[Intel-xe] [PATCH 2/2] drm/xe: properly check bounds for xe_wait_user_fence_ioctl()

[Paulo Zanoni]

If !no_engines, then we use copy_from_user to copy to the 'eci' array,
which has XE_HW_ENGINE_MAX_INSTANCE members. The amount of members
copied is given by the user in args->num_engines, so add code to check
that args->num_engines does not exceed XE_HW_ENGINE_MAX_INSTANCE. It's
an unsigned value so there's no need to check for negative values.

Fixes error messages such as:

    Buffer overflow detected (54 < 18446744073709551520)!

Very simple reproducer:

    https://people.freedesktop.org/~pzanoni/wait-user-fence-bug/

Reviewed-by: José Roberto de Souza <jose.souza at intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
---
 drivers/gpu/drm/xe/xe_wait_user_fence.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_wait_user_fence.c b/drivers/gpu/drm/xe/xe_wait_user_fence.c
index 3122374341d6..098e2a4cff3f 100644
--- a/drivers/gpu/drm/xe/xe_wait_user_fence.c
+++ b/drivers/gpu/drm/xe/xe_wait_user_fence.c
@@ -121,6 +121,9 @@ int xe_wait_user_fence_ioctl(struct drm_device *dev, void *data,
 			 addr & 0x7))
 		return -EINVAL;
 
+	if (XE_IOCTL_ERR(xe, args->num_engines > XE_HW_ENGINE_MAX_INSTANCE))
+		return -EINVAL;
+
 	if (!no_engines) {
 		err = copy_from_user(eci, user_eci,
 				     sizeof(struct drm_xe_engine_class_instance) *
-- 
2.39.2