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

[Osama Abdelkader <osama.abdelkader@gmail.com>]

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>
---
 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;
-- 
2.43.0