Re: [PATCH] drm/panthor: validate userspace queue count against initialized firmware slot count

[Boris Brezillon <boris.brezillon@collabora.com>]

On Tue,  4 Aug 2026 18:00:47 +0200
Osama Abdelkader <osama.abdelkader@gmail.com> wrote:

> In panthor_drv.c:panthor_ioctl_group_create(),
> the queue count is validated against the hardcoded maximum:
> 
> 	if (!args->queues.count || args->queues.count > MAX_CS_PER_CSG)
> 		return -EINVAL;
> 
> However, if the firmware reports fewer slots than MAX_CS_PER_CSG,
> panthor_fw_init_ifaces() will only initialize that smaller number of
> stream interfaces.
> 
> If unprivileged userspace requests more queues than the firmware reported
> (but no more than MAX_CS_PER_CSG), cs_slot_prog_locked() fetches an
> uninitialized stream interface and may crash when dereferencing
> cs_iface->input->ringbuf_base.
> 
> Fixes: de8548813824 ("drm/panthor: Add the scheduler logical block")
> Cc: stable@vger.kernel.org
> Reported-by: sashiko-bot@kernel.org
> Closes: https://sashiko.dev/#/patchset/20260803141149.68182-1-osama.abdelkader@gmail.com?part=1
> Signed-off-by: Osama Abdelkader <osama.abdelkader@gmail.com>

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

> ---
>  drivers/gpu/drm/panthor/panthor_sched.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
> index 5832dccfc093..64749750e6ee 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.c
> +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> @@ -3673,6 +3673,9 @@ int panthor_group_create(struct panthor_file *pfile,
>  	    hweight64(group_args->tiler_core_mask) < group_args->max_tiler_cores)
>  		return -EINVAL;
>  
> +	if (group_args->queues.count > sched->cs_slot_count)
> +		return -EINVAL;
> +
>  	group = kzalloc_obj(*group);
>  	if (!group)
>  		return -ENOMEM;