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>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
index 020070d483d3..4735bd1c7321 100644
--- 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);