaluate to false if 'cur' is 0xff. This update maintains the existing
functionality and prevents the driver from using an out of bounds
index.

> Looks fine, but shouldn't we return an error if an invalid value is
> received, similar to the Thunderbolt implementation?

Sounds good to me, but I think we should split up the
UCSI_MAX_ALTMODES check and the port_altmode check. Returning EBUSY
doesn't seem like an appropriate error code if the PPM returns an out
of range option. I think we should return EINVAL here.