drm/virtio: fix bounds check in virtio_gpu_cmd_get_capset()

This doesn't affect runtime because in the current code "idx" is always
valid.

First, we read from "vgdev->capsets[idx].max_size" before checking
whether "idx" is within bounds.  And secondly the bounds check is off by
one so we could end up reading one element beyond the end of the
vgdev->capsets[] array.

Fixes: 62fb7a5e1096 ("virtio-gpu: add 3d/virgl support")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20180704094250.m7sgvvzg3dhcvv3h@kili.mountain
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
index 020070d483d350a58695c7fa9f21f7c2be4db463..4735bd1c7321cbfd70e8dc402c31074e1ee9684a 100644 (file)
--- a/drivers/gpu/drm/virtio/virtgpu_vq.c
+++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
@@ -648,11 +648,11 @@ int virtio_gpu_cmd_get_capset(struct virtio_gpu_device *vgdev,
 {
        struct virtio_gpu_get_capset *cmd_p;
        struct virtio_gpu_vbuffer *vbuf;
-       int max_size = vgdev->capsets[idx].max_size;
+       int max_size;
        struct virtio_gpu_drv_cap_cache *cache_ent;
        void *resp_buf;
 
-       if (idx > vgdev->num_capsets)
+       if (idx >= vgdev->num_capsets)
                return -EINVAL;
 
        if (version > vgdev->capsets[idx].max_version)
@@ -662,6 +662,7 @@ int virtio_gpu_cmd_get_capset(struct virtio_gpu_device *vgdev,
        if (!cache_ent)
                return -ENOMEM;
 
+       max_size = vgdev->capsets[idx].max_size;
        cache_ent->caps_cache = kmalloc(max_size, GFP_KERNEL);
        if (!cache_ent->caps_cache) {
                kfree(cache_ent);